Two types of variables can be used in shell scripting languages: one is the shell variables and the other is the environment variables. The environment variables are worked as the global variables for the scripting languages. The environment-related data that is used to execute the script are stored in the environment variables. These variables are stored based on the key-value pair. The name of the variable is defined by the key that stores the value of the variable. The value of any environment variable can be set or accessed by the Perl script. The methods of accessing and modifying the environment variables using the Perl script are shown in this tutorial.
Uses of the Environment Variables in the Perl Script
The methods of accessing the particular or all environment variables and resetting any environment variable are shown in this part of the tutorial.
Example 1: Print the Particular Environment Variables
The environment variables are stored in the %ENV array that works like the associative array. The variable name is the key of the %ENV array and the value is stored in that particular key. Create a Perl file with the following script that prints three environment variables. The current login username is stored in the $ENV{‘USER’} variable. The current shell value is stored in the $ENV{‘SHELL’} variable. The current working directory is stored in the $ENV{‘PWD’} variable. These three variables are accessed and printed in the script.
use strict;
use warnings;
use 5.34.0;
#Print the values of three environment variables
say "Username is " . $ENV{'USER'};
say "Current shell is " . $ENV{'SHELL'};
say "Current working directory is " . $ENV{'PWD'};
Output:
The following similar output appears after executing the script:
Example 2: Print the First Five Environment Variables
Create a Perl file with the following script to read the first five values of the %ENV array that contains all environment variables. Here, the “foreach” loop is used to read all environment variables based on the sorted key values. The “$counter” variable is used in the script to terminate the loop after printing the five environment variables. The “$counter” variable is incremented in each iteration of the loop and when the value of “$counter” is 5, the “last” statement is executed to exit from the loop.
use strict;
use warnings;
use 5.34.0;
#Initialize the counter
my $counter = 0;
#Iterate the loop to read all environment variables
foreach (sort keys %ENV) {
#Read the name of the environment variable
my $key = $_;
#Read the value of the environment variable
my $value = $ENV{$key};
#Print the variable name with the value
say "$key => $value";
#Increment the counter
$counter++;
#Check the counter value
if ($counter >= 5)
{
#Terminate from the loop
last;
}
}
Output:
The following similar output appears after executing the script:
Example 3: Reset the Environment Variable
In the previous examples, the predefined values of the environment variables are accessed individually and using a loop. However, the value of any environment variable can be changed using the Perl script. Create a Perl file with the following script that prints the location of the HOME, changes the location to “/temp/files”, and prints the location of the HOME again after the update.
use strict;
use warnings;
use 5.34.0;
#Print the value of the particular environment variable
say "The current value of the HOME is " . $ENV{'HOME'};
#Reset the environment variable
$ENV{'HOME'} = '/temp/files';
#Print the value of the particular environment variable after the update
say "The current value of the HOME is " . $ENV{'HOME'};
Output:
The following similar output appears after executing the script:
Example 4: Print the Environment Variables with Formatting
Create a Perl file with the following script that prints the environment variables with formatting using the printf() function. Here, the “foreach” loop is used to read all environment variables like in the previous example. The key-value pair of the environment variable is printed by adding the colon(:) between the key and value, and keeping a space of 15 characters for the key.
use strict;
use warnings;
use 5.34.0;
#Iterate the loop to read all environment variables
foreach my $k (sort keys %ENV) {
#Print the formatted output of the environment variables
printf("%15s : %s\n" , $k, $ENV{$k});
}
Output:
The following similar output appears after executing the script. Some portions at the beginning of the output are shown here:
Conclusion
The environment variables are used for different purposes and it is sometimes required to change the current value of the particular environment variable for any programming purpose. The methods to get and set the values of the environment variables using the Perl script are shown in the examples of this tutorial to help the Perl users.
