diff options
| author | Arnold D. Robbins <arnold@skeeve.com> | 2014-08-29 13:19:10 +0300 |
|---|---|---|
| committer | Arnold D. Robbins <arnold@skeeve.com> | 2014-08-29 13:19:10 +0300 |
| commit | ba1e7ab66563efb5b597a418e2e9fb4a01998d03 (patch) | |
| tree | a9cf2a74f9fd34725a507a3b9cef8bd1566a1664 | |
| parent | 5a05ddf24b9f5ebc81a1b295ba7a6fbc7348776b (diff) | |
| parent | 6c541fd0f75cd328dd80afec757ecccc833719af (diff) | |
| download | gawk-ba1e7ab66563efb5b597a418e2e9fb4a01998d03.tar.gz | |
Merge branch 'gawk-4.1-stable'
| -rw-r--r-- | awklib/eg/lib/getopt.awk | 3 | ||||
| -rw-r--r-- | awklib/eg/lib/strtonum.awk | 7 | ||||
| -rw-r--r-- | doc/ChangeLog | 5 | ||||
| -rw-r--r-- | doc/gawk.info | 1507 | ||||
| -rw-r--r-- | doc/gawk.texi | 549 | ||||
| -rw-r--r-- | doc/gawktexi.in | 461 |
6 files changed, 1326 insertions, 1206 deletions
diff --git a/awklib/eg/lib/getopt.awk b/awklib/eg/lib/getopt.awk index db957ceb..6b1f4c50 100644 --- a/awklib/eg/lib/getopt.awk +++ b/awklib/eg/lib/getopt.awk @@ -38,8 +38,7 @@ function getopt(argc, argv, options, thisopt, i) i = index(options, thisopt) if (i == 0) { if (Opterr) - printf("%c -- invalid option\n", - thisopt) > "/dev/stderr" + printf("%c -- invalid option\n", thisopt) > "/dev/stderr" if (_opti >= length(argv[Optind])) { Optind++ _opti = 0 diff --git a/awklib/eg/lib/strtonum.awk b/awklib/eg/lib/strtonum.awk index 9342e789..5e20626b 100644 --- a/awklib/eg/lib/strtonum.awk +++ b/awklib/eg/lib/strtonum.awk @@ -13,8 +13,9 @@ function mystrtonum(str, ret, n, i, k, c) ret = 0 for (i = 1; i <= n; i++) { c = substr(str, i, 1) - if ((k = index("01234567", c)) > 0) - k-- # adjust for 1-basing in awk + # index() returns 0 if c not in string, + # includes c == "0" + k = index("1234567", c) ret = ret * 8 + k } @@ -26,6 +27,8 @@ function mystrtonum(str, ret, n, i, k, c) for (i = 1; i <= n; i++) { c = substr(str, i, 1) c = tolower(c) + # index() returns 0 if c not in string, + # includes c == "0" k = index("123456789abcdef", c) ret = ret * 16 + k diff --git a/doc/ChangeLog b/doc/ChangeLog index b6a13dc7..4eaa8138 100644 --- a/doc/ChangeLog +++ b/doc/ChangeLog @@ -1,3 +1,8 @@ +2014-08-29 Arnold D. Robbins <arnold@skeeve.com> + + * gawktexi.in: Continuing on reviewer comments, and other + bug fixes, miscellanious improvements. + 2014-08-26 Arnold D. Robbins <arnold@skeeve.com> * gawktexi.in: Use a different mechanism to exclude diff --git a/doc/gawk.info b/doc/gawk.info index 514965f4..afa825cc 100644 --- a/doc/gawk.info +++ b/doc/gawk.info @@ -170,10 +170,10 @@ entitled "GNU Free Documentation License". * Escape Sequences:: How to write nonprinting characters. * Regexp Operators:: Regular Expression Operators. * Bracket Expressions:: What can go between `[...]'. -* GNU Regexp Operators:: Operators specific to GNU software. -* Case-sensitivity:: How to do case-insensitive matching. * Leftmost Longest:: How much text matches. * Computed Regexps:: Using Dynamic Regexps. +* GNU Regexp Operators:: Operators specific to GNU software. +* Case-sensitivity:: How to do case-insensitive matching. * Regexp Summary:: Regular expressions summary. * Records:: Controlling how data is split into records. @@ -1455,15 +1455,17 @@ end-of-file character may be different. For example, on OS/2, it is As an example, the following program prints a friendly piece of advice (from Douglas Adams's `The Hitchhiker's Guide to the Galaxy'), to keep you from worrying about the complexities of computer -programming (`BEGIN' is a feature we haven't discussed yet): +programming: - $ awk "BEGIN { print \"Don't Panic!\" }" + $ awk "BEGIN { print "Don\47t Panic!" }" -| Don't Panic! - This program does not read any input. The `\' before each of the -inner double quotes is necessary because of the shell's quoting -rules--in particular because it mixes both single quotes and double -quotes.(1) + `awk' executes statements associated with `BEGIN' before reading any +input. If there are no other statements in your program, as is the +case here, `awk' just stops, instead of trying to read input it doesn't +know how to process. The `\47' is a magic way of getting a single +quote into the program, without having to engage in ugly shell quoting +tricks. NOTE: As a side note, if you use Bash as your shell, you should execute the command `set +H' before running this program @@ -1486,12 +1488,6 @@ works is explained shortly). -| What, me worry? Ctrl-d - ---------- Footnotes ---------- - - (1) Although we generally recommend the use of single quotes around -the program text, double quotes are needed here in order to put the -single quote into the message. - File: gawk.info, Node: Long, Next: Executable Scripts, Prev: Read Terminal, Up: Running gawk @@ -1937,6 +1933,9 @@ different ways to do the same things shown here: awk '{ if (length($0) > max) max = length($0) } END { print max }' data + The code associated with `END' executes after all input has been + read; it's the other side of the coin to `BEGIN'. + * Print the length of the longest line in `data': expand data | awk '{ if (x < length($0)) x = length($0) } @@ -2729,6 +2728,10 @@ arguments, including variable assignments, are included. As each element of `ARGV' is processed, `gawk' sets the variable `ARGIND' to the index in `ARGV' of the current element. + Changing `ARGC' and `ARGV' in your `awk' program lets you control +how `awk' processes the input files; this is described in more detail +in *note ARGC and ARGV::. + The distinction between file name arguments and variable-assignment arguments is made when `awk' is about to open the next input file. At that point in execution, it checks the file name to see whether it is @@ -3218,10 +3221,10 @@ you specify more complicated classes of strings. * Escape Sequences:: How to write nonprinting characters. * Regexp Operators:: Regular Expression Operators. * Bracket Expressions:: What can go between `[...]'. -* GNU Regexp Operators:: Operators specific to GNU software. -* Case-sensitivity:: How to do case-insensitive matching. * Leftmost Longest:: How much text matches. * Computed Regexps:: Using Dynamic Regexps. +* GNU Regexp Operators:: Operators specific to GNU software. +* Case-sensitivity:: How to do case-insensitive matching. * Regexp Summary:: Regular expressions summary. @@ -3363,17 +3366,19 @@ apply to both string constants and regexp constants: `\/' A literal slash (necessary for regexp constants only). This sequence is used when you want to write a regexp constant that - contains a slash. Because the regexp is delimited by slashes, you - need to escape the slash that is part of the pattern, in order to + contains a slash (such as `/.*:\/home\/[[:alnum:]]+:.*/'; the + `[[:alnum:]]' notation is discussed shortly, in *note Bracket + Expressions::). Because the regexp is delimited by slashes, you + need to escape any slash that is part of the pattern, in order to tell `awk' to keep processing the rest of the regexp. `\"' A literal double quote (necessary for string constants only). This sequence is used when you want to write a string constant - that contains a double quote. Because the string is delimited by - double quotes, you need to escape the quote that is part of the - string, in order to tell `awk' to keep processing the rest of the - string. + that contains a double quote (such as `"He said \"hi!\" to her."'). + Because the string is delimited by double quotes, you need to + escape any quote that is part of the string, in order to tell + `awk' to keep processing the rest of the string. In `gawk', a number of additional two-character sequences that begin with a backslash have special meaning in regexps. *Note GNU Regexp @@ -3611,7 +3616,7 @@ list". regexp operator or function. -File: gawk.info, Node: Bracket Expressions, Next: GNU Regexp Operators, Prev: Regexp Operators, Up: Regexp +File: gawk.info, Node: Bracket Expressions, Next: Leftmost Longest, Prev: Regexp Operators, Up: Regexp 3.4 Using Bracket Expressions ============================= @@ -3716,9 +3721,118 @@ Equivalence classes classes. -File: gawk.info, Node: GNU Regexp Operators, Next: Case-sensitivity, Prev: Bracket Expressions, Up: Regexp +File: gawk.info, Node: Leftmost Longest, Next: Computed Regexps, Prev: Bracket Expressions, Up: Regexp + +3.5 How Much Text Matches? +========================== -3.5 `gawk'-Specific Regexp Operators +Consider the following: + + echo aaaabcd | awk '{ sub(/a+/, "<A>"); print }' + + This example uses the `sub()' function (which we haven't discussed +yet; *note String Functions::) to make a change to the input record. +Here, the regexp `/a+/' indicates "one or more `a' characters," and the +replacement text is `<A>'. + + The input contains four `a' characters. `awk' (and POSIX) regular +expressions always match the leftmost, _longest_ sequence of input +characters that can match. Thus, all four `a' characters are replaced +with `<A>' in this example: + + $ echo aaaabcd | awk '{ sub(/a+/, "<A>"); print }' + -| <A>bcd + + For simple match/no-match tests, this is not so important. But when +doing text matching and substitutions with the `match()', `sub()', +`gsub()', and `gensub()' functions, it is very important. *Note String +Functions::, for more information on these functions. Understanding +this principle is also important for regexp-based record and field +splitting (*note Records::, and also *note Field Separators::). + + +File: gawk.info, Node: Computed Regexps, Next: GNU Regexp Operators, Prev: Leftmost Longest, Up: Regexp + +3.6 Using Dynamic Regexps +========================= + +The righthand side of a `~' or `!~' operator need not be a regexp +constant (i.e., a string of characters between slashes). It may be any +expression. The expression is evaluated and converted to a string if +necessary; the contents of the string are then used as the regexp. A +regexp computed in this way is called a "dynamic regexp" or a "computed +regexp": + + BEGIN { digits_regexp = "[[:digit:]]+" } + $0 ~ digits_regexp { print } + +This sets `digits_regexp' to a regexp that describes one or more digits, +and tests whether the input record matches this regexp. + + NOTE: When using the `~' and `!~' operators, there is a difference + between a regexp constant enclosed in slashes and a string + constant enclosed in double quotes. If you are going to use a + string constant, you have to understand that the string is, in + essence, scanned _twice_: the first time when `awk' reads your + program, and the second time when it goes to match the string on + the lefthand side of the operator with the pattern on the right. + This is true of any string-valued expression (such as + `digits_regexp', shown previously), not just string constants. + + What difference does it make if the string is scanned twice? The +answer has to do with escape sequences, and particularly with +backslashes. To get a backslash into a regular expression inside a +string, you have to type two backslashes. + + For example, `/\*/' is a regexp constant for a literal `*'. Only +one backslash is needed. To do the same thing with a string, you have +to type `"\\*"'. The first backslash escapes the second one so that +the string actually contains the two characters `\' and `*'. + + Given that you can use both regexp and string constants to describe +regular expressions, which should you use? The answer is "regexp +constants," for several reasons: + + * String constants are more complicated to write and more difficult + to read. Using regexp constants makes your programs less + error-prone. Not understanding the difference between the two + kinds of constants is a common source of errors. + + * It is more efficient to use regexp constants. `awk' can note that + you have supplied a regexp and store it internally in a form that + makes pattern matching more efficient. When using a string + constant, `awk' must first convert the string into this internal + form and then perform the pattern matching. + + * Using regexp constants is better form; it shows clearly that you + intend a regexp match. + + Using `\n' in Bracket Expressions of Dynamic Regexps + + Some versions of `awk' do not allow the newline character to be used +inside a bracket expression for a dynamic regexp: + + $ awk '$0 ~ "[ \t\n]"' + error--> awk: newline in character class [ + error--> ]... + error--> source line number 1 + error--> context is + error--> >>> <<< + + But a newline in a regexp constant works with no problem: + + $ awk '$0 ~ /[ \t\n]/' + here is a sample line + -| here is a sample line + Ctrl-d + + `gawk' does not have this problem, and it isn't likely to occur +often in practice, but it's worth noting for future reference. + + +File: gawk.info, Node: GNU Regexp Operators, Next: Case-sensitivity, Prev: Computed Regexps, Up: Regexp + +3.7 `gawk'-Specific Regexp Operators ==================================== GNU software that deals with regular expressions provides a number of @@ -3812,9 +3926,9 @@ No options default. -File: gawk.info, Node: Case-sensitivity, Next: Leftmost Longest, Prev: GNU Regexp Operators, Up: Regexp +File: gawk.info, Node: Case-sensitivity, Next: Regexp Summary, Prev: GNU Regexp Operators, Up: Regexp -3.6 Case Sensitivity in Matching +3.8 Case Sensitivity in Matching ================================ Case is normally significant in regular expressions, both when matching @@ -3887,116 +4001,7 @@ obscure and we don't recommend it. means that `gawk' does the right thing. -File: gawk.info, Node: Leftmost Longest, Next: Computed Regexps, Prev: Case-sensitivity, Up: Regexp - -3.7 How Much Text Matches? -========================== - -Consider the following: - - echo aaaabcd | awk '{ sub(/a+/, "<A>"); print }' - - This example uses the `sub()' function (which we haven't discussed -yet; *note String Functions::) to make a change to the input record. -Here, the regexp `/a+/' indicates "one or more `a' characters," and the -replacement text is `<A>'. - - The input contains four `a' characters. `awk' (and POSIX) regular -expressions always match the leftmost, _longest_ sequence of input -characters that can match. Thus, all four `a' characters are replaced -with `<A>' in this example: - - $ echo aaaabcd | awk '{ sub(/a+/, "<A>"); print }' - -| <A>bcd - - For simple match/no-match tests, this is not so important. But when -doing text matching and substitutions with the `match()', `sub()', -`gsub()', and `gensub()' functions, it is very important. *Note String -Functions::, for more information on these functions. Understanding -this principle is also important for regexp-based record and field -splitting (*note Records::, and also *note Field Separators::). - - -File: gawk.info, Node: Computed Regexps, Next: Regexp Summary, Prev: Leftmost Longest, Up: Regexp - -3.8 Using Dynamic Regexps -========================= - -The righthand side of a `~' or `!