How to call a function in shell Scripting?

Solution 1:

You don't specify which shell (there are many), so I am assuming Bourne Shell, that is I think your script starts with:

#!/bin/sh

Please remember to tag future questions with the shell type, as this will help the community answer your question.

You need to define your functions before you call them. Using ():

process_install()
{
    echo "Performing process_install() commands, using arguments [${*}]..."
}

process_exit()
{
    echo "Performing process_exit() commands, using arguments [${*}]..."
}

Then you can call your functions, just as if you were calling any command:

if [ "$choice" = "true" ]
then
    process_install foo bar
elif [ "$choice" = "false" ]
then
    process_exit baz qux

You may also wish to check for invalid choices at this juncture...

else
    echo "Invalid choice [${choice}]..."
fi

See it run with three different values of ${choice}.

Good luck!

Solution 2:

#!/bin/bash

process_install()
{
    commands... 
    commands... 
}

process_exit()
{
    commands... 
    commands... 
}


if [ "$choice" = "true" ] then
    process_install
else
    process_exit
fi

Solution 3:

Example of using a function() in bash:

#!/bin/bash
# file.sh: a sample shell script to demonstrate the concept of Bash shell functions
# define usage function
usage(){
    echo "Usage: $0 filename"
    exit 1
}

# define is_file_exists function
# $f -> store argument passed to the script
is_file_exists(){
    local f="$1"
    [[ -f "$f" ]] && return 0 || return 1
}
# invoke  usage
# call usage() function if filename not supplied
[[ $# -eq 0 ]] && usage

# Invoke is_file_exits
if ( is_file_exists "$1" )
then
 echo "File found: $1"
else
 echo "File not found: $1"
fi

Solution 4:

The functions need to be defined before being used. There is no mechanism is sh to pre-declare functions, but a common technique is to do something like:

main() {
  case "$choice" in
    true)  process_install;;
    false) process_exit;;
  esac
}

process_install()
{
  commands...
  commands...
}

process_exit()
{
  commands...
  commands...
}

main()