Dargs - Dynamic CLI arguments and completion

**

Introduction

Contributions Wanted: If you have use-cases/configurations that could benefit others, please submit them to the examples folder.

What is Dargs?

Dargs is a tool that allows you to define dynamic argument transformations and completions for any CLI command.

Features:

• Use regex to define which CLI argument should be processed
• Use any external command as an argument transformer or completer
• Define cache duration for results

For example, using dargs one can define rules to:

• ssh into an ec2 instance by instance id:

  ssh i-xxxxxxxx

• Run packer build using YAML file format instead of JSON:

  packer build demo.yml

• ssh completions for AWS ec2 instance names:

  ssh ec2:instance_name<tab>

Installation

If you have go

go get -u github.com/aelsabbahy/dargs

If not, download the stand-alone binary

Linux:

curl -L https://github.com/aelsabbahy/dargs/releases/download/v0.0.2/dargs_linux_amd64 -o /usr/local/bin/dargs
chmod +rx /usr/local/bin/dargs

OSX:

curl -L https://github.com/aelsabbahy/dargs/releases/download/v0.0.2/dargs_darwin_amd64 -o /usr/local/bin/dargs
chmod +rx /usr/local/bin/dargs

Completions installation

Bash:

Add the following to your ~/.bashrc

if [[ "$(ls -A ~/.dargs/completions/bash)" ]];then
  for f in ~/.dargs/completions/bash/*;do source "$f";done
fi

Zsh:

Add the following to your ~/.zshrc

if [[ "$(ls -A ~/.dargs/completions/zsh)" ]];then
  for f in ~/.dargs/completions/zsh/*;do source "$f";done
fi

Tutorial

Note: This section walks through the basics of dargs, for more detailed information, see manual

Now that you have dargs installed, lets use dargs to enhance ssh with ec2 abilities and give packer YAML support.

First, create the following ~/.dargs.yml config file:

imports:
  - https://raw.githubusercontent.com/aelsabbahy/dargs/master/examples/quick_start.yml

commands:
  - name: /usr/bin/ssh
    wrapper: ssh
    # Use fzf to fuzzy complete (must have fzf installed)
    #fzf-complete: true
    completers:
      - ec2_name
    transformers:
      - ec2_name # transforms ec2:instance_name -> instance-id (i-xxxxxxxx)
      - ec2_id # Transforms instance-id -> PrivateIpAddress

  - name: /usr/local/bin/packer
    wrapper: packer
    transformers:
      - yaml2json # Converts yaml to json

Lets test out the ec2_id and ec2_name filters using dargs run.

# -n = dry run, only print what would have been executed
$ dargs run -n -- ssh i-05d3e9e370805d0b2
ssh 10.0.0.9

# Same instance but now I'm passing in the instance name
# This was processed by both transformers, try running with `-d` to see what's happening
$ dargs run -n -- ssh ec2:test
ssh 10.0.0.9

# We can pass in the transformers on the command line and run any command with dargs.
# The ~/.dargs.yml config allows us to omit the --transformers, -t flag for commands defined in it
$ dargs run -t ec2_id -- echo i-05d3e9e370805d0b2
10.0.0.9

# Here's an example of the yaml2json filter using cat
$ cat /tmp/test.yml
---
foo: bar
moo: cow

# -v is verbose, prints out the command before executing it
$ dargs run -v -t yaml2json -- cat /tmp/test.yml
cat /tmp/test.json
{
  "foo": "bar",
  "moo": "cow"
}

Typing all that out wouldn't be very efficient. To make this simpler we can either:

alias ssh='dargs run -- ssh'

OR:

$ dargs generate-bins
INFO Wrote /home/***/bin/ssh
INFO Wrote /home/***/bin/packer

# and ensure ~/bin has high precidence in your PATH
$ export PATH=$HOME/bin:$PATH

Lets test out completions

$ dargs generate-completions -f
INFO Wrote /home/***/.dargs/completions/bash/zzdargs_ssh
INFO Wrote /home/***/.dargs/completions/bash/zzdargs_packer

$ source ~/.dargs/completions/bash/*

$ ssh ec2:te<tab>

# We can run the dargs completion command stand-alone to see the results
# syntax: dargs completions -- command prev_arg current_arg
$ dargs completions -- ssh "" "ec2:te"
ec2:test

Manual

Commands

Dargs commands:

• dargs run [flags] -- command command_args..
  • Transforms arguments and runs command.
• dargs generate-bins
  • Generate wrapper bin scripts, alternative to alias cmd='dargs run -- cmd'
• dargs generate-completions [flags]
  • Generate bash/zsh completion scripts
• dargs complete -- cmd prev_arg cur_arg
  • Used by bash/zsh completion scripts, useful for debugging

The dargs config file: ~/.dargs.yml

Note: You can find example dargs config files in the examples folder of this repo.

Dargs configuration consists of four top level keys:

• imports - Import dargs config from file glob or URLs
• transformers - Transform matching CLI args before executing the command
• completers - Complete matching CLI args
• commands - Mapping transformers/completers to commands

# Files to import transformers, completers, and (optionally) commands from
imports:
  # Can be url
  - https://raw.githubusercontent.com/aelsabbahy/dargs/master/examples/quick_start.yml
  # Local path or glob
  - ~/.dargs/config.d/*.yml

# These transform CLI arguments
transformers:
    # Name of transformer
  - name: ec2_id
    # Transformer only runs on CLI args matching this regex
    # Regex groups are available as $RE_0, $RE_1 or if named group $RE_GROUPNAME
    match: '^i-[0-9a-z]+$'
    # (optional) Only match if the previous argument also matches this regex
    # prev-match: '--some-flag'
    # Seconds to cache results (604800 seconds = 1 week)
    cache: 604800
    # Command to run, replacing argument with output of the command
    # To convert an argument into many arguments, use newline as a separator
    # Example:
    # echo -e '-i\n~/.ssh/some_key.pem\n10.11.12.13'
    # Will expand into -i ~/.ssh/some_key.pem 10.11.12.13
    command: |
      aws ec2 describe-instances \
        --filters 'Name=instance-state-name,Values=running' --instance-ids "$RE_0" \
        --query 'Reservations[*].Instances[*].[PrivateIpAddress]' --output text

# These complete CLI arguments
completers:
    # name, match, prev-match, cache have same meaning as transformers
    - name: ec2_name
      match: '^ec2:(?P<name_prefix>.+)$'
      cache: 120
      # Newline separated list of completions
      command: |
      aws ec2 describe-instances \
      --filters "Name=tag:Name,Values=${RE_name_prefix}*" 'Name=instance-state-name,Values=running' \
      --query "Reservations[*].Instances[*].[Tags[?Key=='Name'].Value]" --output text | sed -e "s/^/ec2:/"

commands:
    # Command to match
  - name: /usr/bin/ssh
    # Wrapper name when running `dargs generate-bins`
    wrapper: ssh
    # Use fzf to fuzzy complete (must have fzf installed)
    #fzf-complete: true
    # List of completers/transformers to associate with this command by default
    completers:
      - ec2_name
    # Transformers are run in order which allows them to be chained
    transformers:
      - ec2_id