slap

slap (shell clap) - painless argument parsing and dependency check.

Why?

Writing code to parse arguments in a shell scripting language (bash, zsh, fish etc...) is an extremly verbose, repetitive, error prone, and painful process.
This program aims to improve that.

Can't I just use getopt or something similiar?

getopt and similiar tools are not only language-dependent (slap works with a number of shells), but are also just tools to write your own argument parser.
slap is different, in the sense that it puts at your disposal an already written argument parser.
Good luck in writing in bash, powershell, fish or whatever, a full fledged argument parser (using getopt if you want) that takes in consideration things like argument order, possible values, subcommands, argument groups, automatic color-enabled help menus, most similiar argument name suggestions etc.

How?

You declare your CLI in YAML and pass it to slap's stdin and pass all your script's arguments to slap as arguments.
slap makes sure that the arguments you pass to it conform to your YAML description, and if not, it exits with an error code and outputs useful error messages to stderr.
In other words slap handles the argument parsing logic and validation, your script only evalutes the code exported by slap and uses the parsed arguments.
Here is an example bash script:

config="path to your YAML config"
eval "$(slap parse bash -- "$@" <"$config")"

The slap-parse subcommand, if the passed arguments conform to the YAML description, outputs code in the language specified, so you can evaluate it to have access to the variables containing the parsed arguments.
Relax, slap writes to stdout ONLY if the YAML config is valid and the arguments passed conform to it, otherwise it doesn't.

Installation

If you're an Arch Linux user, you can install slap from the AUR:

# This will install a binary named `slap`.
yay -S slap-cli-bin

If you're a Rust programmer, you can install slap with cargo. Make sure to add ~/.cargo/bin to your $PATH.

# This will install a binary named `slap`.
cargo install slap-cli

You can also download a pre-compiled binary (for linux, linux-arm, macos, win-msvc, win-gnu, win32-msvc) from the Releases.

Supported platforms

At the moment slap supports bash, zsh, fish, elvish and powershell.
We are planning to support more shells.
If your favourite shell is not supported, make sure to open an issue.

Completions script generation

Thanks to clap, slap's underlying engine, automatic completions-script generation is supported. For example in bash:

config="path to your YAML config"
slap completions bash <"$config" >completions.bash

completions.bash now contains a bash script that provides command autocompletion for the CLI described in your YAML config file.

Dependency check

If your script depends on some programs you can check if they are in $PATH with the deps subcommand:

slap deps curl jq || exit 1

If curl and jq are found in $PATH the script will continue its execution and nothing will be printed, otherwise an error will be written to stderr and slap will exit with a non-zero exit code.

Absolute path of a script

slap includes a path subcommand that simplifies getting the absolute path of a script:

# before
abs="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"

# with slap
abs="$(slap path -d "${BASH_SOURCE[0]}")"

Both the snippets never dereference symlinks. If you want to dereference symlinks use the -D option.

Demo

Example

Here are two useful bash scripts:

slap deps curl jq || exit 1

eval "$(slap parse bash _ -- "$@" <<-EOF
name: gh-repo-list
version: "1.0"
about: Outputs JSON containing useful informations about your GitHub repos.

settings:
    - ArgRequiredElseHelp
    - ColorAuto

global_settings:
    - ColoredHelp

args:
    - username:
        help: your GitHub username
        required: true
    - password:
        help: your GitHub password
        required: true
    - iterations:
        help: the number of iterations to do. 0 means there is no limit
        long: iterations
        short: i
        default_value: "0"
EOF
)"; [[ -z "${_success}" ]] && exit 1

page=1
while :; do
    data="$(curl -s -X GET \
        -u "${_username_vals}:${_password_vals}" \
    "https://api.github.com/user/repos?page=${page}&per_page100&type=all")"
    len="$(printf '%s\n' "${data}" | jq '. | length')"
    [[ "${_iterations_vals}" == "0" && "${len}" == 0 ]] && break
    printf '%s\n' "${data}"
    [[ "${page}" == "${_iterations_vals}" ]] && break
    page="$((page + 1))"
done

slap deps jq git || exit 1

eval "$(slap parse bash _ -- "$@" <<-EOF
name: gh-clone-repos
version: "1.0"
about: Uses 'gh-repo-list' to clone all your GitHub repos.

settings:
    - ArgRequiredElseHelp
    - ColorAuto

global_settings:
    - ColoredHelp

args:
    - username:
        help: your GitHub username
        required: true
    - password:
        help: your GitHub password
        required: true
    - git_options:
        help: "additional Git options (for example: --git-options '--depth 1')"
        long: git-options
        takes_value: true
        short: o
        allow_hyphen_values: true
EOF
)"; [[ -z "${_success}" ]] && exit 1

for repo in $(gh-repo-list "${_username_vals}" "${_password_vals}" \
    | jq -r "map(.ssh_url) | join(\"\n\")"); do
    if [[ -n "${_git_options_occurs}" ]]; then
        eval "git clone ${_git_options_vals} ${repo}"
    else
        git clone "${repo}"
    fi
done

Learning material

This YAML config probably contains all the options you'll ever need.
For additional informations look at clap's docs.

For powershell, fish, zsh and other examples look here.

Elvish

As of v0.14.1, elvish doesn't support eval yet, so you can use slap to generate elvish code, but you can't yet use the generated code inside an elvish script.
Luckily there is some work going on for this functionality.

Credits

This program is solely made possible by clap, so many thanks to its authors.

License