Bash functions 

functions in bash used to perform repetitive tasks , we can put all task or command in one function and we can used it by just calling function name.

Creating Functions

syntax

functionName () {
list of commands
}

#!/bin/sh

DisplayMe() {
echo "Hello all"
}

# using function name
DisplayMe

Output

Hello all

Bash function arguments

#!/bin/sh

DisplayMe () {
echo "Hi $1 $2"
}

DisplayMe ken corner

Output

Hi ken corner

Returning Values from Functions

#!/bin/sh

DisplayMe () {
echo "Hi $1 $2"
return 55
}

DisplayMe Ken corner
# Capture value returns by last command
returnValue=$?

echo "Function return value is $returnValue"

Output

Hi ken corner
Function return value is 55

Nested Functions

Nested function is function within function

Example

#!/bin/sh
# Calling one function from another
FunctionOne () {
echo -e "I am in Function One\n"
FunctionTwo
}

FunctionTwo () {
echo "I am in Function Two"
}

# Calling FunctionOne.
FunctionOne

Output

I am in Function One
I am in Function Two

Explanation : in the above example we can see that we only called FunctionOne and then FunctionOne called to FunctionTwo

Bonus Example script of function in bash

In below script we have created some function to get the Total size of RAM, CPU details ,Total core of CPU and Ubuntu Server version, we are using case for menu selection.

Note: In case *) is for value which is not match in case value.

#!/bin/sh

GetRamSize()
{
   TotalRam=$(free -m | grep 'Mem:*' | awk '{print $2}')
   echo " Total RAM size is : $TotalRam MB"
}

GetCPUDetail()
{
   CpuDetailsTMP=$(cat /proc/cpuinfo | grep 'model name' | uniq | awk '{print $4$5$6$7}')
   CpuDetailsNew=$(echo $CpuDetailsTMP | sed -e 's/\//-/g')
   CpuDetails=$(echo $CpuDetailsNew | tr -d ' ')
   echo "CPU is : $CpuDetails"
}

NoOfCoreinCPU()
{
   CpuCore=$(grep -c ^processor /proc/cpuinfo)
   echo "Total No. of Core in CPU : $CpuCore"
}

UbuntuServerVersion()
{
   ServerVersion=$(lsb_release -r --short)
   echo "Ubuntu Server Version : $ServerVersion"
}

echo "
Please Select:

1. Display RAM Size
2. Display CPU detail
3. Display Total Core in CPU
4. Display Version of Ubuntu Server
"
echo "Please Enter Number: "
read GetValue

case $GetValue in
1)
   GetRamSize
;;
2)
   GetCPUDetail
;;
3)
   NoOfCoreinCPU
;; 
4)
   UbuntuServerVersion 
;;
*)
   echo "Sorry you have enter wrong number"
;;
esac