#!/usr/bin/perl

use Getopt::Std;
use Time::HiRes qw(sleep time);
getopts('svx') or usage();

my $freq = shift || usage();
@ARGV or usage();

while (1) {
  my $start = time();
  warn "Starting at " . localtime($start) . "\n" if $opt_v;
  system(@ARGV);
  my $rc = $?;
  if ($rc & 255) {
    warn "Command terminated with signal " . ($rc & 255) . "; exiting\n";
    exit 1;
  } elsif ($opt_x && ($rc >> 8)) {
    warn "Command failed with exit status " . ($rc >> 8) . "; exiting\n";
    exit 1;
  }
  my $elapsed = time() - $start;
  warn "Completed after $elapsed sec.\n" if $opt_v;
  my $zz = $opt_s ? $freq - $elapsed : $freq;
  sleep $zz if $zz > 0;
}

sub usage {
  print STDERR "Usage: $0 [-s] [-v] [-x] delay command args...

  run command repeatedly, with <delay> secs between end of last run
    and start of next one

  -v  slightly verbose mode
  -x  exit if command fails
  -s  run command <delay> secs after *start* of last run and start of next one
";
  exit 1;
}