How can I tell if a file is older than 30 minutes from /bin/sh?

Question

How do I write a script to determine if a file is older than 30 minutes in /bin/sh?

Unfortunately does not the stat command exist in the system. It is an old Unix system, http://en.wikipedia.org/wiki/Interactive_Unix

Perl is unfortunately not installed on the system and the customer does not want to install it, and nothing else either.

Answer 1

Here's one way using find.

if test "`find file -mmin +30`" 

The find command must be quoted in case the file in question contains spaces or special characters.

Answer 2

The following gives you the file age in seconds:

echo $(( `date +%s` - `stat -L --format %Y $filename` )) 

which means this should give a true/false value (1/0) for files older than 30 minutes:

echo $(( (`date +%s` - `stat -L --format %Y $filename`) > (30*60) )) 

30*60 -- 60 seconds in a minute, don't precalculate, let the CPU do the work for you!