Perl Command Line Guide — One-Liners and CLI Scripting Techniques

In this tutorial, you will learn about Perl Command Line Guide. We cover key concepts, practical examples, and best practices to help you master this topic.

Perl command-line flags enable powerful one-liners for text processing -- -e for inline code, -p for automatic print loop, -n for non-printing loop, -a for auto-split into @F, -F to set field delimiter, and -i for in-place file editing.

Basic One-Liners

# Execute code
perl -e 'print "Hello, World!\n"'

# With strict and warnings
perl -Mstrict -Mwarnings -e 'my $x = 42; print $x'

# Print file lines
perl -pe '$_' file.txt

# Print lines containing pattern
perl -ne 'print if /error/' log.txt

In-Place Editing

# Backup and replace
perl -i.bak -pe 's/old/new/g' file.txt

# In-place without backup
perl -i -pe 's/\s+$//' *.txt  # trim trailing whitespace

# Multiple files
perl -i.bak -pe 's/copyright 2025/copyright 2026/g' *.html

Auto-Split Mode

# Print first column (default: split on whitespace)
perl -ane 'print "$F[0]\n"' data.txt

# Custom delimiter
perl -F: -ane 'print "$F[0]\n"' /etc/passwd

# CSV processing
perl -F, -ane 'print "$F[1]\n"' data.csv

Common Patterns

# Line count
perl -ne 'END { print "$.\n" }' file.txt

# Remove duplicate lines
perl -ne 'print unless $seen{$_}++' file.txt

# Sum a column
perl -ane '$sum += $F[1]; END { print "$sum\n" }' data.txt

# Extract emails
perl -ne 'print "$_\n" while /([\w.]+@\w+\.\w+)/g' file.txt

Common Mistakes

1. Single vs double quotes on Windows

On Windows, use double quotes: perl -e "print 'hello'". Single quotes don't protect $variables.

2. Forgetting -i creates backup

-i.bak creates .bak backups. Use -i alone for no backup (dangerous). Always test without -i first.

3. -a without -n or -p

-a (auto-split) requires -n or -p to create the implicit loop. Alone, it does nothing.

Practice Questions

1. What does -pe do? -p creates a print loop (prints $_ after each iteration). -e provides inline code.

2. How do you edit a file in-place with backup? perl -i.bak -pe 's/old/new/g' file.txt. Original is saved as file.txt.bak.

3. What does @F contain with -a? @F contains the fields of the current input line, split on whitespace (or the -F delimiter).

FAQ

{{< faq question="Can I run multi-line scripts from command line?" >}} Yes, separate with newlines or semicolons: perl -e 'my $x = 5; print $x'. {{< /faq >}}

{{< faq question="What does -MO=Deparse do?" >}} Shows how Perl compiles your code: perl -MO=Deparse -e 'print "hello"'. Useful for understanding optimization. {{< /faq >}}

{{< faq question="How do I use modules in one-liners?" >}} -M loads a module: perl -MData::Dumper -e 'print Dumper(\%ENV)'. {{< /faq >}}

What's Next

Now learn about debugging Perl code.