Perl Interview Questions for DevOps Engineers: Practical Concepts, Commands, and Clear Answers

Perl still appears in automation glue code, legacy operational tooling, text-processing pipelines, and CI helper scripts. This guide organizes common Perl interview topics into practical, technically accurate answers so you can explain not just what a feature does, but when to use it in real DevOps work.

Originally published on 2012-05-22; fully revised and updated.

What interviewers are usually testing

Most Perl interview rounds test your ability to safely handle text, files, process execution, and core language semantics (scope, references, context). If you can answer these cleanly, you can usually handle both scripting and production troubleshooting questions.

• One-liners vs full scripts
• Variable scope: my, our, local
• Arrays, hashes, slices, and splice
• Regex, grep, and substitution
• use vs require, strictness, warnings
• File IO, pipelines, and process exit codes

Perl one-liners vs script files

A Perl one-liner is command-line execution using -e. It is great for quick transforms and ad-hoc operations. A script file is better for maintainability, testing, and reuse.

perl -e 'print qq(Hello)'
perl -ne 'print if /ERROR/' app.log
perl -pi.bak -e 's/search_str/replace_str/g' large_file.txtCode language: JavaScript (javascript)

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

while (my $line = <STDIN>) {
    print $line if $line =~ /ERROR/;
}Code language: PHP (php)

flowchart LR
    A[Question or task appears] --> B{Small one step text task}
    B -- yes --> C[Use perl one liner]
    B -- no --> D[Write script file]
    C --> E[Test with sample data]
    D --> E
    E --> F{Needs external module}
    F -- yes --> G[Install from CPAN]
    F -- no --> H[Run in pipeline]
    G --> H

Scope, symbol table behavior, and references

Interviewers often ask about my vs local, symbolic references, and expressions like ${var} and ${'var'}.

use strict;
use warnings;

our $var = 'package';

{
    my $var = 'lexical';
    print $var;
    print chr(10);

    no strict 'refs';
    print ${'var'};
    print chr(10);
}Code language: PHP (php)

In short: $var resolves lexical variables first when declared with my, while ${'var'} is a symbol-table lookup (symbolic reference), which is blocked under use strict 'refs'.

Arrays, hashes, and list operations interviewers expect

Know how to grow/shrink arrays, use slices, and explain splice in list vs scalar context.

my @arr = (10, 20, 30, 40, 50);

my @slice = @arr[1, 3];
splice(@arr, 2, 1, 99, 100);
push @arr, 60;
my $first = shift @arr;
my $last = pop @arr;

@arr = ();
$#arr = -1;Code language: PHP (php)

splice returns removed elements in list context, and the last removed element in scalar context. Also note: stacks are usually push/pop; queues are commonly push/shift.

my %grades = (
    kim    => 96,
    al     => 63,
    rocky  => 87,
    chrisy => 96,
    jane   => 79,
);

for my $name (sort keys %grades) {
    print $name . q( ) . $grades{$name} . chr(10);
}Code language: PHP (php)

Regex, grep, map, and sed-style substitutions

Perl interviews frequently include regex filtering and replacement tasks. Be ready to explain context and intent clearly.

my @list = (1, 'Test', 0, 'foo', 20);
my @has_digit = grep { /[0-9]/ } @list;
my $count = grep { /[0-9]/ } @list;
my @upper = map { uc($_) } @list;Code language: PHP (php)

sed 's/old/new/g' file.txt
perl -pi.bak -e 's/old/new/g' file.txtCode language: JavaScript (javascript)

Reference link preserved from the original post: Perl Operators.

use vs require, strictness, and interpreter switches

use strict;
use warnings;
use JSON qw(encode_json);

require POSIX;
POSIX->import(qw(strftime));

require 'legacy_helpers.pl';Code language: PHP (php)

Common switches worth mentioning in interviews: -e (execute expression), -c (syntax check), -d (debugger), and warning modes (-w or use warnings;). Official strict documentation: perldoc strict.

File handling, process execution, and environment variables

use strict;
use warnings;

open(my $fh, '<', 'checkbook.txt') or die $!;
while (my $record = <$fh>) {
    print $record;
}
close($fh);

$ENV{'PATH'} = '/bin:/usr/bin:/usr/local/bin';
print $^O;Code language: PHP (php)

my $rc = system('ls', '-l');
if ($rc == -1) {
    die 'failed to execute command';
}
my $exit_code = $rc >> 8;
print $exit_code;Code language: PHP (php)

Interview shorthand: system runs a command and returns status information; exec replaces the current process and only returns on failure. die raises an exception and prints a message; exit terminates with a status code.

CPAN and module installation basics

CPAN is the central Perl ecosystem for modules and documentation. Useful links preserved from the original article: CPAN home, CPAN mirrors, and CPAN FAQ.

cpan App::cpanminus
cpanm local::lib
cpanm Module::Name
ppm install DBD-mysqlCode language: CSS (css)

ppm appears in many older interview banks because it was common in ActivePerl workflows.

Best practices for Perl interview prep

• Prefer clear, modern examples using use strict; and use warnings;.
• Explain context behavior (scalar vs list) whenever discussing grep, splice, or return values.
• Avoid symbolic references unless there is a strong reason.
• Use three-argument open and check errors consistently.
• When discussing command execution, mention exit-code handling rather than only success/fail assumptions.
• If a question is old or ambiguous, state the modern recommended approach explicitly.

Rajesh Kumar

I’m Rajesh Kumar, a DevOps, SRE, DevSecOps, Cloud, and Platform Engineering expert passionate about sharing practical knowledge, real-world experiences, and industry best practices. I have worked at Cotocus and regularly write about technology, travel, investing, health, product reviews, and digital marketing through my various platforms.

I publish technical articles at DevOps School, travel stories at Holiday Landmark, stock market insights at Stocks Mantra, health and fitness guidance at My Medic Plus, product reviews at TrueReviewNow, and SEO and digital marketing strategies at Wizbrand.