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

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.

Solution 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.

Solution 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!

Solution 3:

If you're writing a sh script, the most useful way is to use test with the already mentioned stat trick:

if [ `stat --format=%Y $file` -le $(( `date +%s` - 1800 )) ]; then 
    do stuff with your 30-minutes-old $file
fi

Note that [ is a symbolic link (or otherwise equivalent) to test; see man test, but keep in mind that test and [ are also bash builtins and thus can have slightly different behavior. (Also note the [[ bash compound command).

Solution 4:

Ok, no stat and a crippled find. Here's your alternatives:

Compile the GNU coreutils to get a decent find (and a lot of other handy commands). You might already have it as gfind.

Maybe you can use date to get the file modification time if -r works?

(`date +%s` - `date -r $file +%s`) > (30*60)

Alternatively, use the -nt comparision to choose which file is newer, trouble is making a file with a mod time 30 minutes in the past. touch can usually do that, but all bets are off as to what's available.

touch -d '30 minutes ago' 30_minutes_ago
if [ your_file -ot 30_minutes_ago ]; then
    ...do stuff...
fi

And finally, see if Perl is available rather than struggling with who knows what versions of shell utilities.

use File::stat;
print "Yes" if (time - stat("yourfile")->mtime) > 60*30;

Solution 5:

For those like myself, who don't like back ticks, based on answer by @slebetman:

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