How to read an entire file into an array in Perl?

Reading an entire file into an array in Perl is a simple yet powerful technique to process file contents line-by-line. Each element of the resulting array represents one line from the file, including the newline character \n.

Typical Method to Read a File into an Array

The common approach in Perl involves:

• Opening a filehandle in read mode with open.
• Using the filehandle in list context to slurp all lines at once into an array.
• Optionally removing trailing newlines with chomp.
• Closing the filehandle afterwards.

This takes advantage of Perl’s context sensitivity: the angle operator <> returns all remaining lines in list context.

Perl Concepts Highlighted

• Sigils: Arrays use @, so an array variable is @lines.
• Context: Filehandle in list context returns all lines; in scalar context returns one line at a time.
• TMTOWTDI: "There’s More Than One Way To Do It" — this is one clear, idiomatic approach.
• chomp: Removes newline from each element to clean strings for processing.

Runnable Example (with DATA as file input to avoid external files)

#!/usr/bin/perl
use strict;
use warnings;

# Instead of an external file, we simulate a filehandle with DATA
# DATA is a special filehandle to read from the script’s __DATA__ section

my @lines = <DATA>;   # Read all lines into array (includes newlines)
chomp(@lines);            # Remove trailing newlines

foreach my $line (@lines) {
    print "$line\n";
}

__DATA__
First line of data
Second line
Third line here

Explanation

• We use the special DATA filehandle to simulate reading from a file embedded in the script itself. This allows running the code in sandboxed environments that disallow file I/O.
• @lines = <DATA>; reads all the lines at once because <> is in list context.
• chomp(@lines) cleans trailing newlines so printing lines with added newlines is tidy.
• Output prints each line separately, confirming successful reading.

Common Pitfalls

• Not checking if open succeeded can cause silent failures.
• Using the filehandle in scalar context (like $line = <$fh>) reads only one line.
• Reading very large files into arrays can exhaust memory.
• Remember to close filehandles to release resources.

Version Notes

• Lexical filehandles (my $fh) are preferred since Perl 5.6.
• Reading from DATA has been available for decades and works in all stable Perl versions.

By using the DATA section, this example avoids file system dependencies, making it safe for sandboxed execution while demonstrating the standard Perl idiom for reading a full file into an array.