Bash

Shell scripting commands for automation, text processing, conditionals, loops, and writing maintainable Bash scripts.

100 commands

Browse by Topic

Getting Started

Quick setup and installation

3commands

Scripting

Script basics

15commands

Variables

Variable operations

14commands

Loops

Loop constructs

11commands

Functions

Function definitions

8commands

Arrays

Array operations

14commands

Strings

String manipulation

14commands

Conditionals

Conditional logic

21commands

Check Bash version

$ bash --version

Display the current Bash shell version information

Install latest Bash (macOS)

$ brew install bash

Install the latest version of Bash using Homebrew on macOS

Check current shell

$ echo $SHELL

Display the path of the current default login shell

Shebang line

$ #!/bin/bash

Standard bash script header.

Make executable

$ chmod +x script.sh

Make script executable.

Debug mode

$ bash -x script.sh

Run script in debug mode.

Exit on error

$ set -e

Exit immediately if command fails.

Error on undefined vars

$ set -u

Error on undefined variables.

Pipe fail mode

$ set -o pipefail

Fail on pipe errors.

Strict mode

$ set -euo pipefail

Enable all safety options.

Debug with line numbers

$ PS4='+${BASH_SOURCE}:${LINENO}: ' bash -x script.sh

Debug with source file and line info.

Syntax check only

$ bash -n script.sh

Check syntax without executing.

Get script directory

$ DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"

Get absolute path of script directory.

Source another script

$ source ./lib.sh

Include another script file.

Exit trap

$ trap 'cleanup' EXIT

Run cleanup function on exit.

Error trap

$ trap 'echo "Error on line $LINENO"' ERR

Handle errors with line number.

Signal trap

$ trap 'echo Interrupted; exit 1' INT TERM

Handle interrupt and terminate signals.

Remove trap

$ trap - EXIT

Remove a previously set trap.

Set variable

$ VAR="value"

Assign value to variable.

Export variable

$ export VAR="value"

Export variable to environment.

Default value

$ echo ${VAR:-default}

Use default if variable unset.

Assign default

$ echo ${VAR:=default}

Assign default if unset and return it.

Error if unset

$ echo ${VAR:?"error message"}

Error if variable unset.

Read-only variable

$ readonly VAR="value"

Create read-only variable.

Unset variable

$ unset VAR

Remove variable definition.

Command substitution

$ result=$(command)

Capture command output in variable.

Arithmetic expansion

$ result=$((a + b))

Perform arithmetic calculation.

Positional parameters

$ echo "$1 $2 $@"

Access script arguments.

Number of arguments

$ echo $#

Get number of positional parameters.

Last exit status

$ echo $?

Get exit status of last command.

Current PID

$ echo $$

Get process ID of current shell.

Background PID

$ echo $!

Get PID of last background job.

Range loop

$ for i in {1..10}; do echo $i; done

Loop through number range.

C-style for loop

$ for ((i=0; i<10; i++)); do echo $i; done

Loop with counter variable.

File loop

$ for f in *.txt; do echo "$f"; done

Loop through files.

Read file lines

$ while IFS= read -r line; do echo "$line"; done < file

Loop through file lines safely.

Infinite loop

$ while true; do sleep 1; done

Run infinite loop.

Until loop

$ until [ -f file.txt ]; do sleep 1; done

Loop until condition is true.

Loop with index

$ for i in "${!arr[@]}"; do echo "$i: ${arr[$i]}"; done

Loop with array indices.

Break loop

$ for i in {1..10}; do [ $i -eq 5 ] && break; echo $i; done

Exit loop early with break.

Continue loop

$ for i in {1..5}; do [ $i -eq 3 ] && continue; echo $i; done

Skip iteration with continue.

Process substitution

$ while read -r line; do echo "$line"; done < <(command)

Read from command output.

Loop with step

$ for i in {0..20..5}; do echo $i; done

Loop with custom step value.

Define function

$ function name() { echo "Hello"; }

Define a function.

Function shorthand

$ name() { echo "Hello"; }

Define function without keyword.

Function with args

$ greet() { echo "Hello, $1"; }

Function with positional arguments.

Local variable

$ func() { local var="value"; echo $var; }

Declare local variable in function.

Return value

$ func() { return 0; }

Return exit status from function.

Capture function output

$ result=$(function_name arg1 arg2)

Capture function output to variable.

All function args

$ func() { for arg in "$@"; do echo "$arg"; done; }

Iterate over all function arguments.

