Beginner's Guide To Travel With Perl - Part 7

Input/Output from user

Let’s see how to take input from user. It can easily be done by . stands for standard input. It can be abbreviated by using simple <>. By declaring a scalar variable and setting it equal to we set the variable equal to whatever will be typed by our user at the command prompt. But here’s a little problem. When we give input in command prompt and press enter, the variable also takes the newline character with the input. As a result an extra newline is printed while printing the value of the variable. To get rid of this problem we can use chomp() function. This function simply removes any erroneous line breaks and spacing from the end of our string.

Look at the following examples to realize this:

Example1:
print "What is your name?";
$name = <>;
print "How old are you?";
$age = <>;
print "Hi $name! You are $age years old.";

Example2:
print "What is your name?";
chomp($name = <>);
print "How old are you?";
chomp($age = <>);
print "Hi $name! You are $age years old.";


File I/O

Let’s go with file now. We can do it simply with Perl. Firstly, see some examples:
Make a file named “input.txt” in the same directory of the code.

input.txt contains:
5
ab
bc
cd
de
ef

Now start our first example:

use strict;
open(my $in, "<", "input.txt") or die "Can't open input.txt: $!"; open(my $out, ">", "output.txt") or die "Can't open output.txt: $!";
my $line = <$in>;
my @lines = <$in>;
for(my $i=0;$i<$line;$i++) { print $out "value is $lines[$i] here\n"; } An output file named “output.txt” will be created.

Another example with same input file:

use strict;
open(my $in, "<", "input.txt") or die "Can't open input.txt: $!"; open(my $out, ">", "output.txt") or die "Can't open output.txt: $!";
my $line = <$in>;
while (<$in>) { # assigns each line in turn to $_
print $out "Just read in this line: $_";
}

An output file named “output.txt” will be created with different output.

Hope all can understand the functionality.
When we're done with our filehandles, we should close() them (though to be honest, Perl will clean up after us if we forget):
close $in or die "$in: $!";


Help Links:

http://www.perl.com/pub/2000/10/begperl1.html
http://perldoc.perl.org/perlintro.html

http://www.perl.org/learn.html
http://learn.perl.org/books.html
http://learn.perl.org/tutorials/
http://www.perl.com/pub/2008/04/23/a-beginners-introduction-to-perl-510.html
http://docstore.mik.ua/orelly/perl2/prog/ch01_05.htm
http://www.tizag.com/perlT/perluserinput.php
http://www.tizag.com/perlT/perlchomp.php

http://perldoc.perl.org/functions/use.html
http://www.well.ox.ac.uk/~johnb/comp/perl/intro.html

http://www.sthomas.net/roberts-perl-tutorial.htm/ch22/use_strict_
http://docstore.mik.ua/orelly/perl/prog3/ch31_19.htm
http://debugger.perl.org/580/perldebtut.html
http://perldoc.perl.org/strict.html


. . . . . To be continued . . . . .