How to search text with grep in Linux

Short answer

grep searches for patterns in text files and streams, supporting regex, line numbers, and context display.

Steps

1. Search a file:

grep "error" log.txt

2. Case-insensitive search:

grep -i "error" log.txt

3. Recursive search:

grep -r "pattern" /var/log/

4. Show line numbers:

grep -n "pattern" file.txt

5. Invert match:

grep -v "pattern" file.txt

Tips

• grep -E (or egrep) enables extended regular expressions.
• grep -C 2 shows 2 lines of context around each match.
• Pipe ps or df into grep to filter output.

Common issues

• Binary files: use -I to ignore or -a to treat as text.
• Recursive symlink loops: use --exclude-dir or -R instead of -r.