Discovering Perl!

Running Perl programs

To run a Perl program from the Unix command line:

 #perl .pl Perl statements end in a semi-colon:     print "Hello, world";

Double quotes or single quotes may be used around literal strings:

    print "Hello, world";     print 'Hello, world';  However, only double quotes "interpolate" variables and special char-        acters such as newlines ("\n"): You can use parentheses for functions' arguments or omit them according to your personal taste. They are only required occasionally to clarify issues of precedence.            print "Hello, $name\n";     # works fine            print ’Hello, $name\n’;     # prints $name\n literally 

my $os1="Suse 10.1";

my $os2="Tiger 4.*.*.*";

my $no=13;

print"$os1 is far ahead than $os2\n";

print"Squar of $no is ",$no*$no,"\n";

O/P:

[root@station1 perl]# perl perl4.pl

Suse 10.1 is far ahead than Tiger 4.*.*.*

Squar of 13 is 169

my @number = (13,26,39);

print $number[0],"\n";

print $number[1],"\n";

print $number[2],"\n";

O/P:

13

26

39

EG:

my @lang = ("linux","mac","solaris","windows");

print $lang[0],"\n";

print $lang[1],"\n";

print $lang[2],"\n";

print $lang[3],"\n";

O/P:

linux

mac

solaris

windows

EG:

my @info=("Parag",63,"EN-4A");

print $info[0],"\n";

print $info[1],"\n";

print $info[2],"\n";

O/P:

Parag

63

EN-4A

The special variable $#array tells you the index of the last element of an array:

EG:

my @mixed   = ("camel", 42, 1.23);  print $mixed[$#mixed];      

O/P:

[root@station1 perl]# perl perl8.pl

1.23

EG:

my @mixer = ("sam ",13,"mac ",26,"intel ","windows ");

print @mixer[0..5],"\n";

O/P:

[root@station1 perl]# perl perl9.pl

sam 13mac 26intel windows

if

    if ( condition ) {         ...     } elsif ( other condition ) {         ...     } else {         ...     }

There's also a negated version of it:

    unless ( condition ) {         ...     }

This is provided as a more readable version of if (!condition) .

Note that the braces are required in Perl, even if you've only got one line in the block. However, there is a clever way of making your one-line conditional blocks more English like:

    # the traditional way     if ($zippy) {         print "Yow!";     }     # the Perlish post-condition way     print "Yow!" if $zippy;     print "We have no bananas" unless $bananas;

• while

    while ( condition ) {         ...     }

There's also a negated version, for the same reason we have unless :

    until ( condition ) {         ...     }

You can also use while in a post-condition:

    print "LA LA LA\n" while 1;          # loops forever

• for

Exactly like C:

    for ($i=0; $i <= $max; $i++) {         ...     }

The C style for loop is rarely needed in Perl since Perl provides the more friendly list scanning foreach loop.

Perl operators are documented in full in perlop, but here are a few of the most common ones:

• Arithmetic

      +   addition     -   subtraction     *   multiplication     /   division

• Numeric comparison

      ==  equality     !=  inequality     <   less than     >   greater than     <=  less than or equal     >=  greater than or equal

• String comparison

      eq  equality     ne  inequality     lt  less than     gt  greater than     le  less than or equal     ge  greater than or equal