tailfgrep

#!/usr/bin/env perl
#
# tailfgrep -- monitor a file a la tail -f, looking for a given regexp
# Copyright (c) 1999 Adam Spiers <adam@spiers.net>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

# TODO:
#   - extend to multiple patterns (one for each file?)
#   - include more options from tail (e.g. -n) and grep (e.g. -i)

use strict;
use warnings;

use Getopt::Long;

my ($quiet, $inverse, $match) = (0, 0, 0);
GetOptions(
           "quiet|q" => \$quiet,
           "inverse|v" => \$inverse,
           "match|m" => \$match,
          );

unless (@ARGV) {
  die <<EOF;
Usage: tailfgrep [ options ] <Perl regexp> <file1> [ <file2> [ <file3> ... ] ]
   -m, --match    --  echo everything to STDOUT, exit when first match found
   -q, --quiet    --  quiet mode, same as grep -q; don't print matches,
                      exit when first match found
   -v, --inverse  --  inverse mode (print lines which don't match)
EOF
}

my ($re, @files) = @ARGV;

my %fh = ();
open_files();

$| = 1;

my $last_file = '';

while (1) {
 FILE:
  foreach my $file (@files) {
    my $fh = $fh{$file};
    while (defined($_ = <$fh>)) {
      if ($quiet) {
        exit 0 if match($_);
      }
      elsif ($match) {
        output_line($file);
        exit 0 if match($_);
      }
      else {
        output_line($file) if match($_);
      }
    }
    seek($fh, 0, 1); # clear EOF
  }
  sleep 1;
}

close_files();

sub open_files {
  if (! @files && -t 1) {
    push @files, '-';
  }

  foreach my $file (@files) {
    if ($file eq '-') {
      $fh{$file} = *STDIN;
      next;
    }

    -f $file or die "$file isn't a file.\n";
    local *FH;
    open(FH, $file) or die "Couldn't open $file: $!\n";
    seek(FH, 0, 2);
    $fh{$file} = *FH;
  }
}

sub close_files {
  foreach my $file (@files) {
    my $fh = $fh{$file};
#    warn "closing $file / $fh\n";
    close($fh);
  }
}

sub match {
  my ($line) = @_;
  return ($line =~ /$re/) ^ $inverse;
}

sub output_line {
  my ($file) = @_;

  $file = 'STDIN' if $file eq '-';

  if (@files > 1) {
    if ($file ne $last_file) {
      print "\n==> $file <==\n\n";
    }
    print;
    $last_file = $file;
  }
  else {
    print;
    $last_file = $file;
  }
}