Writing functions

• Write shell function:

name() { 
  command list;
}

• The idea is very simple create a modular scripts.
• Place frequently used commands or logic in a script.
• You can call the function whenever it is required rather writing or repeating the same code again.
• You can create a functions file.
  • /etc/init.d/functions is default functions file which contains functions to be used by most or all shell scripts in the /etc/init.d directory. This file can be autoloaded as and when required.
  • You can view /etc/init.d/functions file with the following command:

less /etc/init.d/functions

• All shell functions are treated as a command.
• You must define a function at the start of a script.
• You must load a function file at the start of a script using source (or .) command:

. /path/to/fuctions.sh

OR

source /path/to/fuctions.sh

• You can call function like normal command:

name
name arg1 arg2

Write a function at the start of a script

A function must be created before calling. For example, the following script (ftest.sh) will fail:

#!/bin/bash
TEST="/tmp/filename"
 
# call delete_file; fail... 
delete_file
 
# write delete_file()
delete_file(){
  echo "Deleting $TEST..."
}

Sample output:

./ftest.sh: line 5: delete_file: command not found

To avoid such problems write a function at the start of a script. Also, define all variables at the start of a script:

#!/bin/bash
# define variables at the start of script 
# so that it can be accessed by our function
TEST="/tmp/filename"
 
# write delete_file() function
delete_file(){
  echo "Deleting $TEST..."
}
 
# call delete_file
delete_file