Defining new fish commands in a script and parse arguments

Question

Quick question. Is it possible to define new commands by scripting in fish? I want to program a new command along the lines of this:

newFunction --flag1 flag1Input --flag2 flag2Input then space delimited arguments

This new function would only by using already-defined commands in a way that functions do, I just want to be able to pass flags to this new function. Is this possible, or do I have to use another language like Python to create an executable for my hypothetical command?

Answer 1

Sure! Just like in bash (or any interpreted language really) all you need to do is create a file, give it execute permissions and write your fish script in it!

• The first line of the file should be #!/usr/bin/fish (Modify that path if your fish installation is located elsewhere. You can check by calling which fish)
• Start writing your fish script, your arguments will be $argv[1], $argv[2]... etc
• Give your script execute permissions: chmod +x myscript
• Put your script somewhere in your $PATH (for example /usr/local/bin) so that you can call it like other commands in the system.

Here's a useless example script that prints out the arguments you passed:

#!/usr/bin/fish

for i in $argv
        echo $i
end

To parse the arguments you could use the argparse with fish_opt.

What you do is: You specify what your flags are with fish_opt like so:

set -l options (fish_opt -s n -l name --required-val)
set options $options (fish_opt -s h -l help)

where -s is followed by the short form of your flag and -l is followed by the long form.

Then you use argparse to parse your arguments like this:

argparse $options -- $argv

Then you can check on your flags like this:

if set -q _flag_help
    echo "Haalp!"
    return 0
end

Notice that whatever your flag name is, it's gonna be set to a variable of the format _flag_myflag

Here's a complete example:

#!/usr/bin/fish

set -l options (fish_opt -s n -l name --required-val)
set options $options (fish_opt -s h -l help)

argparse $options -- $argv

if set -q _flag_help
    echo "Haalp!"
    exit 0
end

if set -q _flag_name
    echo My name is $_flag_name
    exit 0
end

Now let's call it:

$ myscript
$ myscript --help
Haalp!
$ my_script --name "Anthony"
My name is Anthony