We have already seen in previous chapters that to run any command in the background, we have to terminate the command using &
:
$ command &
Similarly, we can make the function run in the background by appending &
after the function call. This will make the function run in the background so that the terminal will be free:
#!/bin/bash dobackup() { echo "Started backup" tar -zcvf /dev/st0 /home >/dev/null 2>&1 echo "Completed backup" } dobackup & echo -n "Task...done." echo
Test the script as follows:
$ chmod +x function_17.sh $ ./function_17.sh
Output:
Task...done. Started backup Completed backup
Normally, whenever we enter a command, the new process gets created. If we want to make functions from the script to be made available in the current shell, then we need a technique that will run the script in the current shell instead of creating a new shell environment. The solution to this problem is using either the source
or ".
"commands.
The commands source and "." can be used to run the Shell script in the current shell instead of creating a new process. This helps with declaring functions and variables in the current shell.
The syntax is as follows:
$ source filename [arguments]
Or:
$ . filename [arguments]
$ source functions.sh
Or:
$ . functions.sh
If we pass command-line arguments, these will be handled inside a script as $1
, $2
, and more:
$ source functions.sh arg1 arg2
Or:
$ ./path/to/functions.sh arg1 arg2
The source
command does not create a new shell; but runs the Shell scripts in the current shell, so that all the variables and functions will be available in the current shell for usage.