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| -rw-r--r-- | doc/textutils.texi | 77 |
1 files changed, 76 insertions, 1 deletions
diff --git a/doc/textutils.texi b/doc/textutils.texi index 57bb8e007..7b27e1e4c 100644 --- a/doc/textutils.texi +++ b/doc/textutils.texi @@ -1813,7 +1813,7 @@ option has the form @samp{@var{f}.@var{c}}, where @var{f} is the number of the field to use and @var{c} is the number of the first character from the beginning of the field (for @samp{+@var{pos}}) or from the end of the previous field (for @samp{-@var{pos}}). If the @samp{.@var{c}} -is omitted, it's taken to be the first character in the field. If the +is omitted, it is taken to be the first character in the field. If the @samp{-b} option was specified, the @samp{.@var{c}} part of a field specification is counted from the first nonblank character of the field (for @samp{+@var{pos}}) or from the first nonblank character following @@ -1830,6 +1830,81 @@ from the global options it will be attached to both. If a @samp{-n} or @samp{-@var{pos}} parts of a key specification. Keys may span multiple fields. +Here are some examples to illustrate various combinations of options. +In them, the POSIX @samp{-k} option is used to specify sort keys rather +than the obsolete @samp{+@var{pos1}-@var{pos2}} syntax. + +@itemize @bullet + +@item +Sort in descending (reverse) numeric order. + +@example +sort -nr +@end example + +Sort alphabetically, omitting the first and second fields. +This uses a single key composed of the characters beginning +at the start of field three and extending to the end of each line. + +@example +sort -k3 +@end example + +@item +Sort numerically on the second field and resolve ties by sorting +alphabetically on the third and fourth characters of field five. +Use @samp{:} as the field delimiter. + +@example +sort -t : -k 2,2n -k 5.3,5.4 +@end example + +Note that if you had written @samp{-k 2} instead of @samp{-k 2,2} +@samp{sort} would have used all characters beginning in the second field +and extending to the end of the line as the primary @emph{numeric} +key. For the large majority of applications, treating keys spanning +more than one field as numeric will not do what you expect. + +Also note that the @samp{n} modifier was applied to the field-end +specifier for the first key. It would have been equivalent to +specify @samp{-k 2n,2} or @samp{-k 2n,2n}. All modifiers except +@samp{b} apply to the associated @emph{field}, regardless of whether +the modifier character is attached to the field-start and/or the +field-end part of the key specifier. + +@item +Sort the password file on the fifth field and ignore any +leading white space. Sort lines with equal values in field five +on the numeric user ID in field three. + +@example +sort -t : -k 5b,5 -k 3,3n /etc/passwd +@end example + +An alternative is to use the global numeric modifier @samp{-n}. + +@example +sort -t : -n -k 5b,5 -k 3,3 /etc/passwd +@end example + +Finally, to ignore both leading and trailing white space, you +could have applied the @samp{b} modifier to the field-end specifier +for the first key, + +@example +sort -t : -n -k 5b,5b -k 3,3 /etc/passwd +@end example + +or by using the global @samp{-b} modifier instead of @samp{-n} +and an explicit @samp{n} with the second key specifier. + +@example +sort -t : -b -k 5,5 -k 3,3n /etc/passwd +@end example + +@end itemize + @node uniq invocation @section @code{uniq}: Uniqify files |