Overview

grep filters text by matching patterns. It is foundational for troubleshooting logs and processing data.

Syntax

grep [options] pattern [file...]

Arguments

• pattern: The search expression.
• file: Optional files; defaults to stdin.

Options Table

Examples

grep -i "error" /var/log/syslog
journalctl -u nginx | grep -E " 4| 5"

Real-world Usage

Filter application logs for slow requests during incident triage.

Common Mistakes

• Using grep -r at filesystem root.
• Forgetting to quote regex patterns containing spaces.

Performance Notes

Use grep -F for literal strings to improve speed.

Security Considerations

Be careful when grepping sensitive files; avoid leaking data into logs.

Related Commands

rg, awk, sed

Practice Exercises

1. Find all lines containing "timeout" in /var/log.
2. Search case-insensitively for "auth" in a log file.