~' operator need not be a regexp -constant (i.e., a string of characters between slashes). It may be any -expression. The expression is evaluated and converted to a string if -necessary; the contents of the string are then used as the regexp. A -regexp computed in this way is called a "dynamic regexp" or a "computed -regexp": - - BEGIN { digits_regexp = "[[:digit:]]+" } - $0 ~ digits_regexp { print } - -This sets `digits_regexp' to a regexp that describes one or more digits, -and tests whether the input record matches this regexp. - - NOTE: When using the `~' and `!~' operators, there is a difference - between a regexp constant enclosed in slashes and a string - constant enclosed in double quotes. If you are going to use a - string constant, you have to understand that the string is, in - essence, scanned _twice_: the first time when `awk' reads your - program, and the second time when it goes to match the string on - the lefthand side of the operator with the pattern on the right. - This is true of any string-valued expression (such as - `digits_regexp', shown previously), not just string constants. - - What difference does it make if the string is scanned twice? The -answer has to do with escape sequences, and particularly with -backslashes. To get a backslash into a regular expression inside a -string, you have to type two backslashes. - - For example, `/\*/' is a regexp constant for a literal `*'. Only -one backslash is needed. To do the same thing with a string, you have -to type `"\\*"'. The first backslash escapes the second one so that -the string actually contains the two characters `\' and `*'. - - Given that you can use both regexp and string constants to describe -regular expressions, which should you use? The answer is "regexp -constants," for several reasons: - - * String constants are more complicated to write and more difficult - to read. Using regexp constants makes your programs less - error-prone. Not understanding the difference between the two - kinds of constants is a common source of errors. - - * It is more efficient to use regexp constants. `awk' can note that - you have supplied a regexp and store it internally in a form that - makes pattern matching more efficient. When using a string - constant, `awk' must first convert the string into this internal - form and then perform the pattern matching. - - * Using regexp constants is better form; it shows clearly that you - intend a regexp match. - - Using `\n' in Bracket Expressions of Dynamic Regexps - - Some versions of `awk' do not allow the newline character to be used -inside a bracket expression for a dynamic regexp: - - $ awk '$0 ~ "[ \t\n]"' - error--> awk: newline in character class [ - error--> ]... - error--> source line number 1 - error--> context is - error--> >>> <<< - - But a newline in a regexp constant works with no problem: - - $ awk '$0 ~ /[ \t\n]/' - here is a sample line - -| here is a sample line - Ctrl-d - - `gawk' does not have this problem, and it isn't likely to occur -often in practice, but it's worth noting for future reference. - - -File: gawk.info, Node: Regexp Summary, Prev: Computed Regexps, Up: Regexp +File: gawk.info, Node: Regexp Summary, Prev: Case-sensitivity, Up: Regexp 3.9 Summary =========== @@ -5383,35 +5388,47 @@ input record and split it up into fields. This is useful if you've finished processing the current record, but want to do some special processing on the next record _right now_. For example: + # Remove text between /* and */, inclusive { - if ((t = index($0, "/*")) != 0) { - # value of `tmp' will be "" if t is 1 - tmp = substr($0, 1, t - 1) - u = index(substr($0, t + 2), "*/") - offset = t + 2 - while (u == 0) { - if (getline <= 0) { + if ((i = index($0, "/*")) != 0) { + out = substr($0, 1, i - 1) # leading part of the string + rest = substr($0, i + 2) # ... */ ... + j = index(rest, "*/") # is */ in trailing part? + if (j > 0) { + rest = substr(rest, j + 2) # remove comment + } else { + while (j == 0) { + # get more text + if (getline <= 0) { m = "unexpected EOF or error" m = (m ": " ERRNO) print m > "/dev/stderr" exit - } - u = index($0, "*/") - offset = 0 - } - # substr() expression will be "" if */ - # occurred at end of line - $0 = tmp substr($0, offset + u + 2) - } - print $0 + } + # build up the line using string concatenation + rest = rest $0 + j = index(rest, "*/") # is */ in trailing part? + if (j != 0) { + rest = substr(rest, j + 2) + break + } + } + } + # build up the output line using string concatenation + $0 = out rest + } + print $0 } This `awk' program deletes C-style comments (`/* ... */') from the -input. By replacing the `print $0' with other statements, you could -perform more complicated processing on the decommented input, such as -searching for matches of a regular expression. (This program has a -subtle problem--it does not work if one comment ends and another begins -on the same line.) +input. It uses a number of features we haven't covered yet, including +string concatenation (*note Concatenation::) and the `index()' and +`substr()' built-in functions (*note String Functions::). By replacing +the `print $0' with other statements, you could perform more +complicated processing on the decommented input, such as searching for +matches of a regular expression. (This program has a subtle +problem--it does not work if one comment ends and another begins on the +same line.) This form of the `getline' command sets `NF', `NR', `FNR', `RT', and the value of `$0'. @@ -5975,8 +5992,8 @@ File: gawk.info, Node: Input Exercises, Prev: Input Summary, Up: Reading File 2. *note Plain Getline::, presented a program to remove C-style comments (`/* ... */') from the input. That program does not work if one comment ends on one line and another one starts later on - the same line. Write a program that does handle multiple comments - on the line. + the same line. That can be fixed by making one simple change. + What is it? @@ -7307,8 +7324,9 @@ File: gawk.info, Node: Regexp Constants, Prev: Nondecimal-numbers, Up: Consta A regexp constant is a regular expression description enclosed in slashes, such as `/^beginning and end$/'. Most regexps used in `awk' programs are constant, but the `~' and `!~' matching operators can also -match computed or dynamic regexps (which are just ordinary strings or -variables that contain a regexp). +match computed or dynamic regexps (which are typically just ordinary +strings or variables that contain a regexp, but could be a more complex +expression). File: gawk.info, Node: Using Constant Regexps, Next: Variables, Prev: Constants, Up: Values @@ -8458,7 +8476,7 @@ following program is one way to print lines in between special bracketing lines: $1 == "START" { interested = ! interested; next } - interested == 1 { print } + interested { print } $1 == "END" { interested = ! interested; next } The variable `interested', as with all `awk' variables, starts out @@ -8468,6 +8486,14 @@ using `!'. The next rule prints lines as long as `interested' is true. When a line is seen whose first field is `END', `interested' is toggled back to false.(1) + Most commonly, the `!' operator is used in the conditions of `if' +and `while' statements, where it often makes more sense to phrase the +logic in the negative: + + if (! SOME CONDITION || SOME OTHER CONDITION) { + ... DO WHATEVER PROCESSING ... + } + NOTE: The `next' statement is discussed in *note Next Statement::. `next' tells `awk' to skip the rest of the rules, get the next record, and start processing the rules over again at the top. The @@ -9836,7 +9862,7 @@ reset to one, and processing starts over with the first rule in the program. If the `nextfile' statement causes the end of the input to be reached, then the code in any `END' rules is executed. An exception to this is when `nextfile' is invoked during execution of any statement in -an `END' rule; In this case, it causes the program to stop immediately. +an `END' rule; in this case, it causes the program to stop immediately. *Note BEGIN/END::. The `nextfile' statement is useful when there are many data files to @@ -9846,10 +9872,10 @@ would have to continue scanning the unwanted records. The `nextfile' statement accomplishes this much more efficiently. In `gawk', execution of `nextfile' causes additional things to -happen: any `ENDFILE' rules are executed except in the case as -mentioned below, `ARGIND' is incremented, and any `BEGINFILE' rules are -executed. (`ARGIND' hasn't been introduced yet. *Note Built-in -Variables::.) +happen: any `ENDFILE' rules are executed if `gawk' is not currently in +an `END' or `BEGINFILE' rule, `ARGIND' is incremented, and any +`BEGINFILE' rules are executed. (`ARGIND' hasn't been introduced yet. +*Note Built-in Variables::.) With `gawk', `nextfile' is useful inside a `BEGINFILE' rule to skip over a file that would otherwise cause `gawk' to exit with a fatal @@ -11283,7 +11309,7 @@ might look like this: > line 2 > line 3' | awk '{ l[lines] = $0; ++lines } > END { - > for (i = lines-1; i >= 0; --i) + > for (i = lines - 1; i >= 0; i--) > print l[i] > }' -| line 3 @@ -11304,7 +11330,7 @@ following version of the program works correctly: { l[lines++] = $0 } END { - for (i = lines - 1; i >= 0; --i) + for (i = lines - 1; i >= 0; i--) print l[i] } @@ -14396,8 +14422,9 @@ versions of `awk': ret = 0 for (i = 1; i <= n; i++) { c = substr(str, i, 1) - if ((k = index("01234567", c)) > 0) - k-- # adjust for 1-basing in awk + # index() returns 0 if c not in string, + # includes c == "0" + k = index("1234567", c) ret = ret * 8 + k } @@ -14409,6 +14436,8 @@ versions of `awk': for (i = 1; i <= n; i++) { c = substr(str, i, 1) c = tolower(c) + # index() returns 0 if c not in string, + # includes c == "0" k = index("123456789abcdef", c) ret = ret * 16 + k @@ -14869,7 +14898,7 @@ that might be as follows: This function reads from `file' one record at a time, building up the full contents of the file in the local variable `contents'. It -works, but is not necessarily efficient. +works, but is not necessarily efficient.(1) The following function, based on a suggestion by Denis Shirokov, reads the entire contents of the named file in one shot: @@ -14904,6 +14933,13 @@ string. Thus calling code may use something like: This tests the result to see if it is empty or not. An equivalent test would be `contents == ""'. + ---------- Footnotes ---------- + + (1) Execution time grows quadratically in the size of the input; for +each record, `awk' has to allocate a bigger internal buffer for +`contents', copy the old contents into it, and then append the contents +of the new record. + File: gawk.info, Node: Data File Management, Next: Getopt Function, Prev: General Functions, Up: Library Functions @@ -15357,8 +15393,7 @@ not an option, and it ends option processing. Continuing on: i = index(options, thisopt) if (i == 0) { if (Opterr) - printf("%c -- invalid option\n", - thisopt) > "/dev/stderr" + printf("%c -- invalid option\n", thisopt) > "/dev/stderr" if (_opti >= length(argv[Optind])) { Optind++ _opti = 0 @@ -30982,10 +31017,9 @@ Index * ! (exclamation point), !~ operator <3>: Comparison Operators. (line 11) * ! (exclamation point), !~ operator <4>: Regexp Constants. (line 6) -* ! (exclamation point), !~ operator <5>: Computed Regexps. (line 6) -* ! (exclamation point), !~ operator <6>: Case-sensitivity. (line 26) +* ! (exclamation point), !~ operator <5>: Case-sensitivity. (line 26) +* ! (exclamation point), !~ operator <6>: Computed Regexps. (line 6) * ! (exclamation point), !