How to use Grep Command

 

The grep command is one of the most useful tools in Linux/Unix for searching text. It scans files or streams line by line and prints the lines that match a given pattern.

🔑 Basic Syntax

grep [options] pattern [file...]

• pattern → the text or regex you want to search for
• file → the file(s) you want to search in

📘 Common Examples

• Search for a word in a file

  grep "error" logfile.txt
  

  → Shows all lines in logfile.txt containing the word error.

• Case-insensitive search

  grep -i "error" logfile.txt
  

  → Matches Error, ERROR, error, etc.

• Search recursively in a directory

  grep -r "TODO" ./src
  

  → Finds all lines with TODO in files under ./src.

• Show line numbers

  grep -n "main" program.c
  

  → Displays matching lines with their line numbers.

• Count matches

  grep -c "error" logfile.txt
  

  → Prints how many lines contain error.

• Use regex patterns

  grep "^[0-9]" data.txt
  

  → Matches lines starting with a digit.

⚡ Useful Options

Option	Meaning
-i	Ignore case
-n	Show line numbers
-r	Recursive search in directories
-v	Invert match (show lines not matching)
-c	Count matches
-E	Use extended regex (like egrep)

---