grep is a powerful command-line tool used for searching text using patterns. It's widely used for finding specific text within files or output streams.
grep [options] pattern [file...]
Example file
# example.txt
Hello World
This is a sample file
Bash scripting is powerful
Learning grep, awk, and sed
Another line with the word World
Simple Search:
$ grep "awk" example.txt
Learning grep, awk, and sed
Case-Insensitive Search:
$ grep -i "AWK" example.txt
Learning grep, awk, and sed
The -i option makes the search case-insensitive.
Search in Multiple Files:
$ grep "awk" example.txt hello.txt
example.txt:Learning grep, awk, and sed
Recursive Search in Directories:
grep -r "search_term" /path/to/directory
The -r option searches recursively through all files in the specified directory.
Display Line Numbers:
$ grep -n "awk" example.txt hello.txt
example.txt:4:Learning grep, awk, and sed
The -n option shows the line numbers of matching lines.
Show Only Matching Part of Line:
$ grep -o awk example.txt
awk
Count Matches:
$ grep -c awk example.txt
1
The -c option counts the number of matching lines.
Invert Match:
$ grep -v awk example.txt
Hello World
This is a sample file
Bash scripting is powerful
Another line with the word World
The -v option selects lines that do not match the pattern.
Use Regular Expressions:
grep -E "^Learning" example.txt
Learning grep, awk, and sed
The -E option allows the use of extended regular expressions.
Try
mkdir -p test_dir
echo "Test file" > test_dir/file1.txt
echo "Another test file" > test_dir/file2.txt
grep -r "test" test_dir
test_dir/file2.txt:Another test file
echo -e "abc123\nabc456\n789" > regex_example.txt
grep -E "[0-9]{3}" regex_example.txt
abc123
abc456
789
echo -e "apple\nbanana\ncherry\napple pie" > regex_example.txt
# Search for lines containing "apple" followed by any character:
grep -E "apple." regex_example.txt
apple pie
Script example
#!/bin/zsh
echo "Enter the search term: "
read search_term
echo "Enter the file name: "
read file_name
if [ -f "$file_name" ]; then
count=$(grep -c "$search_term" "$file_name")
echo "The term '$search_term' appears $count times in $file_name."
else
echo "File $file_name does not exist."
fi
Advance usage
Search for a word and show 2 lines of context before and after each match
grep -C 2 "search_term" filename
Search for Whole Words Only
Search for whole words only (not as part of another word)
grep -w "search_term" filename