~ operator: Regexp Usage. (line 19) -* " (double quote) in shell commands: Read Terminal. (line 25) * " (double quote), in regexp constants: Computed Regexps. (line 29) * " (double quote), in shell commands: Quoting. (line 54) * # (number sign), #! (executable scripts): Executable Scripts. @@ -31173,8 +31207,7 @@ Index * ? (question mark), regexp operator: Regexp Operators. (line 111) * [] (square brackets), regexp operator: Regexp Operators. (line 56) * \ (backslash): Comments. (line 50) -* \ (backslash) in shell commands: Read Terminal. (line 25) -* \ (backslash), \" escape sequence: Escape Sequences. (line 82) +* \ (backslash), \" escape sequence: Escape Sequences. (line 84) * \ (backslash), \' operator (gawk): GNU Regexp Operators. (line 56) * \ (backslash), \/ escape sequence: Escape Sequences. (line 75) @@ -31217,7 +31250,7 @@ Index * \ (backslash), in bracket expressions: Bracket Expressions. (line 17) * \ (backslash), in escape sequences: Escape Sequences. (line 6) * \ (backslash), in escape sequences, POSIX and: Escape Sequences. - (line 118) + (line 120) * \ (backslash), in regexp constants: Computed Regexps. (line 29) * \ (backslash), in shell commands: Quoting. (line 48) * \ (backslash), regexp operator: Regexp Operators. (line 18) @@ -31444,8 +31477,7 @@ Index * awkvars.out file: Options. (line 93) * b debugger command (alias for break): Breakpoint Control. (line 11) * backslash (\): Comments. (line 50) -* backslash (\) in shell commands: Read Terminal. (line 25) -* backslash (\), \" escape sequence: Escape Sequences. (line 82) +* backslash (\), \" escape sequence: Escape Sequences. (line 84) * backslash (\), \' operator (gawk): GNU Regexp Operators. (line 56) * backslash (\), \/ escape sequence: Escape Sequences. (line 75) @@ -31488,7 +31520,7 @@ Index * backslash (\), in bracket expressions: Bracket Expressions. (line 17) * backslash (\), in escape sequences: Escape Sequences. (line 6) * backslash (\), in escape sequences, POSIX and: Escape Sequences. - (line 118) + (line 120) * backslash (\), in regexp constants: Computed Regexps. (line 29) * backslash (\), in shell commands: Quoting. (line 48) * backslash (\), regexp operator: Regexp Operators. (line 18) @@ -31593,7 +31625,7 @@ Index (line 67) * Brian Kernighan's awk <12>: GNU Regexp Operators. (line 83) -* Brian Kernighan's awk <13>: Escape Sequences. (line 122) +* Brian Kernighan's awk <13>: Escape Sequences. (line 124) * Brian Kernighan's awk: When. (line 21) * Brian Kernighan's awk, extensions: BTL. (line 6) * Brian Kernighan's awk, source code: Other Versions. (line 13) @@ -31621,6 +31653,7 @@ Index * built-in variables, conveying information: Auto-set. (line 6) * built-in variables, user-modifiable: User-modified. (line 6) * Busybox Awk: Other Versions. (line 88) +* c.e., See common extensions: Conventions. (line 51) * call by reference: Pass By Value/Reference. (line 47) * call by value: Pass By Value/Reference. @@ -31819,9 +31852,9 @@ Index * dark corner, command-line arguments: Assignment Options. (line 43) * dark corner, continue statement: Continue Statement. (line 44) * dark corner, CONVFMT variable: Strings And Numbers. (line 40) -* dark corner, escape sequences: Other Arguments. (line 31) +* dark corner, escape sequences: Other Arguments. (line 35) * dark corner, escape sequences, for metacharacters: Escape Sequences. - (line 140) + (line 142) * dark corner, exit statement: Exit Statement. (line 30) * dark corner, field separators: Field Splitting Summary. (line 46) @@ -32087,7 +32120,6 @@ Index * dollar sign ($), incrementing fields and arrays: Increment Ops. (line 30) * dollar sign ($), regexp operator: Regexp Operators. (line 35) -* double quote (") in shell commands: Read Terminal. (line 25) * double quote ("), in regexp constants: Computed Regexps. (line 29) * double quote ("), in shell commands: Quoting. (line 54) * down debugger command: Execution Stack. (line 21) @@ -32187,8 +32219,8 @@ Index * exclamation point (!), !~ operator <3>: Comparison Operators. (line 11) * exclamation point (!), !~ operator <4>: Regexp Constants. (line 6) -* exclamation point (!), !~ operator <5>: Computed Regexps. (line 6) -* exclamation point (!), !~ operator <6>: Case-sensitivity. (line 26) +* exclamation point (!), !~ operator <5>: Case-sensitivity. (line 26) +* exclamation point (!), !~ operator <6>: Computed Regexps. (line 6) * exclamation point (!), !~ operator: Regexp Usage. (line 19) * exit statement: Exit Statement. (line 6) * exit status, of gawk: Exit Status. (line 6) @@ -32196,7 +32228,7 @@ Index * exit the debugger: Miscellaneous Debugger Commands. (line 99) * exp: Numeric Functions. (line 33) -* expand utility: Very Simple. (line 69) +* expand utility: Very Simple. (line 72) * Expat XML parser library: gawkextlib. (line 35) * exponent: Numeric Functions. (line 33) * expressions: Expressions. (line 6) @@ -32330,7 +32362,7 @@ Index (line 47) * files, message object, specifying directory of: Explaining gettext. (line 54) -* files, multiple passes over: Other Arguments. (line 49) +* files, multiple passes over: Other Arguments. (line 53) * files, multiple, duplicating output into: Tee Program. (line 6) * files, output, See output files: Close Files And Pipes. (line 6) @@ -32491,7 +32523,7 @@ Index * gawk, ERRNO variable in <4>: Close Files And Pipes. (line 139) * gawk, ERRNO variable in: Getline. (line 19) -* gawk, escape sequences: Escape Sequences. (line 130) +* gawk, escape sequences: Escape Sequences. (line 132) * gawk, extensions, disabling: Options. (line 252) * gawk, features, adding: Adding Code. (line 6) * gawk, features, advanced: Advanced Features. (line 6) @@ -32715,7 +32747,7 @@ Index * input files, examples: Sample Data Files. (line 6) * input files, reading: Reading Files. (line 6) * input files, running awk without: Read Terminal. (line 6) -* input files, variable assignments and: Other Arguments. (line 19) +* input files, variable assignments and: Other Arguments. (line 23) * input pipeline: Getline/Pipe. (line 9) * input record, length of: String Functions. (line 174) * input redirection: Getline/File. (line 6) @@ -32924,7 +32956,7 @@ Index * mawk utility <2>: Nextfile Statement. (line 47) * mawk utility <3>: Concatenation. (line 36) * mawk utility <4>: Getline/Pipe. (line 62) -* mawk utility: Escape Sequences. (line 130) +* mawk utility: Escape Sequences. (line 132) * maximum precision supported by MPFR library: Auto-set. (line 221) * McIlroy, Doug: Glossary. (line 149) * McPhee, Patrick: Contributors. (line 100) @@ -32937,7 +32969,7 @@ Index (line 54) * messages from extensions: Printing Messages. (line 6) * metacharacters in regular expressions: Regexp Operators. (line 6) -* metacharacters, escape sequences for: Escape Sequences. (line 136) +* metacharacters, escape sequences for: Escape Sequences. (line 138) * minimum precision supported by MPFR library: Auto-set. (line 224) * mktime: Time Functions. (line 25) * modifiers, in format specifiers: Format Modifiers. (line 6) @@ -32975,7 +33007,7 @@ Index (line 43) * next file statement: Feature History. (line 169) * next statement <1>: Next Statement. (line 6) -* next statement: Boolean Ops. (line 85) +* next statement: Boolean Ops. (line 93) * next statement, BEGIN/END patterns and: I/O And BEGIN/END. (line 36) * next statement, BEGINFILE/ENDFILE patterns and: BEGINFILE/ENDFILE. (line 49) @@ -33156,14 +33188,14 @@ Index * plus sign (+), += operator: Assignment Ops. (line 82) * plus sign (+), regexp operator: Regexp Operators. (line 105) * pointers to functions: Indirect Calls. (line 6) -* portability: Escape Sequences. (line 100) +* portability: Escape Sequences. (line 102) * portability, #! (executable scripts): Executable Scripts. (line 33) * portability, ** operator and: Arithmetic Ops. (line 81) * portability, **= operator and: Assignment Ops. (line 143) * portability, ARGV variable: Executable Scripts. (line 59) * portability, backslash continuation and: Statements/Lines. (line 30) * portability, backslash in escape sequences: Escape Sequences. - (line 118) + (line 120) * portability, close() function and: Close Files And Pipes. (line 81) * portability, data files as single record: gawk split records. @@ -33202,7 +33234,7 @@ Index * POSIX awk, < operator and: Getline/File. (line 26) * POSIX awk, arithmetic operators and: Arithmetic Ops. (line 30) * POSIX awk, backslashes in string constants: Escape Sequences. - (line 118) + (line 120) * POSIX awk, BEGIN/END patterns: I/O And BEGIN/END. (line 16) * POSIX awk, bracket expressions and: Bracket Expressions. (line 26) * POSIX awk, bracket expressions and, character classes: Bracket Expressions. @@ -33546,7 +33578,6 @@ Index * set watchpoint: Viewing And Changing Data. (line 67) * shadowing of variable values: Definition Syntax. (line 70) -* shell quoting, double quote: Read Terminal. (line 25) * shell quoting, rules for: Quoting. (line 6) * shells, piping commands into: Redirection. (line 142) * shells, quoting: Using Shell Variables. @@ -33583,14 +33614,14 @@ Index * sidebar, A Constant's Base Does Not Affect Its Value: Nondecimal-numbers. (line 64) * sidebar, Backslash Before Regular Characters: Escape Sequences. - (line 116) + (line 118) * sidebar, Changing FS Does Not Affect the Fields: Field Splitting Summary. (line 38) * sidebar, Changing NR and FNR: Auto-set. (line 307) * sidebar, Controlling Output Buffering with system(): I/O Functions. (line 138) * sidebar, Escape Sequences for Metacharacters: Escape Sequences. - (line 134) + (line 136) * sidebar, FS and IGNORECASE: Field Splitting Summary. (line 64) * sidebar, Interactive Versus Noninteractive Buffering: I/O Functions. @@ -33790,8 +33821,8 @@ Index * tilde (~), ~ operator <3>: Comparison Operators. (line 11) * tilde (~), ~ operator <4>: Regexp Constants. (line 6) -* tilde (~), ~ operator <5>: Computed Regexps. (line 6) -* tilde (~), ~ operator <6>: Case-sensitivity. (line 26) +* tilde (~), ~ operator <5>: Case-sensitivity. (line 26) +* tilde (~), ~ operator <6>: Computed Regexps. (line 6) * tilde (~), ~ operator: Regexp Usage. (line 19) * time functions: Time Functions. (line 6) * time, alarm clock example program: Alarm Program. (line 11) @@ -33818,7 +33849,7 @@ Index (line 37) * troubleshooting, awk uses FS not IFS: Field Separators. (line 30) * troubleshooting, backslash before nonspecial character: Escape Sequences. - (line 118) + (line 120) * troubleshooting, division: Arithmetic Ops. (line 44) * troubleshooting, fatal errors, field widths, specifying: Constant Size. (line 23) @@ -33874,7 +33905,7 @@ Index * uniq.awk program: Uniq Program. (line 65) * Unix: Glossary. (line 611) * Unix awk, backslashes in escape sequences: Escape Sequences. - (line 130) + (line 132) * Unix awk, close() function and: Close Files And Pipes. (line 131) * Unix awk, password files, field separators and: Command Line Field Separator. @@ -33897,7 +33928,7 @@ Index * USR1 signal, for dynamic profiling: Profiling. (line 188) * values, numeric: Basic Data Typing. (line 13) * values, string: Basic Data Typing. (line 13) -* variable assignments and input files: Other Arguments. (line 19) +* variable assignments and input files: Other Arguments. (line 23) * variable typing: Typing and Comparison. (line 9) * variables <1>: Basic Data Typing. (line 6) @@ -34011,8 +34042,8 @@ Index * ~ (tilde), ~ operator <3>: Comparison Operators. (line 11) * ~ (tilde), ~ operator <4>: Regexp Constants. (line 6) -* ~ (tilde), ~ operator <5>: Computed Regexps. (line 6) -* ~ (tilde), ~ operator <6>: Case-sensitivity. (line 26) +* ~ (tilde), ~ operator <5>: Case-sensitivity. (line 26) +* ~ (tilde), ~ operator <6>: Computed Regexps. (line 6) * ~ (tilde), ~ operator: Regexp Usage. (line 19) @@ -34038,533 +34069,533 @@ Node: Getting Started70581 Node: Running gawk73015 Node: One-shot74205 Node: Read Terminal75430 -Ref: Read Terminal-Footnote-177393 -Node: Long77564 -Node: Executable Scripts78958 -Ref: Executable Scripts-Footnote-181759 -Node: Comments81861 -Node: Quoting84334 -Node: DOS Quoting89647 -Node: Sample Data Files90322 -Node: Very Simple92929 -Node: Two Rules97688 -Node: More Complex99582 -Ref: More Complex-Footnote-1102496 -Node: Statements/Lines102581 -Ref: Statements/Lines-Footnote-1107037 -Node: Other Features107302 -Node: When108230 -Ref: When-Footnote-1109986 -Node: Intro Summary110051 -Node: Invoking Gawk110934 -Node: Command Line112449 -Node: Options113240 -Ref: Options-Footnote-1128887 -Node: Other Arguments128912 -Node: Naming Standard Input131574 -Node: Environment Variables132667 -Node: AWKPATH Variable133225 -Ref: AWKPATH Variable-Footnote-1136091 -Ref: AWKPATH Variable-Footnote-2136136 -Node: AWKLIBPATH Variable136396 -Node: Other Environment Variables137155 -Node: Exit Status140607 -Node: Include Files141282 -Node: Loading Shared Libraries144860 -Node: Obsolete146244 -Node: Undocumented146941 -Node: Invoking Summary147208 -Node: Regexp148808 -Node: Regexp Usage150267 -Node: Escape Sequences152300 -Node: Regexp Operators158200 -Ref: Regexp Operators-Footnote-1165631 -Ref: Regexp Operators-Footnote-2165778 -Node: Bracket Expressions165876 -Ref: table-char-classes167898 -Node: GNU Regexp Operators170838 -Node: Case-sensitivity174547 -Ref: Case-sensitivity-Footnote-1177439 -Ref: Case-sensitivity-Footnote-2177674 -Node: Leftmost Longest177782 -Node: Computed Regexps178983 -Node: Regexp Summary182355 -Node: Reading Files183824 -Node: Records185916 -Node: awk split records186638 -Node: gawk split records191496 -Ref: gawk split records-Footnote-1196017 -Node: Fields196054 -Ref: Fields-Footnote-1199018 -Node: Nonconstant Fields199104 -Ref: Nonconstant Fields-Footnote-1201334 -Node: Changing Fields201536 -Node: Field Separators207490 -Node: Default Field Splitting210192 -Node: Regexp Field Splitting211309 -Node: Single Character Fields214636 -Node: Command Line Field Separator215695 -Node: Full Line Fields219121 -Ref: Full Line Fields-Footnote-1219629 -Node: Field Splitting Summary219675 -Ref: Field Splitting Summary-Footnote-1222807 -Node: Constant Size222908 -Node: Splitting By Content227514 -Ref: Splitting By Content-Footnote-1231587 -Node: Multiple Line231627 -Ref: Multiple Line-Footnote-1237483 -Node: Getline237662 -Node: Plain Getline239873 -Node: Getline/Variable241968 -Node: Getline/File243115 -Node: Getline/Variable/File244499 -Ref: Getline/Variable/File-Footnote-1246098 -Node: Getline/Pipe246185 -Node: Getline/Variable/Pipe248871 -Node: Getline/Coprocess249978 -Node: Getline/Variable/Coprocess251230 -Node: Getline Notes251967 -Node: Getline Summary254771 -Ref: table-getline-variants255179 -Node: Read Timeout256091 -Ref: Read Timeout-Footnote-1259918 -Node: Command-line directories259976 -Node: Input Summary260880 -Node: Input Exercises264017 -Node: Printing264750 -Node: Print266472 -Node: Print Examples267965 -Node: Output Separators270744 -Node: OFMT272760 -Node: Printf274118 -Node: Basic Printf275024 -Node: Control Letters276563 -Node: Format Modifiers280554 -Node: Printf Examples286581 -Node: Redirection289045 -Node: Special Files296017 -Node: Special FD296550 -Ref: Special FD-Footnote-1300147 -Node: Special Network300221 -Node: Special Caveats301071 -Node: Close Files And Pipes301867 -Ref: Close Files And Pipes-Footnote-1309028 -Ref: Close Files And Pipes-Footnote-2309176 -Node: Output Summary309326 -Node: Output Exercises310323 -Node: Expressions311003 -Node: Values312188 -Node: Constants312864 -Node: Scalar