Best way to check a file content is changed or not with perl?

Question

There is a dynamic file which will be generated before my script executing.

my $file = a.txt;

Here i want to check:

(Is content of $file changed)? Do_something: Skip;

I'm looking for some solution as below:

• if ( if_modified( $file );

  --> But We need an initialization file and compare with the latest file while here we have only 1 file at a time.

• $monitor->watch( $file ); Is it able to do my task?

• I guess that using checksum is not needed because after that i also need to see if checksum result is changed or not.

Answer 1

There are a few possibilities:

• https://metacpan.org/pod/File::Monitor
• https://metacpan.org/pod/File::Modified

And Linux-specififc:

• https://metacpan.org/pod/Linux::Inotify2

as mentioned by @choroba

Answer 2

The Perl file operators and the stat function also tell you when a file was last changed (it's modification time) . The common approach is to check against some reference file, that is whether a file was changed later than the reference file, or to check when a file was changed relative to the script start.

Get the time when a file was last modified

my $last_modified = (stat $filename)[9];

if( $last_modified >= $other_modified ) {
    # file changed since we last checked ...
    $other_modified = $last_modified;
};

Check if a file was modified some days ago:

if( -M $filename > 5 ) {
    print "'$file' was modified at least 5 days ago\n";
};

See also

stat , the -M function