How to call a function in shell Scripting? - shell

Question

I have a shell script which conditionally calls a function.
For Example:-
if [ "$choice" = "true" ]
then
process_install
elif [ "$choice" = "false" ]
then
process_exit
fi
process_install()
{
commands...
commands...
}
process_exit()
{
commands...
commands...
}
Please let me know how to accomplish this.

Answer 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!

Answer 2

#!/bin/bash
process_install()
{
commands...
commands...
}
process_exit()
{
commands...
commands...
}
if [ "$choice" = "true" ] then
process_install
else
process_exit
fi

Answer 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

Answer 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()

Answer 5

Summary:
Define functions before using them.
Once defined, treat them as commands.
Consider this script, called funcdemo:
#!/bin/bash
[ $# = 0 ] && exhort "write nastygram"
exhort(){
echo "Please, please do not forget to $*"
}
[ $# != 0 ] && exhort "write begging letter"
In use:
$ funcdemo
./funcdemo: line 3: exhort: command not found
$ funcdemo 1
Please, please do not forget to write begging letter
$
Note the potential for a missing function to lie undiscovered for a long time (think 'by a customer at the most critical wrong moment'). It only matters whether the function exists when it is executed, the same as it only matters whether any other command exists when you try to execute it. Indeed, until it goes to execute the command, the shell neither knows nor cares whether it is an external command or a function.

Answer 6

You can create another script file separately for the functions and invoke the script file whenever you want to call the function. This will help you to keep your code clean.
Function Definition : Create a new script file
Function Call : Invoke the script file

Answer 7

#!/bin/bash
# functiontest.sh a sample to call the function in the shell script
choice="true"
function process_install
{
commands...
}
function process_exit
{
commands...
}
function main
{
if [[ "$choice" == "true" ]]; then
process_install
elif [[ "$choice" == "false" ]]; then
process_exit
fi
}
main "$#"
it will start from the main function