Bash Working with Strings

Strings are sequences of characters — letters, numbers, spaces, and symbols. Bash provides many built-in ways to manipulate strings without needing any external tools. This topic covers the most practical string operations used in real-world scripts.

Defining Strings

#!/bin/bash
name="eStudy247"
greeting='Hello World'
mixed="Learning Bash in 2026"

Single quotes vs Double quotes:

String Length

Use ${#variable} to get the number of characters in a string.

#!/bin/bash
word="Bangalore"
echo "Length: ${#word}"

Output:

Length: 9

String Concatenation

Place two variables or strings next to each other to join them.

#!/bin/bash
first="Good"
second="Morning"
combined="$first $second"
echo $combined

Output:

Good Morning

Extracting a Substring

Use ${variable:start:length} to extract a portion of a string. Positions start at 0.

┌──────────────────────────────────────────┐
│  String:   B  a  s  h  S  c  r  i  p  t  │
│  Index:    0  1  2  3  4  5  6  7  8  9  │
└──────────────────────────────────────────┘

#!/bin/bash
text="BashScript"
echo ${text:0:4}    # Start at 0, take 4 chars
echo ${text:4:6}    # Start at 4, take 6 chars

Output:

Bash
Script

String Replacement

Replace the first occurrence of a pattern using ${variable/old/new}. Replace all occurrences using ${variable//old/new}.

#!/bin/bash
sentence="I love cats and cats love fish"

echo ${sentence/cats/dogs}    # Replace first match
echo ${sentence//cats/dogs}   # Replace all matches

Output:

I love dogs and cats love fish
I love dogs and dogs love fish

Converting to Uppercase and Lowercase

#!/bin/bash
text="Hello World"
echo ${text^^}   # Convert to UPPERCASE
echo ${text,,}   # Convert to lowercase
echo ${text^}    # Capitalize first letter only

Output:

HELLO WORLD
hello world
Hello World

Removing Parts of a String

Remove Prefix (from the beginning)

#!/bin/bash
filename="report_2026.csv"
echo ${filename#report_}   # Remove shortest match from start

Output:

2026.csv

Remove Suffix (from the end)

#!/bin/bash
filename="report_2026.csv"
echo ${filename%.csv}   # Remove .csv from end

Output:

report_2026

String Trim Summary Diagram

┌────────────────────────────────────────────────────────┐
│  String: "___hello___"                                 │
│                                                        │
│  ${var#pattern}  → Remove shortest prefix match        │
│  ${var##pattern} → Remove longest prefix match         │
│  ${var%pattern}  → Remove shortest suffix match        │
│  ${var%%pattern} → Remove longest suffix match         │
└────────────────────────────────────────────────────────┘

Checking if a String Contains a Substring

#!/bin/bash
sentence="Bash scripting is powerful"
if [[ "$sentence" == *"scripting"* ]]; then
  echo "Found the word 'scripting'"
fi

Output:

Found the word 'scripting'

Checking if a String Starts or Ends with a Pattern

#!/bin/bash
file="backup_2026.tar.gz"

# Check start
if [[ "$file" == backup* ]]; then
  echo "File is a backup"
fi

# Check end
if [[ "$file" == *.gz ]]; then
  echo "File is compressed"
fi

Output:

File is a backup
File is compressed

Splitting a String

Use the IFS (Internal Field Separator) variable to split a string by a delimiter.

#!/bin/bash
data="John:30:Delhi"
IFS=':' read -ra parts <<< "$data"
echo "Name : ${parts[0]}"
echo "Age  : ${parts[1]}"
echo "City : ${parts[2]}"

Output:

Name : John
Age  : 30
City : Delhi

Comparing Strings

#!/bin/bash
a="apple"
b="orange"

if [ "$a" = "$b" ]; then
  echo "Same"
elif [ "$a" \< "$b" ]; then
  echo "$a comes before $b alphabetically"
else
  echo "$a comes after $b alphabetically"
fi

Output:

apple comes before orange alphabetically

Common String Operations – Quick Reference

Key Takeaways

• Use double quotes for strings when variable values need to appear inside them.
• Use ${#var} to get the string length.
• Use ${var:start:len} to extract a part of the string.
• Use ${var//old/new} to replace all occurrences of a pattern.
• Use ${var^^} and ${var,,} for case conversion.
• Use [[ "$var" == *"pattern"* ]] to check for substring matches.