diff options
Diffstat (limited to 'x2p/a2p.man')
| -rw-r--r-- | x2p/a2p.man | 191 |
1 files changed, 191 insertions, 0 deletions
diff --git a/x2p/a2p.man b/x2p/a2p.man new file mode 100644 index 0000000000..d367526893 --- /dev/null +++ b/x2p/a2p.man @@ -0,0 +1,191 @@ +.rn '' }` +''' $Header: a2p.man,v 1.0 87/12/18 17:23:56 root Exp $ +''' +''' $Log: a2p.man,v $ +''' Revision 1.0 87/12/18 17:23:56 root +''' Initial revision +''' +''' +.de Sh +.br +.ne 5 +.PP +\fB\\$1\fR +.PP +.. +.de Sp +.if t .sp .5v +.if n .sp +.. +.de Ip +.br +.ie \\n.$>=3 .ne \\$3 +.el .ne 3 +.IP "\\$1" \\$2 +.. +''' +''' Set up \*(-- to give an unbreakable dash; +''' string Tr holds user defined translation string. +''' Bell System Logo is used as a dummy character. +''' +.tr \(bs-|\(bv\*(Tr +.ie n \{\ +.ds -- \(bs- +.if (\n(.H=4u)&(1m=24u) .ds -- \(bs\h'-12u'\(bs\h'-12u'-\" diablo 10 pitch +.if (\n(.H=4u)&(1m=20u) .ds -- \(bs\h'-12u'\(bs\h'-8u'-\" diablo 12 pitch +.ds L" "" +.ds R" "" +.ds L' ' +.ds R' ' +'br\} +.el\{\ +.ds -- \(em\| +.tr \*(Tr +.ds L" `` +.ds R" '' +.ds L' ` +.ds R' ' +'br\} +.TH A2P 1 LOCAL +.SH NAME +a2p - Awk to Perl translator +.SH SYNOPSIS +.B a2p [options] filename +.SH DESCRIPTION +.I A2p +takes an awk script specified on the command line (or from standard input) +and produces a comparable +.I perl +script on the standard output. +.Sh "Options" +Options include: +.TP 5 +.B \-D<number> +sets debugging flags. +.TP 5 +.B \-F<character> +tells a2p that this awk script is always invoked with this -F switch. +.TP 5 +.B \-n<fieldlist> +specifies the names of the input fields if input does not have to be split into +an array. +If you were translating an awk script that processes the password file, you +might say: +.sp + a2p -7 -nlogin.password.uid.gid.gcos.shell.home +.sp +Any delimiter will do to separate the field names. +.TP 5 +.B \-<number> +causes a2p to assume that input will always have that many fields. +.Sh "Considerations" +A2p cannot do as good a job translating as a human would, but it usually +does pretty well. +There are some areas where you may want to examine the perl script produced +and tweak it some. +Here are some of them, in no particular order. +.PP +The split operator in perl always strips off all null fields from the end. +Awk does NOT do this, if you've set FS. +If the perl script splits to an array, the field count may not reflect +what you expect. +Ordinarily this isn't a problem, since nonexistent array elements have a null +value, but if you rely on NF in awk, you could be in for trouble. +Either force the number of fields with \-<number>, or count the number of +delimiters another way, e.g. with y/:/:/. +Or add something non-null to the end before you split, and then pop it off +the resulting array. +.PP +There is an awk idiom of putting int() around a string expression to force +numeric interpretation, even though the argument is always integer anyway. +This is generally unneeded in perl, but a2p can't tell if the argument +is always going to be integer, so it leaves it in. +You may wish to remove it. +.PP +Perl differentiates numeric comparison from string comparison. +Awk has one operator for both that decides at run time which comparison +to do. +A2p does not try to do a complete job of awk emulation at this point. +Instead it guesses which one you want. +It's almost always right, but it can be spoofed. +All such guesses are marked with the comment \*(L"#???\*(R". +You should go through and check them. +.PP +Perl does not attempt to emulate the behavior of awk in which nonexistent +array elements spring into existence simply by being referenced. +If somehow you are relying on this mechanism to create null entries for +a subsequent for...in, they won't be there in perl. +.PP +If a2p makes a split line that assigns to a list of variables that looks +like (Fld1, Fld2, Fld3...) you may want +to rerun a2p using the \-n option mentioned above. +This will let you name the fields throughout the script. +If it splits to an array instead, the script is probably referring to the number +of fields somewhere. +.PP +The exit statement in awk doesn't necessarily exit; it goes to the END +block if there is one. +Awk scripts that do contortions within the END block to bypass the block under +such circumstances can be simplified by removing the conditional +in the END block and just exiting directly from the perl script. +.PP +Perl has two kinds of array, numerically-indexed and associative. +Awk arrays are usually translated to associative arrays, but if you happen +to know that the index is always going to be numeric you could change +the {...} to [...]. +Iteration over an associative array is done with each(), but +iteration over a numeric array is NOT. +You need a for loop, or while loop with a pop() or shift(), so you might +need to modify any loop that is iterating over the array in question. +.PP +Arrays which have been split into are assumed to be numerically indexed. +The usual perl idiom for iterating over such arrays is to use pop() or shift() +and assign the resulting value to a variable inside the conditional of the +while loop. +This is destructive to the array, however, so a2p can't assume this is +reasonable. +A2p will write a standard for loop with a scratch variable. +You may wish to change it to a pop() loop for more efficiency, presuming +you don't want to keep the array around. +.PP +Awk starts by assuming OFMT has the value %.6g. +Perl starts by assuming its equivalent, $#, to have the value %.20g. +You'll want to set $# explicitly if you use the default value of OFMT. +.PP +Near the top of the line loop will be the split operation that is implicit in +the awk script. +There are times when you can move this down past some conditionals that +test the entire record so that the split is not done as often. +.PP +There may occasionally be extra parentheses that you can remove. +.PP +For aesthetic reasons you may wish to change the array base $[ from 1 back +to the default of 0, but remember to change all array subscripts AND +all substr() and index() operations to match. +.PP +Cute comments that say "# Here is a workaround because awk is dumb" are not +translated. +.PP +Awk scripts are often embedded in a shell script that pipes stuff into and +out of awk. +Often the shell script wrapper can be incorporated into the perl script, since +perl can start up pipes into and out of itself, and can do other things that +awk can't do by itself. +.SH ENVIRONMENT +A2p uses no environment variables. +.SH AUTHOR +Larry Wall <lwall@devvax.Jpl.Nasa.Gov> +.SH FILES +.SH SEE ALSO +perl The perl compiler/interpreter +.br +s2p sed to perl translator +.SH DIAGNOSTICS +.SH BUGS +It would be possible to emulate awk's behavior in selecting string versus +numeric operations at run time by inspection of the operands, but it would +be gross and inefficient. +Besides, a2p almost always guesses right. +.PP +Storage for the awk syntax tree is currently static, and can run out. +.rn }` '' |