Passing arguments or parameters to functions

In certain situations, we may need to pass arguments or parameters to functions. In such situations, we can pass arguments as follows.

Calling the script with command-line parameters is as follows:

$ name arg1 arg2 arg3 . . .

Let's type a function as follows:

$  hello() { echo "Hello $1, let us be a friend."; }

Call the function in the command line as follows:

$ hello Ganesh

Output:

Hello Ganesh, let us be a friend

Let's write the script function_07.sh. In this script, we pass command-line parameters to the script as well as the function:

#!/bin/bash
quit()
{
   exit
}
ex()
{
      echo $1 $2 $3
}
ex Hello hi bye# Function ex with three arguments
ex World# Function ex with one argument
echo $1# First argument passed to script
echo $2# Second argument passed to script
echo $3# Third argument passed to script
quit
echo foo

Test the script as follows:

$ chmod +x function_07.sh
$ ./function_07.sh One Two Three

Output:

Hello hi bye
World
One
Two
Three

We can observe from the output that the parameters passed to the function are local to the function. In global scope, the command-line parameters to script are available as $1, $2, $3, and more.

Another example script called function_08.sh to pass multiple arguments to the function is as follows:

#!/bin/bash
countries()
{
# let us store first argument $1 in variable temp
temp=$1
   echo "countries(): \$0 = $0"  # print command
echo "countries(): \$1 = $1"  # print first argument
echo "countries(): total number of args passed = $#"
echo "countries(): all arguments (\$*) passed = -\"$*\""
}

# Call function with one argument
echo "Calling countries() for first time"
countriesUSA

# Call function with three arguments
echo "Calling countries() second time "
countriesUSA India Japan

Test the script as follows:

$ chmod +x function_08.sh
$ ./function_08.sh

Output:

Calling countries() for first time
countries(): $0 = ./hello.sh
countries(): $1 = USA
countries(): total number of args passed = 1
countries(): all arguments ($*) passed = -"USA"
Calling countries() second time
countries(): $0 = ./hello.sh
countries(): $1 = USA
countries(): total number of args passed = 3
countries(): all arguments ($*) passed = -"USA India Japan"

We can create a function that could create a new directory and change to it during the execution of the program. The script function_09.sh is as follows:

#!/bin/bash
# mcd: mkdir + cd; creates a new directory and
# changes into that new directory
mcd ()
{
mkdir $1
cd $1
}
mcd test1

The preceding script will create the test1 folder in the current folder and change the path to the test1 folder.

A common task in many scripts is to ask users to input an answer as either Yes or No. In such situations, the following script function_10.sh would be very useful:

#!/bin/bash
yesno ( )
{
while  true .
do
echo "$*"
echo "Please answer by entering yes or no : "
read reply
case $reply in
yes)
echo "You answered Yes"
return 0
;;
no)
echo "You answered No"
return 1
;;
*  )
echo "Invalid input"
;;
esac
done
}
Yesno

Test the script as follows:

$ chmod +x function_10.sh
$ ./function_10.sh

Output:

Please answer by entering yes or no:
yes
"You answered Yes"
$ ./function_10.sh
Please answer by entering yes or no:
no
"You answered No"

Previous Chapter

9. Working with Functions

Next Chapter

Sharing the data by many functions

Table of Contents for Learning Linux Shell Scripting

Passing arguments or parameters to functions

Table of Contents for
Learning Linux Shell Scripting