Pass action as Parameter on Command Prompt (Linux)

Question

I have written a program in linux bash and following are ways to start/stop that program:

start_program
stop_program
restart_program.

I have copied above scripts in /usr/bin so these scripts are working as command. but I want that instead of above commands I just type program name then pass action as parameter. for example if i want to start program then i should write on command prompt:

ProgramName start

if i want to uninstall then

ProgramName uninstall

if restart

ProgramName restart

so how can i make it that i just write Program name then pass action as parameter and Press enter to do that thing.

Answer 1

A common approach is to use a case statement:

case "$1" in
  start)
    # Your Start Code
    ;;
  stop)
    # Your Stop Code
    ;;
  restart)
    # Your Restart Code
    ;;
  *)
    echo "Usage: $0 {start|stop|restart}" >&2
    exit 1
    ;;
esac

If your restart is just stop then start, you can do:

start() {
  # Your Start Code
}

stop() {
  # Your Stop Code
}

case "$1" in
  start)
    start
    ;;
  stop)
    stop
    ;;
  restart)
    stop
    start
    ;;
  *)
    echo "Usage: $0 {start|stop|restart}" >&2
    exit 1
    ;;
esac

Answer 2

Sionide21 has it right.

There is a great little write up on this over here:

http://wiki.bash-hackers.org/scripting/posparams

Answer 3

Here is an alternative to a case statement.

Start/Stop/restart/uninstall your program with an Argument using if statement in bash/shell.

#!/bin/bash

start_module() {
      # Your start Code
}

stop_module() {
      # Your stop Code
}

restart_module() {
      # Your restart Code
}

uninstall_module() {
      # Your uninstall Code
}


if [ $# != 1 ]; then                # If Argument is not exactly one
    echo "Some message"
    exit 1                         # Exit the program
fi


ARGUMENT=$(echo "$1" | awk '{print tolower($0)}')     # Converts Argument in lower case. This is to make user Argument case independent. 

if   [[ $ARGUMENT == start ]]; then

    start_module

elif [[ $ARGUMENT == stop ]]; then

    stop_module

elif [[ $ARGUMENT == uninstall ]]; then

    uninstall_module

elif [[ $ARGUMENT == restart ]]; then

    restart_module

else 
    echo "Only one valid argument accepted: START | STOP | RESTART | UNINSTALL
          case doesn't matter. "
fi

Save this code into myScript.sh

Usage: 

./myScript.sh Start
./myScript.sh Stop
./myScript.sh check
./myScript.sh uninstall

Here is an example of a real-world program that embodies this style of execution.

Side-Note: Omitting any existing module/functionality or adding another can be done easily.

How to take out/suppress a specific module from running (say for maintenance)?

Taking out a specific module off if statement block will disable it since that module won't be called during runtime.