Master grep: Essential Linux Text Search Commands and Tips

Introduction

The article introduces grep , a fundamental Linux command for searching text within files and command output, complementing earlier tutorials on other Linux utilities.

Common Usage

Typical usage combines grep with a pipe ( |) to filter the output of previous commands. Example: $ ps -ef | grep redis This filters the process list to show only lines containing redis. The -v option excludes matching lines, and -c returns a count:

$ ps -ef | grep redis | grep -v auto

$ ps -ef | grep redis -c

Searching File Contents

To search within a specific file, use: $ grep "test" aaa/bbb/linux_command_debug.md Adding -n shows line numbers:

$ grep -n "test" aaa/bbb/linux_command_debug.md

Searching Multiple Files or Excluding Files

Search all .md files: $ grep -n "test" *.md Exclude files with --exclude or directories with --exclude-dir:

$ grep -rn "test" --exclude=*.txt

$ grep -rn "test" --exclude-dir=aaa

Multiple exclusion patterns can be stored in a file and referenced with --exclude-from:

$ grep -rn "test" --exclude-from=skip.txt

Finding Files Containing a Keyword

Recursively list files that contain a pattern using -l (or --file-with-matches):

$ grep -rln "int main(void)"

Finding Files Not Containing a Keyword

Use -L to list files that do not match the pattern:

$ grep -rLn "int main(void)"

Case‑Insensitive Search

Apply -i (or --ignore-case) to ignore case:

$ grep -rni "int MAIN(void)"

Showing Context Lines

Show lines before and after a match with -B and -A (or --before-context / --after-context):

$ grep -rn "int main(void)" -A 1 -B 1

Using a Rule File

Store multiple patterns in a file (e.g., key.txt) and search with -f:

$ cat filename | grep -f key.txt

Regular‑Expression Search

grep

supports regular expressions. For example, to find lines that start and end with t: $ grep -rn ^t.*t$ Extended regular expressions can be used via egrep.

Summary of Frequently Used Options

-v Show lines that do NOT match the pattern.

-l List files containing matches.

-L List files without matches.

-r Recursive search.

-i Ignore case.

-n Show line numbers.

-A n Show n lines after a match.

-B n Show n lines before a match.

--exclude Exclude specific files.

--exclude-dir Exclude specific directories.

-f Read patterns from a file.