Check function exists

$ declare -f function_name > /dev/null && function_name

Call function only if it exists.

Declare array

$ arr=(one two three)

Create indexed array.

Access element

$ echo "${arr[0]}"

Get element by index.

All elements

$ echo "${arr[@]}"

Get all array elements.

Array length

$ echo "${#arr[@]}"

Get number of elements.

Array indices

$ echo "${!arr[@]}"

Get all array indices.

Append to array

$ arr+=(four)

Add element to end of array.

Array slice

$ echo "${arr[@]:1:2}"

Get subset of array (offset:length).

Delete element

$ unset 'arr[1]'

Remove element at index.

Associative array

$ declare -A hash; hash[key]="value"

Create key-value associative array.

Associative keys

$ echo "${!hash[@]}"

Get all keys of associative array.

Array from command

$ arr=($(ls *.txt))

Populate array from command output.

Safe array from lines

$ mapfile -t arr < file.txt

Read file lines into array safely.

Join array

$ IFS=','; echo "${arr[*]}"

Join array elements with delimiter.

Last element

$ echo "${arr[-1]}"

Get last array element (Bash 4.2+).

String length

$ echo "${#str}"

Get length of string.

Substring

$ echo "${str:0:5}"

Extract substring (offset:length).

Substring from end

$ echo "${str: -3}"

Get last N characters.

Replace first

$ echo "${str/find/replace}"

Replace first occurrence.

Replace all

$ echo "${str//find/replace}"

Replace all occurrences.

Remove prefix

$ echo "${str#prefix}"

Remove shortest prefix match.

Remove prefix greedy

$ echo "${str##*/}"

Remove longest prefix (basename).

Remove suffix

$ echo "${str%suffix}"

Remove shortest suffix match.

Remove suffix greedy

$ echo "${str%%.*}"

Remove longest suffix (remove extension).

Uppercase

$ echo "${str^^}"

Convert to uppercase (Bash 4+).

Lowercase

$ echo "${str,,}"

Convert to lowercase (Bash 4+).

Capitalize first

$ echo "${str^}"

Capitalize first character (Bash 4+).

Replace at start

$ echo "${str/#old/new}"

Replace if at beginning.

Replace at end

$ echo "${str/%old/new}"

Replace if at end.

Discussion

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Bash

Shell scripting commands for automation, text processing, conditionals, loops, and writing maintainable Bash scripts.

100 commands

Browse by Topic

Getting Started

Quick setup and installation

3commands

Scripting

Script basics

15commands

Variables

Variable operations

14commands

Loops

Loop constructs

11commands

Functions

Function definitions

8commands

Arrays

Array operations

14commands

Strings

String manipulation

14commands

Conditionals

Conditional logic

21commands

Check Bash version

$ bash --version

Display the current Bash shell version information

Install latest Bash (macOS)

$ brew install bash

Install the latest version of Bash using Homebrew on macOS

Check current shell

$ echo $SHELL

Display the path of the current default login shell

Shebang line

$ #!/bin/bash

Standard bash script header.

Make executable

$ chmod +x script.sh

Make script executable.

Debug mode

$ bash -x script.sh

Run script in debug mode.

Exit on error

$ set -e

Exit immediately if command fails.

Error on undefined vars

$ set -u

Error on undefined variables.

Pipe fail mode

$ set -o pipefail

Fail on pipe errors.

Strict mode

$ set -euo pipefail

Enable all safety options.

Debug with line numbers

$ PS4='+${BASH_SOURCE}:${LINENO}: ' bash -x script.sh

Debug with source file and line info.

Syntax check only

$ bash -n script.sh

Check syntax without executing.

Get script directory

$ DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"

Get absolute path of script directory.

Source another script

$ source ./lib.sh

Include another script file.

Exit trap

$ trap 'cleanup' EXIT

Run cleanup function on exit.

Error trap

$ trap 'echo "Error on line $LINENO"' ERR

Handle errors with line number.

Signal trap

$ trap 'echo Interrupted; exit 1' INT TERM

Handle interrupt and terminate signals.

Remove trap

$ trap - EXIT

Remove a previously set trap.

Set variable

$ VAR="value"

Assign value to variable.

Export variable

$ export VAR="value"

Export variable to environment.

Default value

$ echo ${VAR:-default}

Use default if variable unset.

Assign default

$ echo ${VAR:=default}

Assign default if unset and return it.

Error if unset

$ echo ${VAR:?"error message"}

Error if variable unset.

Read-only variable

$ readonly VAR="value"

Create read-only variable.