Constants313544 -Ref: Scalar Constants-Footnote-1314403 -Node: Nondecimal-numbers314653 -Node: Regexp Constants317653 -Node: Using Constant Regexps318128 -Node: Variables321200 -Node: Using Variables321855 -Node: Assignment Options323579 -Node: Conversion325454 -Node: Strings And Numbers325978 -Ref: Strings And Numbers-Footnote-1329040 -Node: Locale influences conversions329149 -Ref: table-locale-affects331866 -Node: All Operators332454 -Node: Arithmetic Ops333084 -Node: Concatenation335589 -Ref: Concatenation-Footnote-1338408 -Node: Assignment Ops338514 -Ref: table-assign-ops343497 -Node: Increment Ops344800 -Node: Truth Values and Conditions348238 -Node: Truth Values349321 -Node: Typing and Comparison350370 -Node: Variable Typing351163 -Node: Comparison Operators354815 -Ref: table-relational-ops355225 -Node: POSIX String Comparison358775 -Ref: POSIX String Comparison-Footnote-1359859 -Node: Boolean Ops359997 -Ref: Boolean Ops-Footnote-1364072 -Node: Conditional Exp364163 -Node: Function Calls365890 -Node: Precedence369770 -Node: Locales373439 -Node: Expressions Summary375070 -Node: Patterns and Actions377611 -Node: Pattern Overview378727 -Node: Regexp Patterns380404 -Node: Expression Patterns380947 -Node: Ranges384727 -Node: BEGIN/END387833 -Node: Using BEGIN/END388595 -Ref: Using BEGIN/END-Footnote-1391331 -Node: I/O And BEGIN/END391437 -Node: BEGINFILE/ENDFILE393708 -Node: Empty396639 -Node: Using Shell Variables396956 -Node: Action Overview399239 -Node: Statements401566 -Node: If Statement403414 -Node: While Statement404912 -Node: Do Statement406956 -Node: For Statement408112 -Node: Switch Statement411264 -Node: Break Statement413652 -Node: Continue Statement415693 -Node: Next Statement417518 -Node: Nextfile Statement419908 -Node: Exit Statement422544 -Node: Built-in Variables424948 -Node: User-modified426075 -Ref: User-modified-Footnote-1433764 -Node: Auto-set433826 -Ref: Auto-set-Footnote-1446745 -Ref: Auto-set-Footnote-2446950 -Node: ARGC and ARGV447006 -Node: Pattern Action Summary450910 -Node: Arrays453133 -Node: Array Basics454682 -Node: Array Intro455508 -Ref: figure-array-elements457481 -Ref: Array Intro-Footnote-1460005 -Node: Reference to Elements460133 -Node: Assigning Elements462583 -Node: Array Example463074 -Node: Scanning an Array464806 -Node: Controlling Scanning467807 -Ref: Controlling Scanning-Footnote-1472980 -Node: Delete473296 -Ref: Delete-Footnote-1476047 -Node: Numeric Array Subscripts476104 -Node: Uninitialized Subscripts478287 -Node: Multidimensional479912 -Node: Multiscanning483025 -Node: Arrays of Arrays484614 -Node: Arrays Summary489277 -Node: Functions491382 -Node: Built-in492255 -Node: Calling Built-in493333 -Node: Numeric Functions495321 -Ref: Numeric Functions-Footnote-1500157 -Ref: Numeric Functions-Footnote-2500514 -Ref: Numeric Functions-Footnote-3500562 -Node: String Functions500831 -Ref: String Functions-Footnote-1523828 -Ref: String Functions-Footnote-2523957 -Ref: String Functions-Footnote-3524205 -Node: Gory Details524292 -Ref: table-sub-escapes526065 -Ref: table-sub-proposed527585 -Ref: table-posix-sub528949 -Ref: table-gensub-escapes530489 -Ref: Gory Details-Footnote-1531665 -Node: I/O Functions531816 -Ref: I/O Functions-Footnote-1538926 -Node: Time Functions539073 -Ref: Time Functions-Footnote-1549537 -Ref: Time Functions-Footnote-2549605 -Ref: Time Functions-Footnote-3549763 -Ref: Time Functions-Footnote-4549874 -Ref: Time Functions-Footnote-5549986 -Ref: Time Functions-Footnote-6550213 -Node: Bitwise Functions550479 -Ref: table-bitwise-ops551041 -Ref: Bitwise Functions-Footnote-1555286 -Node: Type Functions555470 -Node: I18N Functions556612 -Node: User-defined558257 -Node: Definition Syntax559061 -Ref: Definition Syntax-Footnote-1564374 -Node: Function Example564443 -Ref: Function Example-Footnote-1567083 -Node: Function Caveats567105 -Node: Calling A Function567623 -Node: Variable Scope568578 -Node: Pass By Value/Reference571566 -Node: Return Statement575076 -Node: Dynamic Typing578060 -Node: Indirect Calls578989 -Node: Functions Summary588702 -Node: Library Functions591241 -Ref: Library Functions-Footnote-1594859 -Ref: Library Functions-Footnote-2595002 -Node: Library Names595173 -Ref: Library Names-Footnote-1598646 -Ref: Library Names-Footnote-2598866 -Node: General Functions598952 -Node: Strtonum Function599980 -Node: Assert Function602760 -Node: Round Function606086 -Node: Cliff Random Function607627 -Node: Ordinal Functions608643 -Ref: Ordinal Functions-Footnote-1611708 -Ref: Ordinal Functions-Footnote-2611960 -Node: Join Function612171 -Ref: Join Function-Footnote-1613942 -Node: Getlocaltime Function614142 -Node: Readfile Function617878 -Node: Data File Management619717 -Node: Filetrans Function620349 -Node: Rewind Function624418 -Node: File Checking625976 -Ref: File Checking-Footnote-1627108 -Node: Empty Files627309 -Node: Ignoring Assigns629288 -Node: Getopt Function630842 -Ref: Getopt Function-Footnote-1642145 -Node: Passwd Functions642348 -Ref: Passwd Functions-Footnote-1651327 -Node: Group Functions651415 -Ref: Group Functions-Footnote-1659346 -Node: Walking Arrays659559 -Node: Library Functions Summary661162 -Node: Library Exercises662550 -Node: Sample Programs663830 -Node: Running Examples664600 -Node: Clones665328 -Node: Cut Program666552 -Node: Egrep Program676410 -Ref: Egrep Program-Footnote-1683997 -Node: Id Program684107 -Node: Split Program687761 -Ref: Split Program-Footnote-1691299 -Node: Tee Program691427 -Node: Uniq Program694214 -Node: Wc Program701635 -Ref: Wc Program-Footnote-1705900 -Node: Miscellaneous Programs705992 -Node: Dupword Program707205 -Node: Alarm Program709236 -Node: Translate Program714040 -Ref: Translate Program-Footnote-1718431 -Ref: Translate Program-Footnote-2718701 -Node: Labels Program718835 -Ref: Labels Program-Footnote-1722196 -Node: Word Sorting722280 -Node: History Sorting726323 -Node: Extract Program728159 -Node: Simple Sed735695 -Node: Igawk Program738757 -Ref: Igawk Program-Footnote-1753061 -Ref: Igawk Program-Footnote-2753262 -Node: Anagram Program753400 -Node: Signature Program756468 -Node: Programs Summary757715 -Node: Programs Exercises758930 -Node: Advanced Features762581 -Node: Nondecimal Data764529 -Node: Array Sorting766106 -Node: Controlling Array Traversal766803 -Node: Array Sorting Functions775083 -Ref: Array Sorting Functions-Footnote-1778990 -Node: Two-way I/O779184 -Ref: Two-way I/O-Footnote-1784128 -Ref: Two-way I/O-Footnote-2784307 -Node: TCP/IP Networking784389 -Node: Profiling787234 -Node: Advanced Features Summary794785 -Node: Internationalization796649 -Node: I18N and L10N798129 -Node: Explaining gettext798815 -Ref: Explaining gettext-Footnote-1803841 -Ref: Explaining gettext-Footnote-2804025 -Node: Programmer i18n804190 -Ref: Programmer i18n-Footnote-1808984 -Node: Translator i18n809033 -Node: String Extraction809827 -Ref: String Extraction-Footnote-1810960 -Node: Printf Ordering811046 -Ref: Printf Ordering-Footnote-1813828 -Node: I18N Portability813892 -Ref: I18N Portability-Footnote-1816341 -Node: I18N Example816404 -Ref: I18N Example-Footnote-1819110 -Node: Gawk I18N819182 -Node: I18N Summary819820 -Node: Debugger821159 -Node: Debugging822181 -Node: Debugging Concepts822622 -Node: Debugging Terms824478 -Node: Awk Debugging827075 -Node: Sample Debugging Session827967 -Node: Debugger Invocation828487 -Node: Finding The Bug829820 -Node: List of Debugger Commands836302 -Node: Breakpoint Control837634 -Node: Debugger Execution Control841298 -Node: Viewing And Changing Data844658 -Node: Execution Stack848016 -Node: Debugger Info849529 -Node: Miscellaneous Debugger Commands853523 -Node: Readline Support858707 -Node: Limitations859599 -Node: Debugging Summary861873 -Node: Arbitrary Precision Arithmetic863041 -Node: Computer Arithmetic864528 -Ref: Computer Arithmetic-Footnote-1868915 -Node: Math Definitions868972 -Ref: table-ieee-formats872261 -Ref: Math Definitions-Footnote-1872801 -Node: MPFR features872904 -Node: FP Math Caution874521 -Ref: FP Math Caution-Footnote-1875571 -Node: Inexactness of computations875940 -Node: Inexact representation876888 -Node: Comparing FP Values878243 -Node: Errors accumulate879207 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-Ref: Memory Allocation Functions-Footnote-1925858 -Node: Constructor Functions925954 -Node: Registration Functions927712 -Node: Extension Functions928397 -Node: Exit Callback Functions930699 -Node: Extension Version String931947 -Node: Input Parsers932597 -Node: Output Wrappers942411 -Node: Two-way processors946927 -Node: Printing Messages949131 -Ref: Printing Messages-Footnote-1950208 -Node: Updating `ERRNO'950360 -Node: Accessing Parameters951099 -Node: Symbol Table Access952329 -Node: Symbol table by name952843 -Node: Symbol table by cookie954819 -Ref: Symbol table by cookie-Footnote-1958952 -Node: Cached values959015 -Ref: Cached values-Footnote-1962519 -Node: Array Manipulation962610 -Ref: Array Manipulation-Footnote-1963708 -Node: Array Data Types963747 -Ref: Array Data Types-Footnote-1966450 -Node: Array Functions966542 -Node: Flattening Arrays970416 -Node: Creating Arrays977268 -Node: Extension API Variables981999 -Node: Extension Versioning982635 -Node: Extension API 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Group Functions653034 +Ref: Group Functions-Footnote-1660965 +Node: Walking Arrays661178 +Node: Library Functions Summary662781 +Node: Library Exercises664169 +Node: Sample Programs665449 +Node: Running Examples666219 +Node: Clones666947 +Node: Cut Program668171 +Node: Egrep Program678029 +Ref: Egrep Program-Footnote-1685616 +Node: Id Program685726 +Node: Split Program689380 +Ref: Split Program-Footnote-1692918 +Node: Tee Program693046 +Node: Uniq Program695833 +Node: Wc Program703254 +Ref: Wc Program-Footnote-1707519 +Node: Miscellaneous Programs707611 +Node: Dupword Program708824 +Node: Alarm Program710855 +Node: Translate Program715659 +Ref: Translate Program-Footnote-1720050 +Ref: Translate Program-Footnote-2720320 +Node: Labels Program720454 +Ref: Labels Program-Footnote-1723815 +Node: Word Sorting723899 +Node: History Sorting727942 +Node: Extract Program729778 +Node: Simple Sed737314 +Node: Igawk Program740376 +Ref: Igawk Program-Footnote-1754680 +Ref: Igawk Program-Footnote-2754881 +Node: Anagram Program755019 +Node: Signature Program758087 +Node: Programs Summary759334 +Node: Programs Exercises760549 +Node: Advanced Features764200 +Node: Nondecimal Data766148 +Node: Array Sorting767725 +Node: Controlling Array Traversal768422 +Node: Array Sorting Functions776702 +Ref: Array Sorting Functions-Footnote-1780609 +Node: Two-way I/O780803 +Ref: Two-way I/O-Footnote-1785747 +Ref: Two-way I/O-Footnote-2785926 +Node: TCP/IP Networking786008 +Node: Profiling788853 +Node: Advanced Features Summary796404 +Node: Internationalization798268 +Node: I18N and L10N799748 +Node: Explaining gettext800434 +Ref: Explaining gettext-Footnote-1805460 +Ref: Explaining gettext-Footnote-2805644 +Node: Programmer i18n805809 +Ref: Programmer i18n-Footnote-1810603 +Node: Translator i18n810652 +Node: String Extraction811446 +Ref: String Extraction-Footnote-1812579 +Node: Printf Ordering812665 +Ref: Printf Ordering-Footnote-1815447 +Node: I18N Portability815511 +Ref: I18N Portability-Footnote-1817960 +Node: I18N Example818023 +Ref: I18N Example-Footnote-1820729 +Node: Gawk I18N820801 +Node: I18N Summary821439 +Node: Debugger822778 +Node: Debugging823800 +Node: Debugging Concepts824241 +Node: Debugging Terms826097 +Node: Awk Debugging828694 +Node: Sample Debugging Session829586 +Node: Debugger Invocation830106 +Node: Finding The Bug831439 +Node: List of Debugger Commands837921 +Node: Breakpoint Control839253 +Node: Debugger Execution Control842917 +Node: Viewing And Changing Data846277 +Node: Execution Stack849635 +Node: Debugger Info851148 +Node: Miscellaneous Debugger Commands855142 +Node: Readline Support860326 +Node: Limitations861218 +Node: Debugging Summary863492 +Node: Arbitrary Precision Arithmetic864660 +Node: Computer Arithmetic866147 +Ref: Computer Arithmetic-Footnote-1870534 +Node: Math Definitions870591 +Ref: table-ieee-formats873880 +Ref: Math Definitions-Footnote-1874420 +Node: MPFR features874523 +Node: FP Math Caution876140 +Ref: FP Math Caution-Footnote-1877190 +Node: Inexactness of computations877559 +Node: Inexact representation878507 +Node: Comparing FP Values879862 +Node: Errors accumulate880826 +Node: Getting Accuracy882259 +Node: Try To Round884918 +Node: Setting precision885817 +Ref: table-predefined-precision-strings886499 +Node: Setting the rounding mode888292 +Ref: table-gawk-rounding-modes888656 +Ref: Setting the rounding mode-Footnote-1892110 +Node: Arbitrary Precision Integers892289 +Ref: Arbitrary Precision Integers-Footnote-1896062 +Node: POSIX Floating Point Problems896211 +Ref: POSIX Floating Point Problems-Footnote-1900087 +Node: Floating point summary900125 +Node: Dynamic Extensions902329 +Node: Extension Intro903881 +Node: Plugin License905146 +Node: Extension Mechanism Outline905831 +Ref: figure-load-extension906255 +Ref: figure-load-new-function907740 +Ref: figure-call-new-function908742 +Node: Extension API Description910726 +Node: Extension API Functions Introduction912176 +Node: General Data Types917043 +Ref: General Data Types-Footnote-1922736 +Node: Requesting Values923035 +Ref: table-value-types-returned923772 +Node: Memory Allocation Functions924730 +Ref: Memory Allocation Functions-Footnote-1927477 +Node: Constructor Functions927573 +Node: Registration Functions929331 +Node: Extension Functions930016 +Node: Exit Callback Functions932318 +Node: Extension Version String933566 +Node: Input Parsers934216 +Node: Output Wrappers944030 +Node: Two-way processors948546 +Node: Printing Messages950750 +Ref: Printing Messages-Footnote-1951827 +Node: Updating `ERRNO'951979 +Node: Accessing Parameters952718 +Node: Symbol Table Access953948 +Node: Symbol table by name954462 +Node: Symbol table by cookie956438 +Ref: Symbol table by cookie-Footnote-1960571 +Node: Cached values960634 +Ref: Cached values-Footnote-1964138 +Node: Array Manipulation964229 +Ref: Array Manipulation-Footnote-1965327 +Node: Array Data Types965366 +Ref: Array Data Types-Footnote-1968069 +Node: Array Functions968161 +Node: Flattening Arrays972035 +Node: Creating Arrays978887 +Node: Extension API Variables983618 +Node: Extension Versioning984254 +Node: Extension API Informational Variables986155 +Node: Extension API Boilerplate987241 +Node: Finding Extensions991045 +Node: Extension Example991605 +Node: Internal File Description992335 +Node: Internal File Ops996426 +Ref: Internal File Ops-Footnote-11007858 +Node: Using Internal File Ops1007998 +Ref: Using Internal File Ops-Footnote-11010345 +Node: Extension Samples1010613 +Node: Extension Sample File Functions1012137 +Node: Extension Sample Fnmatch1019705 +Node: Extension Sample Fork1021187 +Node: Extension Sample Inplace1022400 +Node: Extension Sample Ord1024075 +Node: Extension Sample Readdir1024911 +Ref: table-readdir-file-types1025767 +Node: Extension Sample Revout1026566 +Node: Extension Sample Rev2way1027157 +Node: Extension Sample Read write array1027898 +Node: Extension Sample Readfile1029777 +Node: Extension Sample API Tests1030877 +Node: Extension Sample Time1031402 +Node: gawkextlib1032717 +Node: Extension summary1035530 +Node: Extension Exercises1039223 +Node: Language History1039945 +Node: V7/SVR3.11041588 +Node: SVR41043908 +Node: POSIX1045350 +Node: BTL1046736 +Node: POSIX/GNU1047470 +Node: Feature History1053246 +Node: Common Extensions1066337 +Node: Ranges and Locales1067649 +Ref: Ranges and Locales-Footnote-11072266 +Ref: Ranges and Locales-Footnote-21072293 +Ref: Ranges and Locales-Footnote-31072527 +Node: Contributors1072748 +Node: History summary1078173 +Node: Installation1079542 +Node: Gawk Distribution1080493 +Node: Getting1080977 +Node: Extracting1081801 +Node: Distribution contents1083443 +Node: Unix Installation1089213 +Node: Quick Installation1089830 +Node: Additional Configuration Options1092272 +Node: Configuration Philosophy1094010 +Node: Non-Unix Installation1096361 +Node: PC Installation1096819 +Node: PC Binary Installation1098130 +Node: PC Compiling1099978 +Ref: PC Compiling-Footnote-11102977 +Node: PC Testing1103082 +Node: PC Using1104258 +Node: Cygwin1108410 +Node: MSYS1109219 +Node: VMS Installation1109733 +Node: VMS Compilation1110529 +Ref: VMS Compilation-Footnote-11111751 +Node: VMS Dynamic Extensions1111809 +Node: VMS Installation Details1113182 +Node: VMS Running1115434 +Node: VMS GNV1118268 +Node: VMS Old Gawk1118991 +Node: Bugs1119461 +Node: Other Versions1123465 +Node: Installation summary1129692 +Node: Notes1130748 +Node: Compatibility Mode1131613 +Node: Additions1132395 +Node: Accessing The Source1133320 +Node: Adding Code1134756 +Node: New Ports1140934 +Node: Derived Files1145415 +Ref: Derived Files-Footnote-11150496 +Ref: Derived Files-Footnote-21150530 +Ref: Derived Files-Footnote-31151126 +Node: Future Extensions1151240 +Node: Implementation Limitations1151846 +Node: Extension Design1153094 +Node: Old Extension Problems1154248 +Ref: Old Extension Problems-Footnote-11155765 +Node: Extension New Mechanism Goals1155822 +Ref: Extension New Mechanism Goals-Footnote-11159182 +Node: Extension Other Design Decisions1159371 +Node: Extension Future Growth1161477 +Node: Old Extension Mechanism1162313 +Node: Notes summary1164075 +Node: Basic Concepts1165261 +Node: Basic High Level1165942 +Ref: figure-general-flow1166214 +Ref: figure-process-flow1166813 +Ref: Basic High Level-Footnote-11170042 +Node: Basic Data Typing1170227 +Node: Glossary1173555 +Node: Copying1198707 +Node: GNU Free Documentation License1236263 +Node: Index1261399 End Tag Table diff --git a/doc/gawk.texi b/doc/gawk.texi index b418d4cf..74dd35f8 100644 --- a/doc/gawk.texi +++ b/doc/gawk.texi @@ -526,10 +526,10 @@ particular records in a file and perform operations upon them. * Escape Sequences:: How to write nonprinting characters. * Regexp Operators:: Regular Expression Operators. * Bracket Expressions:: What can go between @samp{[...]}. -* GNU Regexp Operators:: Operators specific to GNU software. -* Case-sensitivity:: How to do case-insensitive matching. * Leftmost Longest:: How much text matches. * Computed Regexps:: Using Dynamic Regexps. +* GNU Regexp Operators:: Operators specific to GNU software. +* Case-sensitivity:: How to do case-insensitive matching. * Regexp Summary:: Regular expressions summary. * Records:: Controlling how data is split into records. @@ -1774,6 +1774,7 @@ They also appear in the index under the heading ``dark corner.'' As noted by the opening quote, though, any coverage of dark corners is, by definition, incomplete. +@cindex c.e., See common extensions Extensions to the standard @command{awk} language that are supported by more than one @command{awk} implementation are marked @ifclear FOR_PRINT @@ -2341,24 +2342,19 @@ For example, on OS/2, it is @kbd{Ctrl-z}.) As an example, the following program prints a friendly piece of advice (from Douglas Adams's @cite{The Hitchhiker's Guide to the Galaxy}), to keep you from worrying about the complexities of computer -programming (@code{BEGIN} is a feature we haven't discussed yet): +programming: @example -$ @kbd{awk "BEGIN @{ print \"Don't Panic!\" @}"} +$ @kbd{awk "BEGIN @{ print "Don\47t Panic!" @}"} @print{} Don't Panic! @end example -@cindex shell quoting, double quote -@cindex double quote (@code{"}) in shell commands -@cindex @code{"} (double quote) in shell commands -@cindex @code{\} (backslash) in shell commands -@cindex backslash (@code{\}) in shell commands -This program does not read any input. The @samp{\} before each of the -inner double quotes is necessary because of the shell's quoting -rules---in particular because it mixes both single quotes and -double quotes.@footnote{Although we generally recommend the use of single -quotes around the program text, double quotes are needed here in order to -put the single quote into the message.} +@command{awk} executes statements associated with @code{BEGIN} before +reading any input. If there are no other statements in your program, +as is the case here, @command{awk} just stops, instead of trying to read +input it doesn't know how to process. +The @samp{\47} is a magic way of getting a single quote into +the program, without having to engage in ugly shell quoting tricks. @quotation NOTE As a side note, if you use Bash as your shell, you should execute the @@ -3046,6 +3042,9 @@ awk '@{ if (length($0) > max) max = length($0) @} END @{ print max @}' data @end example +The code associated with @code{END} executes after all +input has been read; it's the other side of the coin to @code{BEGIN}. + @cindex @command{expand} utility @item Print the length of the longest line in @file{data}: @@ -4130,6 +4129,11 @@ included. As each element of @code{ARGV} is processed, @command{gawk} sets the variable @code{ARGIND} to the index in @code{ARGV} of the current element. +@c FIXME: One day, move the ARGC and ARGV node closer to here. +Changing @code{ARGC} and @code{ARGV} in your @command{awk} program lets +you control how @command{awk} processes the input files; this is described +in more detail in @ref{ARGC and ARGV}. + @cindex input files, variable assignments and @cindex variable assignments and input files The distinction between @value{FN} arguments and variable-assignment @@ -4765,10 +4769,10 @@ regular expressions work, we present more complicated instances. * Escape Sequences:: How to write nonprinting characters. * Regexp Operators:: Regular Expression Operators. * Bracket Expressions:: What can go between @samp{[...]}. -* GNU Regexp Operators:: Operators specific to GNU software. -* Case-sensitivity:: How to do case-insensitive matching. * Leftmost Longest:: How much text matches. * Computed Regexps:: Using Dynamic Regexps. +* GNU Regexp Operators:: Operators specific to GNU software. +* Case-sensitivity:: How to do case-insensitive matching. * Regexp Summary:: Regular expressions summary. @end menu @@ -4979,8 +4983,11 @@ However, using more than two hexadecimal digits produces @item \/ A literal slash (necessary for regexp constants only). This sequence is used when you want to write a regexp -constant that contains a slash. Because the regexp is delimited by -slashes, you need to escape the slash that is part of the pattern, +constant that contains a slash +(such as @code{/.*:\/home\/[[:alnum:]]+:.*/}; the @samp{[[:alnum:]]} +notation is discussed shortly, in @ref{Bracket Expressions}). +Because the regexp is delimited by +slashes, you need to escape any slash that is part of the pattern, in order to tell @command{awk} to keep processing the rest of the regexp. @cindex @code{\} (backslash), @code{\"} escape sequence @@ -4988,8 +4995,10 @@ in order to tell @command{awk} to keep processing the rest of the regexp. @item \" A literal double quote (necessary for string constants only). This sequence is used when you want to write a string -constant that contains a double quote. Because the string is delimited by -double quotes, you need to escape the quote that is part of the string, +constant that contains a double quote +(such as @code{"He said \"hi!\" to her."}). +Because the string is delimited by +double quotes, you need to escape any quote that is part of the string, in order to tell @command{awk} to keep processing the rest of the string. @end table @@ -5550,6 +5559,204 @@ they do not recognize collating symbols or equivalence classes. @c maybe one day ... @c ENDOFRANGE charlist +@node Leftmost Longest +@section How Much Text Matches? + +@cindex regular expressions, leftmost longest match +@c @cindex matching, leftmost longest +Consider the following: + +@example +echo aaaabcd | awk '@{ sub(/a+/, "<A>"); print @}' +@end example + +This example uses the @code{sub()} function (which we haven't discussed yet; +@pxref{String Functions}) +to make a change to the input record. Here, the regexp @code{/a+/} +indicates ``one or more @samp{a} characters,'' and the replacement +text is @samp{<A>}. + +The input contains four @samp{a} characters. +@command{awk} (and POSIX) regular expressions always match +the leftmost, @emph{longest} sequence of input characters that can +match. Thus, all four @samp{a} characters are +replaced with @samp{<A>} in this example: + +@example +$ @kbd{echo aaaabcd | awk '@{ sub(/a+/, "<A>"); print @}'} +@print{} <A>bcd +@end example + +For simple match/no-match tests, this is not so important. But when doing +text matching and substitutions with the @code{match()}, @code{sub()}, @code{gsub()}, +and @code{gensub()} functions, it is very important. +@ifinfo +@xref{String Functions}, +for more information on these functions. +@end ifinfo +Understanding this principle is also important for regexp-based record +and field splitting (@pxref{Records}, +and also @pxref{Field Separators}). + +@node Computed Regexps +@section Using Dynamic Regexps + +@c STARTOFRANGE dregexp +@cindex regular expressions, computed +@c STARTOFRANGE regexpd +@cindex regular expressions, dynamic +@cindex @code{~} (tilde), @code{~} operator +@cindex tilde (@code{~}), @code{~} operator +@cindex @code{!} (exclamation point), @code{!~} operator +@cindex exclamation point (@code{!}), @code{!~} operator +@c @cindex operators, @code{~} +@c @cindex operators, @code{!~} +The righthand side of a @samp{~} or @samp{!~} operator need not be a +regexp constant (i.e., a string of characters between slashes). It may +be any expression. The expression is evaluated and converted to a string +if necessary; the contents of the string are then used as the +regexp. A regexp computed in this way is called a @dfn{dynamic +regexp} or a @dfn{computed regexp}: + +@example +BEGIN @{ digits_regexp = "[[:digit:]]+" @} +$0 ~ digits_regexp @{ print @} +@end example + +@noindent +This sets @code{digits_regexp} to a regexp that describes one or more digits, +and tests whether the input record matches this regexp. + +@quotation NOTE +When using the @samp{~} and @samp{!~} +operators, there is a difference between a regexp constant +enclosed in slashes and a string constant enclosed in double quotes. +If you are going to use a string constant, you have to understand that +the string is, in essence, scanned @emph{twice}: the first time when +@command{awk} reads your program, and the second time when it goes to +match the string on the lefthand side of the operator with the pattern +on the right. This is true of any string-valued expression (such as +@code{digits_regexp}, shown previously), not just string constants. +@end quotation + +@cindex regexp constants, slashes vs.@: quotes +@cindex @code{\} (backslash), in regexp constants +@cindex backslash (@code{\}), in regexp constants +@cindex @code{"} (double quote), in regexp constants +@cindex double quote (@code{"}), in regexp constants +What difference does it make if the string is +scanned twice? The answer has to do with escape sequences, and particularly +with backslashes. To get a backslash into a regular expression inside a +string, you have to type two backslashes. + +For example, @code{/\*/} is a regexp constant for a literal @samp{*}. +Only one backslash is needed. To do the same thing with a string, +you have to type @code{"\\*"}. The first backslash escapes the +second one so that the string actually contains the +two characters @samp{\} and @samp{*}. + +@cindex troubleshooting, regexp constants vs.@: string constants +@cindex regexp constants, vs.@: string constants +@cindex string constants, vs.