Brief (Bash) CLI builder

briefcli is a minimal framework to build your command line interfaces for whatever you want.

Example use cases:

• a sysadmin want to give its users a homogeneous CLI to multiple services in its network;
• a developer need to write a CLI tool without rewrite parameters and config file logic.

Features

• Easy command definition interface with only 2 functions usage() that print usage info and call() that execute the real command:

function usage {
    echo 'Print your public ip address.'
}

function call {
    curl "ifconfig.io" # We are not related to ifconfig.io, it's only a simple example.
}

• Parameters can be defined as key=value pairs through:
  • config file
  • environment variables (removing the initial string defaulting to "BC_")
  • command line parameters
  • standard input

Limitations

• No POSIX Argument Syntax Parsing, parameters are only key=value pairs
• No nested subcommands
• No autocompletion

If needed argument parsing or nested subcommand can be managed manually in call() function.

Workflow to build a CLI with briefcli

1. download briefcli
2. create command files
3. set default values in config files
4. deploy briefcli files and create a link with the new CLI name

Download or update briefcli

INSTALL_DIR=/opt # or wherever you want
cd $INSTALL_DIR
git clone https://github.com/fdb-git/briefcli.git
# alternatively you can update with:
git pull

Try briefcli:

cd briefcli
./briefcli print-conf

Configuration

briefcli accept parameter from multiple sources and aggregates them into one associative array that can be used later in command files.

The parameters are read in the following order, in case of homonymy the next one overwrites the previous one:

• config file
• environment variables (only those starting with ENVPREFIX config paramenter)
• command line parameters
• standard input

As an example, a parameter password defined in the config file is not an excellent choice, so it's better to pass it as an environment variable:

BC_user='john' BC_password='123456' ./briefcli print-conf

We can use command line parameters, but for a password also this is not a good choice because the command line is visible in process list:

./briefcli print-conf user='john' password='123456'

The last and more secure for pass secret parameters is via stdin (pay attention to insert newline between parameters):

echo -e "user='john'\npassword='123456'" | ./briefcli print-conf

Finally we can use mixed sources:

echo 'user1=from_stdin' | BC_user2='from_env' ./briefcli print-conf user3='from_parameter'

Create a command files

All commands resides in commands directory and are defined by one file with 2 function inside: call() and help().

To start easily copy the _skel command as new file and start modifing it.

The call() function

It is executed by briefcli on every run and all configuration parameters can be found in the associative array CONF:

function call {
    ${CONF[curl]} "${CONF[endpoint]}/" | ${CONF[w3m]}
}

The help() function

It is used by help command to print user documentation. The CONF array is also available here.

function help {
    echo 'Return a string with usage text'
}

Deploy

Create the link with your CLI name:

ln -s $INSTALL_DIR/briefcli/briefcli /usr/local/bin/mycli

Now if the directory in which the link is contained is included in the path then you can run:

mycli