Working with function

Some points to be remembered while working with functions,

• Whenever you have a set of commands to be used repetitively in that case defining function for those set of commands can be beneficial
• Function name should be with Lower-case, with underscores to separate words. Separate libraries with ::
• Parentheses are required after the function name.
• The keyword function is optional, but must be used consistently throughout a project.
• If you're writing single functions, use lowercase and separate words with underscore.
• If you're writing a package, separate package names with :: , Braces must be on the same line as the function name and no space between the function name and the parenthesis.
• Function should be used post it has been declared or initialized. If you try to use if before initialization you can expect error as “Command not found”

# # Single function

my_func() {

#Function body

}

## Part of a package

mypackage::my_func() {

#Function body

}

Simple example of function usage,

# cat simple_function.sh

#!/bin/bash

## Single function

my_func()

{

echo "Test Function"

}

## Calling function

my_func

Sample output --

# sh simple_function.sh

Test Function

Using function before its initialization,

# cat simple_function.sh

#!/bin/bash

## Calling function

my_func

## Single function

my_func()

{

echo "Test Function"

}

Sample output --

# sh simple_function.sh

simple_function.sh: line 3: my_func: command not found

Passing arguments to function

# cat simple_function.sh

#!/bin/bash

## Single function

my_func()

{

echo "Inside Function"

echo "arguments received are :"

echo "First=$1, Second=$2 Third=$3, Forth=$4, Fifth=$5, Sixth=$6, Seventh=$7, Eightth=$8 Nineth=$9, Tenth=$10"

}

## Calling function

my_func One Two Three Four Five Six Seven Eight Nine Ten

Sample output –

sh simple_function.sh

Inside Function

arguments received are :

First=One, Second=Two Third=Three, Forth=Four, Fifth=Five, Sixth=Six, Seventh=Seven, Eightth=Eight Nineth=Nine, Tenth=One0

Passing script arguments to function as arguments

cat simple_function.sh

#!/bin/bash

## Single function

my_func()

{

echo "Inside Function"

echo "arguments received are :"

echo "First=$1, Second=$2 Third=$3, Forth=$4, Fifth=$5, Sixth=$6, Seventh=$7, Eightth=$8 Nineth=$9, Tenth=$10"

}

## Calling function

my_func $@

Sample output –

sh simple_function.sh 1 2 3 4 5 6 7

Inside Function

arguments received are :

First=1, Second=2 Third=3, Forth=4, Fifth=5, Sixth=6, Seventh=7, Eightth= Nineth=, Tenth=10

Importing a function defined in another file

cat simple_function

#!/bin/bash

## Single function

my_func()

{

echo "Inside Function"

echo "arguments received are :"

echo "First=$1, Second=$2 Third=$3, Forth=$4, Fifth=$5, Sixth=$6, Seventh=$7, Eightth=$8 Nineth=$9, Tenth=$10"

}

cat calling_function.sh

#!/bin/bash

## importing function file

. simple_function

## Calling function

my_func $@

Sample output –

sh calling_function.sh MY NAME IS JOHN

Inside Function

arguments received are :

First=MY, Second=NAME Third=IS, Forth=JOHN, Fifth=, Sixth=, Seventh=, Eightth= Nineth=, Tenth=MY0