Unset variable

$ unset VAR

Remove variable definition.

Command substitution

$ result=$(command)

Capture command output in variable.

Arithmetic expansion

$ result=$((a + b))

Perform arithmetic calculation.

Positional parameters

$ echo "$1 $2 $@"

Access script arguments.

Number of arguments

$ echo $#

Get number of positional parameters.

Last exit status

$ echo $?

Get exit status of last command.

Current PID

$ echo $$

Get process ID of current shell.

Background PID

$ echo $!

Get PID of last background job.

Range loop

$ for i in {1..10}; do echo $i; done

Loop through number range.

C-style for loop

$ for ((i=0; i<10; i++)); do echo $i; done

Loop with counter variable.

File loop

$ for f in *.txt; do echo "$f"; done

Loop through files.

Read file lines

$ while IFS= read -r line; do echo "$line"; done < file

Loop through file lines safely.

Infinite loop

$ while true; do sleep 1; done

Run infinite loop.

Until loop

$ until [ -f file.txt ]; do sleep 1; done

Loop until condition is true.

Loop with index

$ for i in "${!arr[@]}"; do echo "$i: ${arr[$i]}"; done

Loop with array indices.

Break loop

$ for i in {1..10}; do [ $i -eq 5 ] && break; echo $i; done

Exit loop early with break.

Continue loop

$ for i in {1..5}; do [ $i -eq 3 ] && continue; echo $i; done

Skip iteration with continue.

Process substitution

$ while read -r line; do echo "$line"; done < <(command)

Read from command output.

Loop with step

$ for i in {0..20..5}; do echo $i; done

Loop with custom step value.

Define function

$ function name() { echo "Hello"; }

Define a function.

Function shorthand

$ name() { echo "Hello"; }

Define function without keyword.

Function with args

$ greet() { echo "Hello, $1"; }

Function with positional arguments.

Local variable

$ func() { local var="value"; echo $var; }

Declare local variable in function.

Return value

$ func() { return 0; }

Return exit status from function.

Capture function output

$ result=$(function_name arg1 arg2)

Capture function output to variable.

All function args

$ func() { for arg in "$@"; do echo "$arg"; done; }

Iterate over all function arguments.

Check function exists

$ declare -f function_name > /dev/null && function_name

Call function only if it exists.

Declare array

$ arr=(one two three)

Create indexed array.

Access element

$ echo "${arr[0]}"

Get element by index.

All elements

$ echo "${arr[@]}"

Get all array elements.

Array length

$ echo "${#arr[@]}"

Get number of elements.

Array indices

$ echo "${!arr[@]}"

Get all array indices.

Append to array

$ arr+=(four)

Add element to end of array.

Array slice

$ echo "${arr[@]:1:2}"

Get subset of array (offset:length).

Delete element

$ unset 'arr[1]'

Remove element at index.

Associative array

$ declare -A hash; hash[key]="value"

Create key-value associative array.

Associative keys

$ echo "${!hash[@]}"

Get all keys of associative array.

Array from command

$ arr=($(ls *.txt))

Populate array from command output.

Safe array from lines

$ mapfile -t arr < file.txt

Read file lines into array safely.

Join array

$ IFS=','; echo "${arr[*]}"

Join array elements with delimiter.

Last element

$ echo "${arr[-1]}"

Get last array element (Bash 4.2+).

String length

$ echo "${#str}"

Get length of string.

Substring

$ echo "${str:0:5}"

Extract substring (offset:length).

Substring from end

$ echo "${str: -3}"

Get last N characters.

Replace first

$ echo "${str/find/replace}"

Replace first occurrence.

Replace all

$ echo "${str//find/replace}"

Replace all occurrences.

Remove prefix

$ echo "${str#prefix}"

Remove shortest prefix match.

Remove prefix greedy

$ echo "${str##*/}"

Remove longest prefix (basename).

Remove suffix

$ echo "${str%suffix}"

Remove shortest suffix match.

Remove suffix greedy

$ echo "${str%%.*}"

Remove longest suffix (remove extension).

Uppercase

$ echo "${str^^}"

Convert to uppercase (Bash 4+).

Lowercase

$ echo "${str,,}"

Convert to lowercase (Bash 4+).

Capitalize first

$ echo "${str^}"

Capitalize first character (Bash 4+).

Replace at start

$ echo "${str/#old/new}"

Replace if at beginning.

Replace at end

$ echo "${str/%old/new}"

Replace if at end.

Discussion

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