#!/usr/bin/perl -w

use strict;
use Fcntl ':flock';
use IO::Seekable;

die "usage: $0 line files..." if @ARGV < 2;
my ($line, @files) = @ARGV;
foreach my $f (@files) {
    open(F, "+<$f") or die "cannot open $f: $!";
    flock(F, LOCK_EX) or die "cannot lock $f: $!";
    chomp (my @lines = <F>);
    my $seen = 0;
    my @out;
    foreach (@lines) {
	push @out, $_
	  unless $_ eq $line and not $seen++;
    }

    die "line $line not found in $f" if not $seen;
    
    truncate F, 0 or die "cannot truncate $f: $!";
    seek F, 0, SEEK_SET or die "cannot seek on $f: $!";
    foreach (@out) {
	print F "$_\n" or die "cannot write to $f: $!";
    }

    close F or die "cannot close $_: $!";
}