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#!/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 fr +om # the $0 perl variable. The scripts can be linked or symlinked or sim +ply # copied, and will still work as long as they have the correct filenam +es. =head1 SYNOPSIS unhead '--BEGIN MESSAGE--' *.txt untail '--END MESSAGE--' *.txt =head1 DESCRIPTION The historically common C<head>(1) and C<tail>(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 sho +uld match at least once in each subsequent file. If no additional argumen +ts 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<unhead> variant will remove the header above the given match, an +d write out the tail (including the first matching line). The C<untail> 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 $pat +tern; $pattern = qr/$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<unhead> 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<unhead> and C<untail> are identical, and one can + be a link to the other. The script determines which part to keep based o +n the script's name. =head1 LICENSE Copyright (C) 2001-2003 Ed Halley <ed@halley.cc> This program is free software; you can redistribute it and/or modify i +t under the same terms as Perl itself. For details on the Perl Artistic License, read the F<http://www.perl.com/language/misc/Artistic.html> page. =cut

In reply to unhead and untail by halley

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