Getting User input

Table of Contents

• User input
• chomp

User input

Let's see how to get input from user

#!/usr/bin/perl
use strict;
use warnings;

# Ask for user input
print 'Enter a number: ';
my $usr_num = <STDIN>;

my $square_num = $usr_num ** 2;
print "Square of entered number is: $square_num\n";

• The input obtained is a string
  • Perl will automatically try to convert to a number as ** is numeric exponentiation operator
  • will be 0 if it cannot be converted to number - we get a helpful warning message(thanks to warnings pragma) that something is probably wrong

$ ./user_input.pl
Enter a number: 23
Square of entered number is: 529

$ ./user_input.pl
Enter a number: abc
Argument "abc\n" isn't numeric in exponentiation (**) at ./user_input.pl line 9, <STDIN> line 1.
Square of entered number is: 0

Note that the warning message printed the user input as "abc\n", meaning our variable has a \n character at the end. While it didn't affect the arithmetic operation(thanks to automatic number conversion), it can be problematic as a string input

#!/usr/bin/perl
use strict;
use warnings;

print "Hi there! What's your name? ";
my $usr_name = <STDIN>;
print 'And your favorite color is? ';
my $usr_color = <STDIN>;

print "\n$usr_name, I like the $usr_color color too :)\n";

and how does the output look like?

$ ./user_input_str.pl 
Hi there! What's your name? learnbyexample
And your favorite color is? blue

learnbyexample
, I like the blue
 color too :)

Further Reading

• perldoc - readline
• perldoc - I/O Operators

chomp

chomp helps to remove trailing input record separator(default is newline) from a string

#!/usr/bin/perl
use strict;
use warnings;

print "Hi there! What's your name? ";
my $usr_name = <STDIN>;
print 'And your favorite color is? ';
my $usr_color = <STDIN>;

# use chomp to remove trailing input record separator
chomp($usr_name);
chomp($usr_color);
print "\n$usr_name, I like the $usr_color color too :)\n";

Now, our output is as desired

$ ./user_input_chomp.pl 
Hi there! What's your name? learnbyexample
And your favorite color is? blue

learnbyexample, I like the blue color too :)

Note that chomp can be combined with variable assignment too: chomp(my $usr_color = <STDIN>)

Further Reading

• perldoc - chomp
• perldoc - input record separator