How to Use grep to Search File Contents

grep searches for text patterns within files. It's one of the most powerful Linux tools.

Basic Search

grep "search term" filename

Useful Options

# Case-insensitive
grep -i "error" /var/log/syslog

# Recursive (search directories)
grep -r "TODO" /var/www/

# Show line numbers
grep -n "function" script.py

# Show context (lines before/after)
grep -C 3 "error" logfile

# Invert match (lines NOT matching)
grep -v "debug" logfile

# Count matches
grep -c "error" logfile

Regular Expressions

# Lines starting with "Error"
grep "^Error" logfile

# Lines ending with a number
grep "[0-9]$" logfile

# IP addresses (basic)
grep -E "[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}" logfile