Bash String Manipulation: Substring, Replace, Split and More

March 17, 2026

Bash String Manipulation: Substring, Replace, Split and More

March 17, 2026

Bash string manipulation uses parameter expansion — a built-in syntax that handles most string operations without any external commands. Understanding ${var#prefix}, ${var//old/new}, and ${var:pos:len} will let you slice, replace, and transform strings entirely within Bash, making your scripts faster and more portable. This guide covers every essential bash string operation with concrete examples.

Operation Syntax Length ${#var} Substring ${var:pos:len} Replace first ${var/old/new} Replace all ${var//old/new} Uppercase ${var^^} Strip prefix ${var#prefix} Strip suffix ${var%suffix}
Quick reference for the most-used bash string manipulation operations

1. String Length and Substring Extraction

bash 
str="Hello, World!"

# String length
echo "${#str}"          # 13

# Substring: start at position 7, take 5 characters
echo "${str:7:5}"       # World

# Start at position 7, take everything to the end
echo "${str:7}"         # World!

# Negative position: start 6 chars from the end
echo "${str: -6}"       # World!   (note the space before -)

# Negative position + length
echo "${str: -6:5}"     # World

# Extract filename without extension
filename="report.tar.gz"
echo "${filename%.*}"   # report.tar  (removes last .gz)
echo "${filename%%.*}"  # report      (removes from first dot)

For negative positions, a space before the minus sign is required: ${str: -6}. Without the space, Bash interprets it as the default-value syntax ${str:-default}.

2. Find and Replace

bash 
str="the cat sat on the mat"

# Replace FIRST occurrence
echo "${str/the/a}"       # a cat sat on the mat

# Replace ALL occurrences (double slash)
echo "${str//the/a}"      # a cat sat on a mat

# Delete a substring (replace with nothing)
echo "${str// /}"         # thecatsatonthemat  (remove all spaces)

# Replace using a glob pattern
path="/usr/local/bin/script.sh"
echo "${path/\/usr\/local/~}"    # ~/bin/script.sh

# Case-insensitive replace requires a workaround (use sed for this)
echo "$str" | sed 's/The/a/gi'   # handles case-insensitive

3. Case Conversion

Bash 4+ supports built-in case conversion operators:

bash 
name="hello world"

echo "${name^^}"    # HELLO WORLD  (all uppercase)
echo "${name,,}"    # hello world  (all lowercase)
echo "${name^}"     # Hello world  (capitalize first char)
echo "${name,}"     # hello world  (lowercase first char)

# Uppercase only certain chars (^[aeiou] = capitalize vowels)
echo "${name^^[aeiou]}"   # hEllO wOrld

4. Stripping Prefixes and Suffixes

The # and % operators strip matched patterns from the start or end of a string. Use one symbol for shortest match, two for longest:

path="/home/user/documents/report.pdf"

# Strip prefix (from the LEFT)
echo "${path#*/}"       # home/user/documents/report.pdf  (strips up to first /)
echo "${path##*/}"      # report.pdf  (strips up to LAST / — greedy)

# Strip suffix (from the RIGHT)
echo "${path%.*}"       # /home/user/documents/report  (strips .pdf)
echo "${path%%.*}"      # /home/user/documents/report  (same here, but watch out with multiple dots)

# Practical: get just the filename
filename="${path##*/}"
echo "$filename"        # report.pdf

# Practical: get directory path
dir="${path%/*}"
echo "$dir"             # /home/user/documents

# Practical: get extension
ext="${filename##*.}"
echo "$ext"             # pdf

5. Splitting Strings

csv="apple,banana,cherry"

# Split on comma using IFS
IFS=',' read -ra parts <<< "$csv"
echo "${parts[0]}"   # apple
echo "${parts[1]}"   # banana
echo "${parts[2]}"   # cherry

# Loop over parts
for part in "${parts[@]}"; do
    echo "Part: $part"
done

# Split a colon-delimited path
IFS=':' read -ra dirs <<< "$PATH"
for dir in "${dirs[@]}"; do
    echo "$dir"
done

6. Trim Whitespace

str="   hello world   "

# Trim with xargs (trims both ends)
trimmed=$(echo "$str" | xargs)
echo "$trimmed"   # hello world

# Trim with parameter expansion (leading spaces)
str="${str#"${str%%[![:space:]]*}"}"

# Trim with sed
trimmed=$(echo "$str" | sed 's/^[[:space:]]*//;s/[[:space:]]*$//')
echo "$trimmed"   # hello world

For bulk find-and-replace across files, the bash sed command guide covers this in depth. For checking whether a string contains a substring, see the bash case statement guide which uses pattern matching.

Summary

Bash parameter expansion handles all common string operations without forking external processes. The key patterns: ${#var} for length, ${var:pos:len} for substrings, ${var//old/new} for global replace, ${var^^}/${var,,} for case, and ${var##*/}/${var%.*} for path/extension manipulation.

More Articles

Continue reading with these related articles:

Pine Script strategy.entry: The Complete Parameter Reference

Pine Script's strategy.entry() is the function you call to open a position in a TradingView strategy. Understanding its parameters —...

March 17, 2026 General

Pine Script plot() Options: Color, Style, Linewidth and More

The plot() function is the primary way to display data on a TradingView chart in Pine Script. Every indicator that...

March 17, 2026 General

Pine Script input() Complete Guide: All Types With Examples

Pine Script's input() functions let you add configurable settings to your indicator or strategy that users can adjust through TradingView's...

March 17, 2026 General

Pine Script for Loop: Syntax, Lookbacks, and Array Iteration

Pine Script's for loop is the primary tool for performing lookback calculations, iterating over arrays, and implementing custom indicators that...

March 17, 2026 General

Pine Script Alerts: The Complete Setup Guide (alertcondition Explained)

Pine Script alerts are what turn an indicator from a passive visual tool into an active notification system. But TradingView's...

March 17, 2026 General

Bash While Loop: Syntax, Examples, and Common Patterns

The bash while loop runs a block of commands repeatedly as long as a condition is true. It's the go-to...

March 17, 2026 Bash

Bash sed Command: Find, Replace, and Edit Files From the Terminal

The bash sed command (stream editor) processes text line by line — finding patterns, replacing content, deleting lines, and inserting...

March 17, 2026 Bash

Bash Read File Line by Line: 5 Methods Explained

Reading a file line by line is one of the most common tasks in Bash scripting, but getting it right...

March 17, 2026 Bash

Bash grep Tutorial: Search, Filter, and Extract Text Like a Pro

Bash grep is one of the most-used command-line tools — it searches file contents for patterns and prints matching lines....

March 17, 2026 Bash

Bash Functions: How to Write, Call, and Return Values

Bash functions let you write reusable blocks of code that can be called with arguments and return results. They're essential...

March 17, 2026 Bash

Bash Exit Codes: What $? Means and How to Use It

Bash exit codes are how processes communicate success or failure to the shell. Every command you run exits with a...

March 17, 2026 Bash

Bash Cron Job Tutorial: Schedule Scripts to Run Automatically

Bash cron jobs are the standard way to schedule scripts to run automatically on Linux and macOS. Whether you need...

March 17, 2026 Bash

Bash Check If File Exists: Complete Guide with Examples

Checking whether a file exists before operating on it is one of the most common bash patterns — and getting...

March 17, 2026 Bash

Bash Array Tutorial: Declare, Access, Loop, and Modify

Bash arrays let you store multiple values in a single variable — essential for processing lists of files, command outputs,...

March 17, 2026 Bash