Mastering the Text Trio: grep, sed, and awk for Powerful Linux Text Processing

Text Trio: grep, sed, awk

grep

Concept

grep is a powerful text search tool that uses pattern matching (including regular expressions) to search files and outputs matching lines by default.

Syntax

grep [options] pattern file

Options

-i   ignore case
-n   show line numbers
-c   count matching lines
-v   invert match
-o   show only matching part
-q   quiet mode
-A N after‑context
-B N before‑context
-C N context
-E   use extended regular expressions (egrep)
-F   fixed strings (fgrep)

Regular Expressions

Regular expressions are patterns composed of literal and special characters used to match strings. They include metacharacters, character classes, quantifiers, anchors, groups, and backreferences, and are supported by many programming languages.

Metacharacters

. matches any single character

[] character class

[^] negated class

[:alnum:], [:alpha:], [:lower:], [:upper:], [:blank:], [:space:], etc.

\w word character, \W non‑word, \s whitespace, \S non‑whitespace

Quantifiers

* 0 or more (greedy)

+ 1 or more

? 0 or 1

{n} exactly n

{m,n} between m and n

{n,} at least n

Anchors

^ start of line

$ end of line

\b word boundary

\< and \> word start/end (POSIX)

Groups

Parentheses ( ) group patterns; backreferences \1, \2 refer to captured groups.

sed

sed is a stream editor that reads input line by line, applies editing commands, and outputs the result.

Syntax

sed [options] 'script' [file]

Common Options

-n   suppress automatic printing
-e   add script commands
-f   read script from file
-r, -E   use extended regular expressions
-i.bak   edit files in place with backup

Addressing

Commands can be prefixed by an address or range (line numbers, regex, etc.). Examples:

1,5p          # print lines 1 to 5
/START/,/END/p   # print from line matching START to line matching END
3~2p          # print every 2nd line starting at line 3

Commands

p print pattern space

d delete matching lines

a\text append after line

i\text insert before line

c\text replace line

w file write matching lines to file

r file read file into output

= print line number

! apply command to non‑matching lines

q quit

awk

awk is a pattern‑action language for processing and reporting text, often used for column‑wise operations.

Usage

awk [options] 'program' file

Important Variables

FS field separator (default whitespace)

OFS output field separator

NF number of fields in current record

NR record number

$0 entire current line

$n nth field

FILENAME name of current file

RS record separator (default newline)