egrep — Extended regex search

A grep variant that uses extended regular expressions.

Basic Information

What is this command?

egrep behaves like grep -E. Extended regex metacharacters such as +, ?, | and () work without backslashes.

Modern GNU grep discourages egrep and recommends grep -E. New scripts should use grep -E for portability and maintainability.

What problems does it solve?

• Matching one of several alternatives
• Specifying repetition counts with {n,m}
• Combining groups and alternation
• Understanding egrep calls in legacy scripts

Key features

Extended regex

Use +, ?, | and () without escaping.

• When to use: Writing complex conditions concisely
• What you get: Patterns become easier to read.
• Limitations: Syntax differs from basic grep and can confuse.

Multiple patterns

Alternation matches several options at once.

• When to use: Finding errors and warnings together
• What you get: Reduces multiple calls to one.
• Limitations: Without grouping, precedence may differ from intent.

Portability

Prefer grep -E for new code.

• When to use: Maintaining scripts long term
• What you get: Avoids deprecation warnings.
• Limitations: Some very old systems only provide egrep.

Installation and usage

Check whether it is installed

egrep --version

sudo apt install grep # Debian/Ubuntu sudo dnf install grep # Fedora

Real-world examples

Alternation

Match either of two strings.

egrep 'error|warning' app.log

Repetition

Match three digits.

egrep '[0-9]{3}-[0-9]{4}' contacts.txt

Use grep -E

Run the same query with the recommended syntax.

grep -E '^(GET|POST) ' access.log | head

Source (HTML): https://games.aidebatehub.com/programs/linux/basics/egrep.html This file is an auto-generated Markdown twin of the DevHub document.