How to check if a file exists in Perl?

Checking if a file exists is a very common task in Perl, especially when working with file input/output (I/O). Perl provides a set of built-in file test operators which make it easy to check various attributes of files, including whether they exist or not.

Using the -e File Test Operator

The simplest way to check if a file exists in Perl is by using the -e file test operator. It returns true if the file (or directory) specified in its operand exists on the filesystem, otherwise it returns false.

This operator works by taking a filename or path as an argument. You can use it with a string filename or a variable holding the filename. For example:

if (-e "somefile.txt") {
    print "File exists\n";
} else {
    print "File does not exist\n";
}

Complete Example

Here is a short complete script that reads a filename from the command line argument and checks if that file exists:

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

# Get the filename from the first command line argument
my $filename = shift // '';

if (!$filename) {
    print "Usage: perl - \n";
    exit 1;
}

if (-e $filename) {
    print "File '$filename' exists.\n";
} else {
    print "File '$filename' does not exist.\n";
}

Explanation and Perl Concepts

• File Test Operators: Perl includes a group of unary file test operators starting with a dash (-), such as -e (exists), -r (readable), -w (writable), -x (executable), -f (is file), and more.
• Sigils: The variable $filename uses the scalar sigil $, since a filename is a scalar string.
• TMTOWTDI ("There's More Than One Way To Do It"): You could also check if a file exists by attempting to open it, but using -e is more direct and idiomatic for existence checking.
• Context: The -e operator is used in scalar context to return a simple boolean value (true or false).

Common Gotchas

• -e returns true for both files and directories. If you want to check specifically for a regular file (not a directory), use -f instead.
• The file might be deleted between checking -e and accessing it, so for atomic operations prefer opening the file and handling exceptions.
• On case-insensitive filesystems (like Windows), checking for existence may not behave as strictly as on Unix systems.
• Remember to ensure the filename is not empty or undefined before applying -e.

Summary

Use Perl’s -e file test operator to check if a file or directory exists. It's simple, built-in, and efficient for existence testing without opening the file.

The example above demonstrates a complete reusable script that you can run with:

perl - somefile.txt

to check whether somefile.txt exists.