How to use the command "fish" (with examples)

The “fish” command is an acronym for “The Friendly Interactive SHell”. It is a command-line interpreter designed to be user-friendly and replace traditional shells like bash. Fish offers features such as syntax highlighting, autosuggestions, and helpful error messages.

Use case 1: Start an interactive shell session

Code:

fish

Motivation: Starting an interactive shell session allows you to directly interact with the command line and execute commands.

Explanation: By simply typing “fish” into the terminal, you can start an interactive shell session. This enables you to execute commands and utilize the features provided by the fish shell.

Example output:

Welcome to fish, the friendly interactive shell
Type 'help' for instructions on how to use fish

Use case 2: Start an interactive shell session without loading startup configs

Code:

fish --no-config

Motivation: Sometimes, you may want to start a shell session without loading any startup configurations. This can be useful if you want to troubleshoot issues related to your existing configuration files.

Explanation: The “–no-config” flag tells fish not to load the startup configurations such as aliases, functions, or environment variables. It starts a fresh shell session without any customization.

Example output:

Welcome to fish, the friendly interactive shell
Type 'help' for instructions on how to use fish

Use case 3: Execute specific commands

Code:

fish --command "echo 'fish is executed'"

Motivation: Executing specific commands using the “fish” command can be useful when you want to run a command without entering an interactive shell session.

Explanation: The “–command” flag allows you to specify a command that you want to execute. In this example, the command “echo ‘fish is executed’” will be executed by fish.

Example output:

fish is executed

Use case 4: Execute a specific script

Code:

fish path/to/script.fish

Motivation: You may have a script written in fish syntax that you want to execute. This can be a convenient way to automate tasks or perform complex operations.

Explanation: By providing the path to a specific script file with the “fish” command, fish will execute the script and execute the commands within it.

Example output: (Depends on the script executed)

Use case 5: Check a specific script for syntax errors

Code:

fish --no-execute path/to/script.fish

Motivation: When developing scripts, it’s essential to ensure that there are no syntax errors. This use case allows you to check a script without actually executing it.

Explanation: The “–no-execute” flag instructs fish to check the specified script for syntax errors but not execute it. This is particularly useful for debugging and testing purposes.

Example output: (Depends on the script and if there are any syntax errors)

Use case 6: Execute specific commands from stdin

Code:

echo "echo 'fish is executed'" | fish

Motivation: Using stdin to send commands to fish allows you to execute commands without explicitly typing them in the terminal.

Explanation: In this example, the “echo” command is used to send the desired command “echo ‘fish is executed’” to the fish shell via stdin. Fish will execute the command received from stdin.

Example output:

fish is executed

Use case 7: Start an interactive shell session in private mode

Code:

fish --private

Motivation: Starting an interactive shell session in private mode is useful when you want to ensure that the shell does not access or save any command history.

Explanation: The “–private” flag starts fish in private mode, where the shell does not access any existing command history or save any new command history during the session.

Example output:

Welcome to fish, the friendly interactive shell
Type 'help' for instructions on how to use fish

Use case 8: Define and export an environmental variable that persists across shell restarts (builtin)

Code:

set --universal --export variable_name variable_value

Motivation: Setting an environmental variable that persists across shell restarts can be useful when you want to define a value that is accessible by other processes.

Explanation: The “set” command in fish is used to set the value of a variable. The “–universal” flag makes the variable accessible to other processes, and the “–export” flag exports the variable to the environment.

Example output: (No output when setting a variable)

Conclusion:

The “fish” command provides various use cases for working with the fish shell. Whether you want to start an interactive shell session, execute specific commands or scripts, or configure the shell behavior, the “fish” command offers flexibility and convenience. By understanding each use case and its corresponding arguments, you can effectively utilize the features provided by the fish shell.