fgrep — Fixed-string search

A grep variant that matches literal strings without regex interpretation.

Basic Information

What is this command?

fgrep behaves like grep -F and treats the pattern as a literal string rather than a regex. It is handy when the search text contains dots or brackets.

Modern GNU grep recommends grep -F. To search many literals at once, grep -F -f patterns.txt is convenient.

What problems does it solve?

• Searching values with dots such as IP addresses or versions
• Matching log text that contains brackets or asterisks
• Searching many literals from a list file
• Avoiding regex escaping entirely

Key features

Literal matching

Metacharacters are treated as plain characters.

• When to use: Finding values containing dots or brackets
• What you get: Exact matches without escaping.
• Limitations: Regex features are unavailable.

Pattern list

The -f option reads patterns from a file.

• When to use: Checking blocklists or keyword sets
• What you get: One invocation searches many strings.
• Limitations: Blank lines may match every line.

Performance

Literal search uses faster algorithms.

• When to use: Finding plain strings in large logs
• What you get: It is often faster than regex.
• Limitations: Case-insensitive search needs an extra flag.

Installation and usage

Check whether it is installed

fgrep --version

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

Real-world examples

Value with dots

Match an IP address literally.

fgrep '192.168.0.10' access.log

Search with a list

Read several strings from a file.

printf 'ERROR\nFATAL\n' > /tmp/p.txt
fgrep -f /tmp/p.txt app.log

Use grep -F

Run the same search with the recommended syntax.

grep -F '[main]' app.log

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