UNIX for Dummies Questions & Answers

#!/usr/bin/perl

use POSIX qw(strftime);
my $file = shift @ARGV;
stat $file;
die "File $file does not exist or cannot be read: $!"
  unless -f _ || -r _;
die "File $file cannot be stat'd: $!"
  unless stat _;

# Calculate in seconds the time it was yesterday (24 hours ago) at 7pm.
my $_7pm_last_night = ( strftime "%s",(0,0,19,(localtime(time - 24*60*60))[3..8]));

# compare the file's mtime timestamp with that time and exit accordingly
exit ( (stat(_))[9] > $_7pm_last_night  ?  0  : 1 );

# exits with 0 if the file exists and has been updated since 7pm, 1 otherwise