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March 03, 2025 00:30
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Fish Shell Scripting Cheatsheet

A comprehensive guide to Fish shell scripting, covering syntax, commands, and best practices for efficient shell scripting.

Fish Shell Basics

Core Syntax

Variable Assignment

set variable_name value

Accessing Variables

$variable_name or ${variable_name}

String Concatenation

set combined "$var1 $var2"

Command Substitution

set output (command)

Comments

# This is a comment

Exit Status

echo $status (after command execution)

Control Flow

If Statement

 
if test condition
  # commands
else if test condition
  # commands
else
  # commands
end

For Loop

 
for i in item1 item2 item3
  # commands using $i
end

While Loop

 
while test condition
  # commands
end

Switch Statement

 
switch $variable
  case value1
    # commands
  case value2
    # commands
  case *
    # default commands
end

Functions

Function Definition

 
function function_name
  # commands
end

Calling Functions

function_name arg1 arg2

Function Arguments

$argv[1], $argv[2], etc.

Return Values

Use return value (sets $status variable)

Common Commands & Utilities

File and Directory Operations

Create Directory

mkdir directory_name

Remove Directory

rmdir directory_name (empty directory)
rm -r directory_name (recursive delete)

Create File

touch file_name

Remove File

rm file_name

Copy File

cp source_file destination_file

Move/Rename File

mv source_file destination_file

List Files

ls

Text Manipulation

Print to Console

echo message

Grep (Search)

grep pattern file_name

Sed (Stream Editor)

sed 's/old/new/g' file_name

Awk (Pattern Scanning)

awk '{print $1}' file_name

String Length

string length $variable

Process Management

Run Command in Background

command &

List Running Processes

jobs or ps

Kill Process

kill process_id

Foreground Process

fg job_id

Advanced Fish Scripting

Error Handling

Check Exit Status

if test $status -ne 0

Try…Catch (Simulated)

 
command || echo "Error occurred"

Using command to ignore functions

Forces execution of external command instead of shell function with same name. Useful in scripts.

Signals

Trapping Signals

Fish does not directly support trap. Use external tools or workarounds.

Input and Output Redirection

Redirect Output to File

command > file.txt (overwrite)
command >> file.txt (append)

Redirect Input from File

command < file.txt

Pipe Output

command1 | command2

Redirect Standard Error

command ^ file.txt

Working with Lists

Creating a List

set my_list item1 item2 item3

Accessing List Elements

echo $my_list[1] (first element)

List Length

count $my_list

Iterating Over a List

 
for item in $my_list
  echo $item
end

Configuration and Customization

Configuration Files

Global Configuration

~/.config/fish/config.fish

Functions Directory

~/.config/fish/functions/ (for custom functions)

Autocompletions Directory

~/.config/fish/completions/ (for custom autocompletions)

Custom Functions

Creating a Function

 
function greet
  echo "Hello, $argv[1]!"
end

Making it Persistent

Save the function in ~/.config/fish/functions/greet.fish

Aliases

Creating Aliases (Abbreviations)

 
abbr la 'ls -la'

Making Aliases Persistent

Add abbr commands to ~/.config/fish/config.fish

Autocompletions

Creating Autocompletions

Use complete command to define autocompletions.
Example: complete -c mycommand -f -a "option1 option2"

Custom Completion Files

Store completion definitions in ~/.config/fish/completions/mycommand.fish