I recently needed to check to see if a file had a particular tag in it before continuing, but I didn’t want to have to read it line by line to find out.

To my astonishment, there is no simple way to read a whole file into a string in Perl. The simple solution would be to use File::Slurp, but since the script will be running in a closed system I could only use default libraries. Also, because it’s Perl, I wanted to do it in a single line to maintain maximum incomprehensibility.

After a bit of tooling around I came up with this:

#!/usr/bin/perl -w

use strict;
use warnings;

# Check the file to ensure it contains the tag before continuing
my $FILE = $ARGV[0] or die $!;
die "File is missing required TIMESTAMP tag.n" unless do { local $/; local @ARGV = $FILE; <> } =~ /TIMESTAMP/;
...

More simply, here is the code to just stick the file contents in a variable:

my $contents = do { local $/; local @ARGV = $FILE; <> };

Essentially, what’s going on here is that I’m unsetting ‘$/’, the Input Record Separator, to make <> give the whole file at once.

Props to Stack Overflow for pointing me in the right direction.