flock.pl

#!/usr/bin/perl -T
#
#  Author: Hari Sekhon
#  Date: 2012-02-02 13:24:30 +0000 (Thu, 02 Feb 2012)
#
#  https://github.com/harisekhon/tools
#
#  License: see accompanying Hari Sekhon LICENSE file
#
#  If you're using my code you're welcome to connect with me on LinkedIn
#  and optionally send me feedback to help improve or steer this or other code I publish
#
#  https://www.linkedin.com/in/harisekhon
#

$DESCRIPTION = "Arbitrary locking utility. Useful for safely running commands that would otherwise clash";

$VERSION = "1.2.1";

use strict;
use warnings;
use File::Basename;
use Getopt::Long qw(:config bundling);
use Fcntl ':flock';

BEGIN {
    delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};
    $ENV{'PATH'} = '/bin:/usr/bin';
    $| = 1; 
}

my $progname = basename $0;

my $command;
my $default_timeout = 10;
my $help;
my $lockfile;
my $max_timeout = 3600;
my $timeout = $default_timeout;
my $verbose = 0;
my $version;

sub vlog{
    print "@_\n" if $verbose;
}

sub usage {
    print STDERR "@_\n\n" if @_;
    print STDERR "$main::DESCRIPTION\n\n" if $main::DESCRIPTION;
    print STDERR "usage: $progname [ options ]

    -c --command        Command to run if lock succeeds
    -l --lockfile       Lockfile to use. This will be created if it doesn't exist, will not be overwritten or appended to and will not be removed for safety
    -t --timeout        Timeout in secs (default $default_timeout)
    -v --verbose        Verbose mode
    -V --version        Print version and exit
    -h --help --usage   Print this help
\n";
    exit 3;
}

GetOptions (
            "c|cmd|command=s"   => \$command,
            "l|lock|lockfile=s" => \$lockfile,
            "h|help|usage"      => \$help,
            "t|timeout=i"       => \$timeout,
            "v|verbose+"        => \$verbose,
            "V|version"         => \$version,
           ) or usage;

defined($help) and usage;
defined($version) and die "$progname version $main::VERSION\n";
defined($command)  || usage "command not specified";
defined($lockfile) || usage "lockfile not specified";

# Allow all chars for cmd since this is the point of the code
$command =~ /^(.+)$/;
$command = $1;
$lockfile =~ /^([\/\w\s_\.\*\+-]+)$/ or die "Invalid lockfile specified, did not match regex\n";
$lockfile = $1;
$timeout =~ /^\d+$/ || usage "timeout value must be a positive integer\n";
($timeout >= 1 && $timeout <= $max_timeout) || usage "timeout value must be between 1 - $max_timeout secs\n";

vlog "verbose mode on";
$SIG{ALRM} = sub {
    die "timed out after $timeout seconds\n";
};
vlog "setting timeout to $timeout secs\n";
alarm($timeout);

my $tmpfh;
if(-f $lockfile){
    vlog "opening lock file '$lockfile'\n";
    open $tmpfh, "<", $lockfile or die "Error: failed to open lock file '$lockfile': $!\n";
} else {
    vlog "creating lock file '$lockfile'\n";
    open $tmpfh, "+>", $lockfile or die "Error: failed to create lock file '$lockfile': $!\n";
}
flock($tmpfh, LOCK_EX | LOCK_NB) or die "Failed to aquire a lock on lock file '$lockfile', another process must be running, aborting\n";
system($command);
exit $? >> 8;