Grep Command Cheatsheet
Table of Contents
- Command Structure
- Basic Search Options
- Pattern Matching
- Context Control
- File Handling
- Output Control
- Performance Optimization
- Real-World Examples
- Advanced Techniques
Command Structure
The grep command has two basic syntaxes:
grep [options] pattern [file...]cat [file] | grep [options] pattern- pattern: Text or regular expression to search for
- file: Target files (optional)
- options: Modify search behavior
grep "error" file.log # Search in specific filecat file.log | grep "error" # Search using pipegrep "error" *.log # Search in multiple filesgrep -r "TODO" ./src # Recursive searchBasic Search Options
-i # Case insensitive-w # Match whole words only-x # Match entire lines only-n # Show line numbers-c # Count matching lines-v # Invert match (non-matching lines)-l # List matching files only-L # List non-matching files onlygrep -i "error" file.log # Case-insensitive searchgrep -w "log" file.txt # Whole word "log" onlygrep -n "TODO" *.py # Show line numbersgrep -v "^#" config.txt # Lines not starting with #Pattern Matching
-E # Extended regex (egrep)-F # Fixed strings (fgrep)-P # Perl regex syntax-e # Multiple patterns^ # Start of line$ # End of line. # Any single character* # Zero or more occurrences+ # One or more occurrences (with -E)? # Zero or one occurrence (with -E)[] # Character class[^] # Negated character classgrep -E "error|warning" file.log # Multiple patternsgrep "^#" config.txt # Lines starting with #grep -E "\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}\b" -i file.txt # Email addressesgrep -P "\d{3}-\d{2}-\d{4}" file.txt # SSN pattern with Perl regexContext Control
-A n # Show n lines after match-B n # Show n lines before match-C n # Show n lines before and aftergrep -A 3 "error" file.log # Error + 3 lines aftergrep -B 2 "exception" file.log # Exception + 2 lines beforegrep -C 1 "warning" file.log # Warning + 1 line before & afterFile Handling
-r # Recursive search-R # Recursive (follow symlinks)--include # Include only certain files--exclude # Exclude certain filesgrep -r "TODO" ./srcgrep -R "error" /var/loggrep --include="*.py" -r "def" .grep --exclude="*.log" -r "error" .grep --exclude-dir={.git,node_modules} -r "TODO"Output Control
-o # Show only matched parts-h # Suppress filename prefix-H # Show filename prefix--color # Colorize outputgrep -o "error.*" file.log # Only matching textgrep -h "pattern" *.txt # No filenamesgrep -H "pattern" single.txt # Force filenamegrep --color=auto "error" file.log # Colored outputPerformance Optimization
-
Use Fixed Strings When Possible
Terminal window grep -F "literal string" large_file.txt -
Limit Directory Search
Terminal window grep --exclude-dir={.git,node_modules,dist} -r "pattern" -
Use Count for Large Files
Terminal window grep -c "pattern" huge_file.txt
Real-World Examples
# Find errors and their contextgrep -B2 -A1 "ERROR" /var/log/syslog
# Count errors by typegrep -o "ERROR:[^ ]*" logs.txt | sort | uniq -c
# Find IP addressesgrep -E "\b([0-9]{1,3}\.){3}[0-9]{1,3}\b" access.log# Find TODO commentsgrep -r "TODO\|FIXME" --include="*.{js,py,cpp}" .
# Find function definitionsgrep -r "^[[:space:]]*def.*" --include="*.py" .
# Find deprecated API usesgrep -r "deprecated" --include="*.java" .# Monitor auth attemptsgrep "Failed password" /var/log/auth.log
# Check configurationgrep -v "^#" /etc/ssh/sshd_config | grep .
# Find large queriesgrep "slow query" /var/log/mysql/mysql-slow.logAdvanced Techniques
Pipeline Operations
# Search and replacegrep -l "old_text" *.txt | xargs sed -i 's/old_text/new_text/g'
# Complex filtersgrep "error" log.txt | grep -v "debug" | sort | uniq -c
# Compressed fileszcat *.gz | grep "pattern"Combining with Other Tools
# With findfind . -type f -exec grep "pattern" {} +
# With awkgrep "pattern" file.txt | awk '{print $2}'
# With xargsgrep -l "pattern" *.txt | xargs cp -t /backup/Be careful with recursive searches in large directories. Use --exclude-dir for better performance.