Depends on if you want modified time, access time or inode change time.

For modified time which is likely the most common.

if( -M "file.pdl" < -M "file.cxx" ) {
  print "file.pdl is newer\n";
}
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Likewise with -A for access time and -C for inode change time ( which used to be create time hence the C )

These filetests list the files age in days since the start of your perl script execution. This is usually positive for a briefly running script if your dates on the filesystem reflect reality and your clock is correct. Thus by comparing 2 numeric quantities you can make these descisions.

update: mea culpa, changed the text 'negative' to bolded 'positive'. Think days ago.

if ( -M $file1 < -M $file2)  {
    print $file2, ' is older!', $/;
}
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You might also consider reading this perlfunc:_X.

print "Newer\n" if ((stat($filename))[9] > (stat($filename2))[9]);
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print "" . ( (stat($ARGV[0]))[9] <=> (stat($ARGV[1]))[9] )  ."\n";
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I often want to determine if a file is stale based on the date of it's source file. There are two ways to do that. One is with the stat() function while another is with the file test operator '-M'.

Using stat()

use constant MTIME    =>    9;    # File modification time

if ((stat("$BulletinSrc"))[MTIME] > (stat("$BulletinPDF"))[MTIME]) {
    $Text .= " PDF is stale             \"$BulletinPDF\"\n";
    $Errors++;
    }
  else {
    $Text .= " PDF is UP-TO-DATE        \"$BulletinPDF\"\n";
    }
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Using '-M'

if (-M "$BulletinSrc" < -M "$BulletinPDF") {
    $Text .= " PDF is stale             \"$BulletinPDF\"\n";
    $Errors++;
    }
  else {
    $Text .= " PDF is UP-TO-DATE        \"$BulletinPDF\"\n";
    }
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Notice that in one 'if' statement the comparison is greater than while the other is less than. That's because stat() returns the date of the file while '-M' returns the length of time since the file was modified.

                  Start of program
  TDS             :
  :               :
  V               V
  |<----- A ----->|
  |---------------:
                  :
      TDS         :
      :           :
      V           :
      |-----------:
      |<--- B --->|

   length(A) < length(B) means A is stale
   date(A)   > date(B)   means A is stale  (notice start of program is
+ irrelevant!)

i.e., stat() returns a TDS (time date stamp)
      -M returns a length since the start of the program
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For me, I have struggled with this until I understood the details.

I hope this helps.

With error checking:

stat( $qfn )
   or die( "stat: $!\n" );

my $mtime = ( stat _ )[9];
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stat( $qfn )
   or die( "stat: $!\n" );

my $mtime = -M _;
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defined( -M $qfn )
   or die( "stat: $!\n" );
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