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"_" - Reuse of file test results

Using " _ " file test operator, or stat You can reuse the result of the function.

if (-s $file > $size && -A _> $from_last_access) {
  ...
}

You get the size with -s $file, but behind the scenes you call stat. At that time, information other than size is also saved internally. You can use _ to reuse the file information obtained in the first file test.

The only meaning of using _ is performance. You must make a system call to the OS to get information about the file. System calls are generally costly. If you use _, the file information that you have already obtained will be used, so the second system call will be omitted.

Please note that it should only be used in close proximity. If stat is called somewhere, the information will be updated.

Example

This is an example that reuses the result of the file test.

use strict;
use warnings;

# Reuse the result of the file operator (or stat).

# Preparation
my $file = 'a.txt';
unless (-f $file) {
  die "$file does not exist.\n"; # Check for file existence
}

print "1: Check if the file is old and has a large file size\n";
my $size = 1_000_000;
my $from_last_access = 90;

if (-s $file > $size && -A _> $from_last_access) {
  # You can use _ for the second file test.
  print "$file is greater than $size bytes, ".
    "It's been over $from_last_access days since last access.\n\n";
}
else {print "$file did not meet the condition.\n"}