@: regexp constants +Given that you can use both regexp and string constants to describe +regular expressions, which should you use? The answer is ``regexp +constants,'' for several reasons: + +@itemize @value{BULLET} +@item +String constants are more complicated to write and +more difficult to read. Using regexp constants makes your programs +less error-prone. Not understanding the difference between the two +kinds of constants is a common source of errors. + +@item +It is more efficient to use regexp constants. @command{awk} can note +that you have supplied a regexp and store it internally in a form that +makes pattern matching more efficient. When using a string constant, +@command{awk} must first convert the string into this internal form and +then perform the pattern matching. + +@item +Using regexp constants is better form; it shows clearly that you +intend a regexp match. +@end itemize + +@cindex sidebar, Using @code{\n} in Bracket Expressions of Dynamic Regexps +@ifdocbook +@docbook +<sidebar><title>Using @code{\n} in Bracket Expressions of Dynamic Regexps</title> +@end docbook + +@cindex regular expressions, dynamic, with embedded newlines +@cindex newlines, in dynamic regexps + +Some versions of @command{awk} do not allow the newline +character to be used inside a bracket expression for a dynamic regexp: + +@example +$ @kbd{awk '$0 ~ "[ \t\n]"'} +@error{} awk: newline in character class [ +@error{} ]... +@error{} source line number 1 +@error{} context is +@error{} >>> <<< +@end example + +@cindex newlines, in regexp constants +But a newline in a regexp constant works with no problem: + +@example +$ @kbd{awk '$0 ~ /[ \t\n]/'} +@kbd{here is a sample line} +@print{} here is a sample line +@kbd{Ctrl-d} +@end example + +@command{gawk} does not have this problem, and it isn't likely to +occur often in practice, but it's worth noting for future reference. + +@docbook +</sidebar> +@end docbook +@end ifdocbook + +@ifnotdocbook +@cartouche +@center @b{Using @code{\n} in Bracket Expressions of Dynamic Regexps} + + +@cindex regular expressions, dynamic, with embedded newlines +@cindex newlines, in dynamic regexps + +Some versions of @command{awk} do not allow the newline +character to be used inside a bracket expression for a dynamic regexp: + +@example +$ @kbd{awk '$0 ~ "[ \t\n]"'} +@error{} awk: newline in character class [ +@error{} ]... +@error{} source line number 1 +@error{} context is +@error{} >>> <<< +@end example + +@cindex newlines, in regexp constants +But a newline in a regexp constant works with no problem: + +@example +$ @kbd{awk '$0 ~ /[ \t\n]/'} +@kbd{here is a sample line} +@print{} here is a sample line +@kbd{Ctrl-d} +@end example + +@command{gawk} does not have this problem, and it isn't likely to +occur often in practice, but it's worth noting for future reference. +@end cartouche +@end ifnotdocbook +@c ENDOFRANGE dregexp +@c ENDOFRANGE regexpd + @node GNU Regexp Operators @section @command{gawk}-Specific Regexp Operators @@ -5825,204 +6032,6 @@ Case is always significant in compatibility mode. @c ENDOFRANGE csregexp @c ENDOFRANGE regexpcs -@node Leftmost Longest -@section How Much Text Matches? - -@cindex regular expressions, leftmost longest match -@c @cindex matching, leftmost longest -Consider the following: - -@example -echo aaaabcd | awk '@{ sub(/a+/, "<A>"); print @}' -@end example - -This example uses the @code{sub()} function (which we haven't discussed yet; -@pxref{String Functions}) -to make a change to the input record. Here, the regexp @code{/a+/} -indicates ``one or more @samp{a} characters,'' and the replacement -text is @samp{<A>}. - -The input contains four @samp{a} characters. -@command{awk} (and POSIX) regular expressions always match -the leftmost, @emph{longest} sequence of input characters that can -match. Thus, all four @samp{a} characters are -replaced with @samp{<A>} in this example: - -@example -$ @kbd{echo aaaabcd | awk '@{ sub(/a+/, "<A>"); print @}'} -@print{} <A>bcd -@end example - -For simple match/no-match tests, this is not so important. But when doing -text matching and substitutions with the @code{match()}, @code{sub()}, @code{gsub()}, -and @code{gensub()} functions, it is very important. -@ifinfo -@xref{String Functions}, -for more information on these functions. -@end ifinfo -Understanding this principle is also important for regexp-based record -and field splitting (@pxref{Records}, -and also @pxref{Field Separators}). - -@node Computed Regexps -@section Using Dynamic Regexps - -@c STARTOFRANGE dregexp -@cindex regular expressions, computed -@c STARTOFRANGE regexpd -@cindex regular expressions, dynamic -@cindex @code{~} (tilde), @code{~} operator -@cindex tilde (@code{~}), @code{~} operator -@cindex @code{!} (exclamation point), @code{!~} operator -@cindex exclamation point (@code{!}), @code{!~} operator -@c @cindex operators, @code{~} -@c @cindex operators, @code{!~} -The righthand side of a @samp{~} or @samp{!~} operator need not be a -regexp constant (i.e., a string of characters between slashes). It may -be any expression. The expression is evaluated and converted to a string -if necessary; the contents of the string are then used as the -regexp. A regexp computed in this way is called a @dfn{dynamic -regexp} or a @dfn{computed regexp}: - -@example -BEGIN @{ digits_regexp = "[[:digit:]]+" @} -$0 ~ digits_regexp @{ print @} -@end example - -@noindent -This sets @code{digits_regexp} to a regexp that describes one or more digits, -and tests whether the input record matches this regexp. - -@quotation NOTE -When using the @samp{~} and @samp{!~} -operators, there is a difference between a regexp constant -enclosed in slashes and a string constant enclosed in double quotes. -If you are going to use a string constant, you have to understand that -the string is, in essence, scanned @emph{twice}: the first time when -@command{awk} reads your program, and the second time when it goes to -match the string on the lefthand side of the operator with the pattern -on the right. This is true of any string-valued expression (such as -@code{digits_regexp}, shown previously), not just string constants. -@end quotation - -@cindex regexp constants, slashes vs.@: quotes -@cindex @code{\} (backslash), in regexp constants -@cindex backslash (@code{\}), in regexp constants -@cindex @code{"} (double quote), in regexp constants -@cindex double quote (@code{"}), in regexp constants -What difference does it make if the string is -scanned twice? The answer has to do with escape sequences, and particularly -with backslashes. To get a backslash into a regular expression inside a -string, you have to type two backslashes. - -For example, @code{/\*/} is a regexp constant for a literal @samp{*}. -Only one backslash is needed. To do the same thing with a string, -you have to type @code{"\\*"}. The first backslash escapes the -second one so that the string actually contains the -two characters @samp{\} and @samp{*}. - -@cindex troubleshooting, regexp constants vs.@: string constants -@cindex regexp constants, vs.@: string constants -@cindex string constants, vs.@: regexp constants -Given that you can use both regexp and string constants to describe -regular expressions, which should you use? The answer is ``regexp -constants,'' for several reasons: - -@itemize @value{BULLET} -@item -String constants are more complicated to write and -more difficult to read. Using regexp constants makes your programs -less error-prone. Not understanding the difference between the two -kinds of constants is a common source of errors. - -@item -It is more efficient to use regexp constants. @command{awk} can note -that you have supplied a regexp and store it internally in a form that -makes pattern matching more efficient. When using a string constant, -@command{awk} must first convert the string into this internal form and -then perform the pattern matching. - -@item -Using regexp constants is better form; it shows clearly that you -intend a regexp match. -@end itemize - -@cindex sidebar, Using @code{\n} in Bracket Expressions of Dynamic Regexps -@ifdocbook -@docbook -<sidebar><title>Using @code{\n} in Bracket Expressions of Dynamic Regexps</title> -@end docbook - -@cindex regular expressions, dynamic, with embedded newlines -@cindex newlines, in dynamic regexps - -Some versions of @command{awk} do not allow the newline -character to be used inside a bracket expression for a dynamic regexp: - -@example -$ @kbd{awk '$0 ~ "[ \t\n]"'} -@error{} awk: newline in character class [ -@error{} ]... -@error{} source line number 1 -@error{} context is -@error{} >>> <<< -@end example - -@cindex newlines, in regexp constants -But a newline in a regexp constant works with no problem: - -@example -$ @kbd{awk '$0 ~ /[ \t\n]/'} -@kbd{here is a sample line} -@print{} here is a sample line -@kbd{Ctrl-d} -@end example - -@command{gawk} does not have this problem, and it isn't likely to -occur often in practice, but it's worth noting for future reference. - -@docbook -</sidebar> -@end docbook -@end ifdocbook - -@ifnotdocbook -@cartouche -@center @b{Using @code{\n} in Bracket Expressions of Dynamic Regexps} - - -@cindex regular expressions, dynamic, with embedded newlines -@cindex newlines, in dynamic regexps - -Some versions of @command{awk} do not allow the newline -character to be used inside a bracket expression for a dynamic regexp: - -@example -$ @kbd{awk '$0 ~ "[ \t\n]"'} -@error{} awk: newline in character class [ -@error{} ]... -@error{} source line number 1 -@error{} context is -@error{} >>> <<< -@end example - -@cindex newlines, in regexp constants -But a newline in a regexp constant works with no problem: - -@example -$ @kbd{awk '$0 ~ /[ \t\n]/'} -@kbd{here is a sample line} -@print{} here is a sample line -@kbd{Ctrl-d} -@end example - -@command{gawk} does not have this problem, and it isn't likely to -occur often in practice, but it's worth noting for future reference. -@end cartouche -@end ifnotdocbook -@c ENDOFRANGE dregexp -@c ENDOFRANGE regexpd - @node Regexp Summary @section Summary @@ -7965,32 +7974,48 @@ finished processing the current record, but want to do some special processing on the next record @emph{right now}. For example: @example +# Remove text between /* and */, inclusive @{ - if ((t = index($0, "/*")) != 0) @{ - # value of `tmp' will be "" if t is 1 - tmp = substr($0, 1, t - 1) - u = index(substr($0, t + 2), "*/") - offset = t + 2 - while (u == 0) @{ - if (getline <= 0) @{ + if ((i = index($0, "/*")) != 0) @{ + out = substr($0, 1, i - 1) # leading part of the string + rest = substr($0, i + 2) # ... */ ... + j = index(rest, "*/") # is */ in trailing part? + if (j > 0) @{ + rest = substr(rest, j + 2) # remove comment + @} else @{ + while (j == 0) @{ + # get more text + if (getline <= 0) @{ m = "unexpected EOF or error" m = (m ": " ERRNO) print m > "/dev/stderr" exit - @} - u = index($0, "*/") - offset = 0 - @} - # substr() expression will be "" if */ - # occurred at end of line - $0 = tmp substr($0, offset + u + 2) - @} - print $0 + @} + # build up the line using string concatenation + rest = rest $0 + j = index(rest, "*/") # is */ in trailing part? + if (j != 0) @{ + rest = substr(rest, j + 2) + break + @} + @} + @} + # build up the output line using string concatenation + $0 = out rest + @} + print $0 @} @end example This @command{awk} program deletes C-style comments (@samp{/* @dots{} -*/}) from the input. By replacing the @samp{print $0} with other +*/}) from the input. +It uses a number of features we haven't covered yet, including +string concatenation +(@pxref{Concatenation}) +and the @code{index()} and @code{substr()} built-in +functions +(@pxref{String Functions}). +By replacing the @samp{print $0} with other statements, you could perform more complicated processing on the decommented input, such as searching for matches of a regular expression. (This program has a subtle problem---it does not work if one @@ -8681,7 +8706,7 @@ including abstentions, for each item. comments (@samp{/* @dots{} */}) from the input. That program does not work if one comment ends on one line and another one starts later on the same line. -Write a program that does handle multiple comments on the line. +That can be fixed by making one simple change. What is it? @end enumerate @c EXCLUDE END @@ -10511,7 +10536,8 @@ A regexp constant is a regular expression description enclosed in slashes, such as @code{@w{/^beginning and end$/}}. Most regexps used in @command{awk} programs are constant, but the @samp{~} and @samp{!~} matching operators can also match computed or dynamic regexps -(which are just ordinary strings or variables that contain a regexp). +(which are typically just ordinary strings or variables that contain a regexp, +but could be a more complex expression). @c ENDOFRANGE cnst @node Using Constant Regexps @@ -12302,7 +12328,7 @@ program is one way to print lines in between special bracketing lines: @example $1 == "START" @{ interested = ! interested; next @} -interested == 1 @{ print @} +interested @{ print @} $1 == "END" @{ interested = ! interested; next @} @end example @@ -12322,6 +12348,16 @@ bogus input data, but the point is to illustrate the use of `!', so we'll leave well enough alone. @end ignore +Most commonly, the @samp{!