#!/usr/bin/perl -w #---------------------------------------------------------------------------- # Copyright (C) 2001-2003 Ed Halley #---------------------------------------------------------------------------- =head1 NAME unhead - remove the lines before a match from the input stream untail - remove the lines following a match from the input stream =cut # Both 'unhead' and 'untail' are identical; they determine the task from # the $0 perl variable. The scripts can be linked or symlinked or simply # copied, and will still work as long as they have the correct filenames. =head1 SYNOPSIS unhead '--BEGIN MESSAGE--' *.txt untail '--END MESSAGE--' *.txt =head1 DESCRIPTION The historically common C(1) and C(1) commands are for keeping the head or tail of stream input, usually by a count of lines. This pair of scripts differ in two respects: these scripts work on a single regex (regular expression) to find a matching "cut here" point in the text, and these scripts edit text files in place. By default, the first argument should be a regular expression that should match at least once in each subsequent file. If no additional arguments are given, or if the filename is a hyphen (-), then the standard input and standard output streams are assumed. For filenames, each file is processed in turn, creating a backup file with a tilde (~) appended to the original name. The C variant will remove the header above the given match, and write out the tail (including the first matching line). The C variant will remove the trailing below the given match, and only write out the head (not including the first matching line). =cut #---------------------------------------------------------------------------- use warnings; use strict; my $want = ($0 =~ /untail/)? 'head' : 'tail'; my $suffix = '~'; my $pattern = shift(@ARGV); die "First argument should be a regular expression string" if not $pattern; $pattern = qr/$pattern/; @ARGV = ('-') if not @ARGV; exit(main(@ARGV)); #---------------------------------------------------------------------------- sub main { while (@_) { my $inp = *STDIN; my $outp = *STDOUT; my $file = shift; if ($file ne '-') { die if not -w $file; $inp = *FIN; $inp = *FIN; # hush hush warning warning $outp = *FOUT; $outp = *FOUT; unlink($file.$suffix) if -f $file.$suffix; rename($file, $file.$suffix); open($inp, $file.$suffix) or die "Cannot open $file"; open($outp, '>'.$file) or die "Cannot open $file"; } my $have = 'head'; while (<$inp>) { $have = 'tail' if m{$pattern}; print $outp $_ if $want eq $have; } if ($file ne '-') { close($outp); close($inp); } } } __END__ #---------------------------------------------------------------------------- =head1 IDEAS # chop off email routing header info (first empty line) cat email.msg | unhead '^$' # just students from "Danziger, Jane" to "Funicello, Thomas" query-students | sort | unhead '^D' | untail '^G' # keep the center section of a YACC grammar unhead '^%%$' *.y ; untail '^%%$' *.y =head1 BUGS The C variety will discard everything and leave an empty file if no lines match the given pattern. This is not a bug, but worth a warning. In the case of actual files, you still have the tilde backup. The script for both C and C are identical, and one can be a link to the other. The script determines which part to keep based on the script's name. =head1 LICENSE Copyright (C) 2001-2003 Ed Halley This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. For details on the Perl Artistic License, read the F page. =cut