Bash — Regular Expressions

Basic patterns

#!/bin/bash

# grep with basic regex
grep "pattern" file.txt

# grep with extended regex
grep -E "pattern1|pattern2" file.txt

# grep with fixed string
grep -F "literal" file.txt

Common patterns

#!/bin/bash

# Match email
grep -E "^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$" file.txt

# Match IP address
grep -E "^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$" file.txt

# Match phone number
grep -E "^\+?[0-9]{10,15}$" file.txt

Character classes

#!/bin/bash

# Any digit
grep -E "[0-9]+" file.txt

# Any letter
grep -E "[a-zA-Z]+" file.txt

# Any character
grep -E "." file.txt

# Word character
grep -E "\w+" file.txt

Quantifiers

#!/bin/bash

# Zero or more
grep -E "ab*" file.txt

# One or more
grep -E "ab+" file.txt

# Zero or one
grep -E "ab?" file.txt

# Exactly n
grep -E "ab{3}" file.txt

# Range
grep -E "ab{2,5}" file.txt

sed

#!/bin/bash

# Replace
sed 's/old/new/g' file.txt

# Delete lines
sed '/pattern/d' file.txt

# Insert
sed '3i\New line' file.txt

# In-place editing
sed -i 's/old/new/g' file.txt

awk

#!/bin/bash

# Print columns
awk '{print $1, $3}' file.txt

# Filter
awk '$3 > 100' file.txt

# Custom separator
awk -F',' '{print $1}' file.txt

# Sum column
awk '{sum += $2} END {print sum}' file.txt

Mini Practice

Write Bash code that:

1. Uses grep with basic regex
2. Uses sed for text replacement
3. Uses awk to extract columns
4. Matches an email pattern

Up Next

Congratulations! You've completed the Bash fundamentals. Continue exploring advanced topics like scripting patterns, cron jobs, and system administration.