} operator is used in the conditions of +@code{if} and @code{while} statements, where it often makes more +sense to phrase the logic in the negative: + +@example +if (! @var{some condition} || @var{some other condition}) @{ + @var{@dots{} do whatever processing @dots{}} +@} +@end example + @cindex @code{next} statement @quotation NOTE The @code{next} statement is discussed in @@ -14114,7 +14150,8 @@ starts over with the first rule in the program. If the @code{nextfile} statement causes the end of the input to be reached, then the code in any @code{END} rules is executed. An exception to this is when @code{nextfile} is invoked during execution of any statement in an -@code{END} rule; In this case, it causes the program to stop immediately. @xref{BEGIN/END}. +@code{END} rule; in this case, it causes the program to stop immediately. +@xref{BEGIN/END}. The @code{nextfile} statement is useful when there are many @value{DF}s to process but it isn't necessary to process every record in every file. @@ -14124,13 +14161,10 @@ would have to continue scanning the unwanted records. The @code{nextfile} statement accomplishes this much more efficiently. In @command{gawk}, execution of @code{nextfile} causes additional things -to happen: -any @code{ENDFILE} rules are executed except in the case as -mentioned below, -@code{ARGIND} is incremented, -and -any @code{BEGINFILE} rules are executed. -(@code{ARGIND} hasn't been introduced yet. @xref{Built-in Variables}.) +to happen: any @code{ENDFILE} rules are executed if @command{gawk} is +not currently in an @code{END} or @code{BEGINFILE} rule, @code{ARGIND} is +incremented, and any @code{BEGINFILE} rules are executed. (@code{ARGIND} +hasn't been introduced yet. @xref{Built-in Variables}.) With @command{gawk}, @code{nextfile} is useful inside a @code{BEGINFILE} rule to skip over a file that would otherwise cause @command{gawk} @@ -16152,7 +16186,7 @@ $ @kbd{echo 'line 1} > @kbd{line 2} > @kbd{line 3' | awk '@{ l[lines] = $0; ++lines @}} > @kbd{END @{} -> @kbd{for (i = lines-1; i >= 0; --i)} +> @kbd{for (i = lines - 1; i >= 0; i--)} > @kbd{print l[i]} > @kbd{@}'} @print{} line 3 @@ -16176,7 +16210,7 @@ The following version of the program works correctly: @example @{ l[lines++] = $0 @} END @{ - for (i = lines - 1; i >= 0; --i) + for (i = lines - 1; i >= 0; i--) print l[i] @} @end example @@ -20455,8 +20489,9 @@ function mystrtonum(str, ret, n, i, k, c) ret = 0 for (i = 1; i <= n; i++) @{ c = substr(str, i, 1) - if ((k = index("01234567", c)) > 0) - k-- # adjust for 1-basing in awk + # index() returns 0 if c not in string, + # includes c == "0" + k = index("1234567", c) ret = ret * 8 + k @} @@ -20468,6 +20503,8 @@ function mystrtonum(str, ret, n, i, k, c) for (i = 1; i <= n; i++) @{ c = substr(str, i, 1) c = tolower(c) + # index() returns 0 if c not in string, + # includes c == "0" k = index("123456789abcdef", c) ret = ret * 16 + k @@ -21070,7 +21107,12 @@ function readfile(file, tmp, contents) This function reads from @code{file} one record at a time, building up the full contents of the file in the local variable @code{contents}. -It works, but is not necessarily efficient. +It works, but is not necessarily +@c 8/2014. Thanks to BWK for pointing this out: +efficient.@footnote{Execution time grows quadratically in the size of +the input; for each record, @command{awk} has to allocate a bigger +internal buffer for @code{contents}, copy the old contents into it, +and then append the contents of the new record.} The following function, based on a suggestion by Denis Shirokov, reads the entire contents of the named file in one shot: @@ -21743,8 +21785,7 @@ it is not an option, and it ends option processing. Continuing on: i = index(options, thisopt) if (i == 0) @{ if (Opterr) - printf("%c -- invalid option\n", - thisopt) > "/dev/stderr" + printf("%c -- invalid option\n", thisopt) > "/dev/stderr" if (_opti >= length(argv[Optind])) @{ Optind++ _opti = 0 diff --git a/doc/gawktexi.in b/doc/gawktexi.in index da427d9b..8091e16c 100644 --- a/doc/gawktexi.in +++ b/doc/gawktexi.in @@ -521,10 +521,10 @@ particular records in a file and perform operations upon them. * Escape Sequences:: How to write nonprinting characters. * Regexp Operators:: Regular Expression Operators. * Bracket Expressions:: What can go between @samp{[...]}. -* GNU Regexp Operators:: Operators specific to GNU software. -* Case-sensitivity:: How to do case-insensitive matching. * Leftmost Longest:: How much text matches. * Computed Regexps:: Using Dynamic Regexps. +* GNU Regexp Operators:: Operators specific to GNU software. +* Case-sensitivity:: How to do case-insensitive matching. * Regexp Summary:: Regular expressions summary. * Records:: Controlling how data is split into records. @@ -1741,6 +1741,7 @@ They also appear in the index under the heading ``dark corner.'' As noted by the opening quote, though, any coverage of dark corners is, by definition, incomplete. +@cindex c.e., See common extensions Extensions to the standard @command{awk} language that are supported by more than one @command{awk} implementation are marked @ifclear FOR_PRINT @@ -2308,24 +2309,19 @@ For example, on OS/2, it is @kbd{Ctrl-z}.) As an example, the following program prints a friendly piece of advice (from Douglas Adams's @cite{The Hitchhiker's Guide to the Galaxy}), to keep you from worrying about the complexities of computer -programming (@code{BEGIN} is a feature we haven't discussed yet): +programming: @example -$ @kbd{awk "BEGIN @{ print \"Don't Panic!\" @}"} +$ @kbd{awk "BEGIN @{ print "Don\47t Panic!" @}"} @print{} Don't Panic! @end example -@cindex shell quoting, double quote -@cindex double quote (@code{"}) in shell commands -@cindex @code{"} (double quote) in shell commands -@cindex @code{\} (backslash) in shell commands -@cindex backslash (@code{\}) in shell commands -This program does not read any input. The @samp{\} before each of the -inner double quotes is necessary because of the shell's quoting -rules---in particular because it mixes both single quotes and -double quotes.@footnote{Although we generally recommend the use of single -quotes around the program text, double quotes are needed here in order to -put the single quote into the message.} +@command{awk} executes statements associated with @code{BEGIN} before +reading any input. If there are no other statements in your program, +as is the case here, @command{awk} just stops, instead of trying to read +input it doesn't know how to process. +The @samp{\47} is a magic way of getting a single quote into +the program, without having to engage in ugly shell quoting tricks. @quotation NOTE As a side note, if you use Bash as your shell, you should execute the @@ -2957,6 +2953,9 @@ awk '@{ if (length($0) > max) max = length($0) @} END @{ print max @}' data @end example +The code associated with @code{END} executes after all +input has been read; it's the other side of the coin to @code{BEGIN}. + @cindex @command{expand} utility @item Print the length of the longest line in @file{data}: @@ -4041,6 +4040,11 @@ included. As each element of @code{ARGV} is processed, @command{gawk} sets the variable @code{ARGIND} to the index in @code{ARGV} of the current element. +@c FIXME: One day, move the ARGC and ARGV node closer to here. +Changing @code{ARGC} and @code{ARGV} in your @command{awk} program lets +you control how @command{awk} processes the input files; this is described +in more detail in @ref{ARGC and ARGV}. + @cindex input files, variable assignments and @cindex variable assignments and input files The distinction between @value{FN} arguments and variable-assignment @@ -4676,10 +4680,10 @@ regular expressions work, we present more complicated instances. * Escape Sequences:: How to write nonprinting characters. * Regexp Operators:: Regular Expression Operators. * Bracket Expressions:: What can go between @samp{[...]}. -* GNU Regexp Operators:: Operators specific to GNU software. -* Case-sensitivity:: How to do case-insensitive matching. * Leftmost Longest:: How much text matches. * Computed Regexps:: Using Dynamic Regexps. +* GNU Regexp Operators:: Operators specific to GNU software. +* Case-sensitivity:: How to do case-insensitive matching. * Regexp Summary:: Regular expressions summary. @end menu @@ -4890,8 +4894,11 @@ However, using more than two hexadecimal digits produces @item \/ A literal slash (necessary for regexp constants only). This sequence is used when you want to write a regexp -constant that contains a slash. Because the regexp is delimited by -slashes, you need to escape the slash that is part of the pattern, +constant that contains a slash +(such as @code{/.*:\/home\/[[:alnum:]]+:.*/}; the @samp{[[:alnum:]]} +notation is discussed shortly, in @ref{Bracket Expressions}). +Because the regexp is delimited by +slashes, you need to escape any slash that is part of the pattern, in order to tell @command{awk} to keep processing the rest of the regexp. @cindex @code{\} (backslash), @code{\"} escape sequence @@ -4899,8 +4906,10 @@ in order to tell @command{awk} to keep processing the rest of the regexp. @item \" A literal double quote (necessary for string constants only). This sequence is used when you want to write a string -constant that contains a double quote. Because the string is delimited by -double quotes, you need to escape the quote that is part of the string, +constant that contains a double quote +(such as @code{"He said \"hi!\" to her."}). +Because the string is delimited by +double quotes, you need to escape any quote that is part of the string, in order to tell @command{awk} to keep processing the rest of the string. @end table @@ -5378,6 +5387,160 @@ they do not recognize collating symbols or equivalence classes. @c maybe one day ... @c ENDOFRANGE charlist +@node Leftmost Longest +@section How Much Text Matches? + +@cindex regular expressions, leftmost longest match +@c @cindex matching, leftmost longest +Consider the following: + +@example +echo aaaabcd | awk '@{ sub(/a+/, "<A>"); print @}' +@end example + +This example uses the @code{sub()} function (which we haven't discussed yet; +@pxref{String Functions}) +to make a change to the input record. Here, the regexp @code{/a+/} +indicates ``one or more @samp{a} characters,'' and the replacement +text is @samp{<A>}. + +The input contains four @samp{a} characters. +@command{awk} (and POSIX) regular expressions always match +the leftmost, @emph{longest} sequence of input characters that can +match. Thus, all four @samp{a} characters are +replaced with @samp{<A>} in this example: + +@example +$ @kbd{echo aaaabcd | awk '@{ sub(/a+/, "<A>"); print @}'} +@print{} <A>bcd +@end example + +For simple match/no-match tests, this is not so important. But when doing +text matching and substitutions with the @code{match()}, @code{sub()}, @code{gsub()}, +and @code{gensub()} functions, it is very important. +@ifinfo +@xref{String Functions}, +for more information on these functions. +@end ifinfo +Understanding this principle is also important for regexp-based record +and field splitting (@pxref{Records}, +and also @pxref{Field Separators}). + +@node Computed Regexps +@section Using Dynamic Regexps + +@c STARTOFRANGE dregexp +@cindex regular expressions, computed +@c STARTOFRANGE regexpd +@cindex regular expressions, dynamic +@cindex @code{~} (tilde), @code{~} operator +@cindex tilde (@code{~}), @code{~} operator +@cindex @code{!} (exclamation point), @code{!~} operator +@cindex exclamation point (@code{!}), @code{!~} operator +@c @cindex operators, @code{~} +@c @cindex operators, @code{!~} +The righthand side of a @samp{~} or @samp{!~} operator need not be a +regexp constant (i.e., a string of characters between slashes). It may +be any expression. The expression is evaluated and converted to a string +if necessary; the contents of the string are then used as the +regexp. A regexp computed in this way is called a @dfn{dynamic +regexp} or a @dfn{computed regexp}: + +@example +BEGIN @{ digits_regexp = "[[:digit:]]+" @} +$0 ~ digits_regexp @{ print @} +@end example + +@noindent +This sets @code{digits_regexp} to a regexp that describes one or more digits, +and tests whether the input record matches this regexp. + +@quotation NOTE +When using the @samp{~} and @samp{!~} +operators, there is a difference between a regexp constant +enclosed in slashes and a string constant enclosed in double quotes. +If you are going to use a string constant, you have to understand that +the string is, in essence, scanned @emph{twice}: the first time when +@command{awk} reads your program, and the second time when it goes to +match the string on the lefthand side of the operator with the pattern +on the right. This is true of any string-valued expression (such as +@code{digits_regexp}, shown previously), not just string constants. +@end quotation + +@cindex regexp constants, slashes vs.@: quotes +@cindex @code{\} (backslash), in regexp constants +@cindex backslash (@code{\}), in regexp constants +@cindex @code{"} (double quote), in regexp constants +@cindex double quote (@code{"}), in regexp constants +What difference does it make if the string is +scanned twice? The answer has to do with escape sequences, and particularly +with backslashes. To get a backslash into a regular expression inside a +string, you have to type two backslashes. + +For example, @code{/\*/} is a regexp constant for a literal @samp{*}. +Only one backslash is needed. To do the same thing with a string, +you have to type @code{"\\*"}. The first backslash escapes the +second one so that the string actually contains the +two characters @samp{\} and @samp{*}. + +@cindex troubleshooting, regexp constants vs.@: string constants +@cindex regexp constants, vs.@: string constants +@cindex string constants, vs.