grep (Global Regular Expression Print)

grep is a powerful command-line utility used for searching plain-text data sets for lines that match a regular expression. It is commonly used for searching through files and output from other commands.

Basic Syntax

grep [options] pattern [file...]

Commonly Used Options

-i: Ignore case distinctions in patterns and data.
-v: Invert the sense of matching, to select non-matching lines.
-c: Count the number of matching lines.
-l: List only the names of files with matching lines.
-L: List only the names of files without matching lines.
-n: Prefix each line of output with the line number within its input file.
-H: Print the file name for each match.
-h: Suppress the file name prefix on output.
-r or -R: Read all files under each directory, recursively.
-w: Select only those lines containing matches that form whole words.
-x: Select only those matches that exactly match the whole line.
-A num: Print num lines of trailing context after matching lines.
-B num: Print num lines of leading context before matching lines.
-C num: Print num lines of output context (both before and after).

Examples

Basic Search

Search for the pattern "foo" in a file:

grep 'foo' file.txt

Ignore Case

Search for the pattern "foo" in a file, ignoring case:

grep -i 'foo' file.txt

Invert Match

Search for lines that do not contain the pattern "foo":

grep -v 'foo' file.txt

Count Matches

Count the number of lines that contain the pattern "foo":

grep -c 'foo' file.txt

List Matching Files

List the names of files that contain the pattern "foo":

grep -l 'foo' *.txt

List Non-Matching Files

List the names of files that do not contain the pattern "foo":

grep -L 'foo' *.txt

Show Line Numbers

Show line numbers for lines that contain the pattern "foo":

grep -n 'foo' file.txt

Recursive Search

Search for the pattern "foo" in all files under the current directory, recursively:

grep -r 'foo' .

Whole Word Match

Search for the whole word "foo":

grep -w 'foo' file.txt

Exact Line Match

Search for lines that exactly match "foo":

grep -x 'foo' file.txt

Context Lines

Print 2 lines of context before and after matching lines:

grep -C 2 'foo' file.txt

Print 2 lines of context after matching lines:

grep -A 2 'foo' file.txt

Print 2 lines of context before matching lines:

grep -B 2 'foo' file.txt

Conclusion

grep is a versatile tool for searching text using patterns. Understanding its options and commands allows for efficient and powerful text searching directly from the command line.

Last modified: 14 December 2024