@: regexp constants +Given that you can use both regexp and string constants to describe +regular expressions, which should you use? The answer is ``regexp +constants,'' for several reasons: + +@itemize @value{BULLET} +@item +String constants are more complicated to write and +more difficult to read. Using regexp constants makes your programs +less error-prone. Not understanding the difference between the two +kinds of constants is a common source of errors. + +@item +It is more efficient to use regexp constants. @command{awk} can note +that you have supplied a regexp and store it internally in a form that +makes pattern matching more efficient. When using a string constant, +@command{awk} must first convert the string into this internal form and +then perform the pattern matching. + +@item +Using regexp constants is better form; it shows clearly that you +intend a regexp match. +@end itemize + +@sidebar Using @code{\n} in Bracket Expressions of Dynamic Regexps +@cindex regular expressions, dynamic, with embedded newlines +@cindex newlines, in dynamic regexps + +Some versions of @command{awk} do not allow the newline +character to be used inside a bracket expression for a dynamic regexp: + +@example +$ @kbd{awk '$0 ~ "[ \t\n]"'} +@error{} awk: newline in character class [ +@error{} ]... +@error{} source line number 1 +@error{} context is +@error{} >>> <<< +@end example + +@cindex newlines, in regexp constants +But a newline in a regexp constant works with no problem: + +@example +$ @kbd{awk '$0 ~ /[ \t\n]/'} +@kbd{here is a sample line} +@print{} here is a sample line +@kbd{Ctrl-d} +@end example + +@command{gawk} does not have this problem, and it isn't likely to +occur often in practice, but it's worth noting for future reference. +@end sidebar +@c ENDOFRANGE dregexp +@c ENDOFRANGE regexpd + @node GNU Regexp Operators @section @command{gawk}-Specific Regexp Operators @@ -5653,160 +5816,6 @@ Case is always significant in compatibility mode. @c ENDOFRANGE csregexp @c ENDOFRANGE regexpcs -@node Leftmost Longest -@section How Much Text Matches? - -@cindex regular expressions, leftmost longest match -@c @cindex matching, leftmost longest -Consider the following: - -@example -echo aaaabcd | awk '@{ sub(/a+/, "<A>"); print @}' -@end example - -This example uses the @code{sub()} function (which we haven't discussed yet; -@pxref{String Functions}) -to make a change to the input record. Here, the regexp @code{/a+/} -indicates ``one or more @samp{a} characters,'' and the replacement -text is @samp{<A>}. - -The input contains four @samp{a} characters. -@command{awk} (and POSIX) regular expressions always match -the leftmost, @emph{longest} sequence of input characters that can -match. Thus, all four @samp{a} characters are -replaced with @samp{<A>} in this example: - -@example -$ @kbd{echo aaaabcd | awk '@{ sub(/a+/, "<A>"); print @}'} -@print{} <A>bcd -@end example - -For simple match/no-match tests, this is not so important. But when doing -text matching and substitutions with the @code{match()}, @code{sub()}, @code{gsub()}, -and @code{gensub()} functions, it is very important. -@ifinfo -@xref{String Functions}, -for more information on these functions. -@end ifinfo -Understanding this principle is also important for regexp-based record -and field splitting (@pxref{Records}, -and also @pxref{Field Separators}). - -@node Computed Regexps -@section Using Dynamic Regexps - -@c STARTOFRANGE dregexp -@cindex regular expressions, computed -@c STARTOFRANGE regexpd -@cindex regular expressions, dynamic -@cindex @code{~} (tilde), @code{~} operator -@cindex tilde (@code{~}), @code{~} operator -@cindex @code{!} (exclamation point), @code{!~} operator -@cindex exclamation point (@code{!}), @code{!~} operator -@c @cindex operators, @code{~} -@c @cindex operators, @code{!~} -The righthand side of a @samp{~} or @samp{!~} operator need not be a -regexp constant (i.e., a string of characters between slashes). It may -be any expression. The expression is evaluated and converted to a string -if necessary; the contents of the string are then used as the -regexp. A regexp computed in this way is called a @dfn{dynamic -regexp} or a @dfn{computed regexp}: - -@example -BEGIN @{ digits_regexp = "[[:digit:]]+" @} -$0 ~ digits_regexp @{ print @} -@end example - -@noindent -This sets @code{digits_regexp} to a regexp that describes one or more digits, -and tests whether the input record matches this regexp. - -@quotation NOTE -When using the @samp{~} and @samp{!~} -operators, there is a difference between a regexp constant -enclosed in slashes and a string constant enclosed in double quotes. -If you are going to use a string constant, you have to understand that -the string is, in essence, scanned @emph{twice}: the first time when -@command{awk} reads your program, and the second time when it goes to -match the string on the lefthand side of the operator with the pattern -on the right. This is true of any string-valued expression (such as -@code{digits_regexp}, shown previously), not just string constants. -@end quotation - -@cindex regexp constants, slashes vs.@: quotes -@cindex @code{\} (backslash), in regexp constants -@cindex backslash (@code{\}), in regexp constants -@cindex @code{"} (double quote), in regexp constants -@cindex double quote (@code{"}), in regexp constants -What difference does it make if the string is -scanned twice? The answer has to do with escape sequences, and particularly -with backslashes. To get a backslash into a regular expression inside a -string, you have to type two backslashes. - -For example, @code{/\*/} is a regexp constant for a literal @samp{*}. -Only one backslash is needed. To do the same thing with a string, -you have to type @code{"\\*"}. The first backslash escapes the -second one so that the string actually contains the -two characters @samp{\} and @samp{*}. - -@cindex troubleshooting, regexp constants vs.@: string constants -@cindex regexp constants, vs.@: string constants -@cindex string constants, vs.@: regexp constants -Given that you can use both regexp and string constants to describe -regular expressions, which should you use? The answer is ``regexp -constants,'' for several reasons: - -@itemize @value{BULLET} -@item -String constants are more complicated to write and -more difficult to read. Using regexp constants makes your programs -less error-prone. Not understanding the difference between the two -kinds of constants is a common source of errors. - -@item -It is more efficient to use regexp constants. @command{awk} can note -that you have supplied a regexp and store it internally in a form that -makes pattern matching more efficient. When using a string constant, -@command{awk} must first convert the string into this internal form and -then perform the pattern matching. - -@item -Using regexp constants is better form; it shows clearly that you -intend a regexp match. -@end itemize - -@sidebar Using @code{\n} in Bracket Expressions of Dynamic Regexps -@cindex regular expressions, dynamic, with embedded newlines -@cindex newlines, in dynamic regexps - -Some versions of @command{awk} do not allow the newline -character to be used inside a bracket expression for a dynamic regexp: - -@example -$ @kbd{awk '$0 ~ "[ \t\n]"'} -@error{} awk: newline in character class [ -@error{} ]... -@error{} source line number 1 -@error{} context is -@error{} >>> <<< -@end example - -@cindex newlines, in regexp constants -But a newline in a regexp constant works with no problem: - -@example -$ @kbd{awk '$0 ~ /[ \t\n]/'} -@kbd{here is a sample line} -@print{} here is a sample line -@kbd{Ctrl-d} -@end example - -@command{gawk} does not have this problem, and it isn't likely to -occur often in practice, but it's worth noting for future reference. -@end sidebar -@c ENDOFRANGE dregexp -@c ENDOFRANGE regexpd - @node Regexp Summary @section Summary @@ -7567,32 +7576,48 @@ finished processing the current record, but want to do some special processing on the next record @emph{right now}. For example: @example +# Remove text between /* and */, inclusive @{ - if ((t = index($0, "/*")) != 0) @{ - # value of `tmp' will be "" if t is 1 - tmp = substr($0, 1, t - 1) - u = index(substr($0, t + 2), "*/") - offset = t + 2 - while (u == 0) @{ - if (getline <= 0) @{ + if ((i = index($0, "/*")) != 0) @{ + out = substr($0, 1, i - 1) # leading part of the string + rest = substr($0, i + 2) # ... */ ... + j = index(rest, "*/") # is */ in trailing part? + if (j > 0) @{ + rest = substr(rest, j + 2) # remove comment + @} else @{ + while (j == 0) @{ + # get more text + if (getline <= 0) @{ m = "unexpected EOF or error" m = (m ": " ERRNO) print m > "/dev/stderr" exit - @} - u = index($0, "*/") - offset = 0 - @} - # substr() expression will be "" if */ - # occurred at end of line - $0 = tmp substr($0, offset + u + 2) - @} - print $0 + @} + # build up the line using string concatenation + rest = rest $0 + j = index(rest, "*/") # is */ in trailing part? + if (j != 0) @{ + rest = substr(rest, j + 2) + break + @} + @} + @} + # build up the output line using string concatenation + $0 = out rest + @} + print $0 @} @end example This @command{awk} program deletes C-style comments (@samp{/* @dots{} -*/}) from the input. By replacing the @samp{print $0} with other +*/}) from the input. +It uses a number of features we haven't covered yet, including +string concatenation +(@pxref{Concatenation}) +and the @code{index()} and @code{substr()} built-in +functions +(@pxref{String Functions}). +By replacing the @samp{print $0} with other statements, you could perform more complicated processing on the decommented input, such as searching for matches of a regular expression. (This program has a subtle problem---it does not work if one @@ -8283,7 +8308,7 @@ including abstentions, for each item. comments (@samp{/* @dots{} */}) from the input. That program does not work if one comment ends on one line and another one starts later on the same line. -Write a program that does handle multiple comments on the line. +That can be fixed by making one simple change. What is it? @end enumerate @c EXCLUDE END @@ -9984,7 +10009,8 @@ A regexp constant is a regular expression description enclosed in slashes, such as @code{@w{/^beginning and end$/}}. Most regexps used in @command{awk} programs are constant, but the @samp{~} and @samp{!~} matching operators can also match computed or dynamic regexps -(which are just ordinary strings or variables that contain a regexp). +(which are typically just ordinary strings or variables that contain a regexp, +but could be a more complex expression). @c ENDOFRANGE cnst @node Using Constant Regexps @@ -11636,7 +11662,7 @@ program is one way to print lines in between special bracketing lines: @example $1 == "START" @{ interested = ! interested; next @} -interested == 1 @{ print @} +interested @{ print @} $1 == "END" @{ interested = ! interested; next @} @end example @@ -11656,6 +11682,16 @@ bogus input data, but the point is to illustrate the use of `!', so we'll leave well enough alone. @end ignore +Most commonly, the @samp{!} operator is used in the conditions of +@code{if} and @code{while} statements, where it often makes more +sense to phrase the logic in the negative: + +@example +if (! @var{some condition} || @var{some other condition}) @{ + @var{@dots{} do whatever processing @dots{}} +@} +@end example + @cindex @code{next} statement @quotation NOTE The @code{next} statement is discussed in @@ -13448,7 +13484,8 @@ starts over with the first rule in the program. If the @code{nextfile} statement causes the end of the input to be reached, then the code in any @code{END} rules is executed. An exception to this is when @code{nextfile} is invoked during execution of any statement in an -@code{END} rule; In this case, it causes the program to stop immediately. @xref{BEGIN/END}. +@code{END} rule; in this case, it causes the program to stop immediately. +@xref{BEGIN/END}. The @code{nextfile} statement is useful when there are many @value{DF}s to process but it isn't necessary to process every record in every file. @@ -13458,13 +13495,10 @@ would have to continue scanning the unwanted records. The @code{nextfile} statement accomplishes this much more efficiently. In @command{gawk}, execution of @code{nextfile} causes additional things -to happen: -any @code{ENDFILE} rules are executed except in the case as -mentioned below, -@code{ARGIND} is incremented, -and -any @code{BEGINFILE} rules are executed. -(@code{ARGIND} hasn't been introduced yet. @xref{Built-in Variables}.) +to happen: any @code{ENDFILE} rules are executed if @command{gawk} is +not currently in an @code{END} or @code{BEGINFILE} rule, @code{ARGIND} is +incremented, and any @code{BEGINFILE} rules are executed. (@code{ARGIND} +hasn't been introduced yet. @xref{Built-in Variables}.) With @command{gawk}, @code{nextfile} is useful inside a @code{BEGINFILE} rule to skip over a file that would otherwise cause @command{gawk} @@ -15440,7 +15474,7 @@ $ @kbd{echo 'line 1} > @kbd{line 2} > @kbd{line 3' | awk '@{ l[lines] = $0; ++lines @}} > @kbd{END @{} -> @kbd{for (i = lines-1; i >= 0; --i)} +> @kbd{for (i = lines - 1; i >= 0; i--)} > @kbd{print l[i]} > @kbd{@}'} @print{} line 3 @@ -15464,7 +15498,7 @@ The following version of the program works correctly: @example @{ l[lines++] = $0 @} END @{ - for (i = lines - 1; i >= 0; --i) + for (i = lines - 1; i >= 0; i--) print l[i] @} @end example @@ -19582,8 +19616,9 @@ function mystrtonum(str, ret, n, i, k, c) ret = 0 for (i = 1; i <= n; i++) @{ c = substr(str, i, 1) - if ((k = index("01234567", c)) > 0) - k-- # adjust for 1-basing in awk + # index() returns 0 if c not in string, + # includes c == "0" + k = index("1234567", c) ret = ret * 8 + k @} @@ -19595,6 +19630,8 @@ function mystrtonum(str, ret, n, i, k, c) for (i = 1; i <= n; i++) @{ c = substr(str, i, 1) c = tolower(c) + # index() returns 0 if c not in string, + # includes c == "0" k = index("123456789abcdef", c) ret = ret * 16 + k @@ -20197,7 +20234,12 @@ function readfile(file, tmp, contents) This function reads from @code{file} one record at a time, building up the full contents of the file in the local variable @code{contents}. -It works, but is not necessarily efficient. +It works, but is not necessarily +@c 8/2014. Thanks to BWK for pointing this out: +efficient.@footnote{Execution time grows quadratically in the size of +the input; for each record, @command{awk} has to allocate a bigger +internal buffer for @code{contents}, copy the old contents into it, +and then append the contents of the new record.} The following function, based on a suggestion by Denis Shirokov, reads the entire contents of the named file in one shot: @@ -20841,8 +20883,7 @@ it is not an option, and it ends option processing. Continuing on: i = index(options, thisopt) if (i == 0) @{ if (Opterr) - printf("%c -- invalid option\n", - thisopt) > "/dev/stderr" + printf("%c -- invalid option\n", thisopt) > "/dev/stderr" if (_opti >= length(argv[Optind])) @{ Optind++ _opti = 0 |