User:Swapnil durgade/Perl Notes

Perl Components

Variables

Example

• Define: $message = "Hello World\n";
• Access: print $message;

Array

Example

• Define: @days = ('Mon','Tue','Wed','Thu','Fri','Sat','Sun');
• Access: $days[0]

Hash

Example

• Define: %months = ('January' => 31,'November' => 30,'December' => 31);
• Access: print "Days in November:",$months{'November'},"\n";

Operators

$Sum = 4 + 5

Statements

if

Strings

substr function

Uses

1. get subset of string
2. Replace subset of string with new string.

Syntax

$value = substr($string, $offset, $count);
$value = substr($string, $offset);

substr($string, $offset, $count) = $newstring;
substr($string, $offset, $count, $newstring);  # same as previous
substr($string, $offset)         = $newtail;

E.g.

$string = 'abcd1234';
$subs = substr($string,4);
print $subs;

Output: 1234

$string = 'abcd1234';
substr($string,0,4)="pqrs";
print $string;

Output: pqrs1234

# substitute "at" for "is", restricted to first five characters
substr($string, 0, 5) =~ s/is/at/g;

unpack function

For positioning, use lowercase "x" with a count to skip forward some number of bytes, an uppercase "X" with a count to skip backward some number of bytes, and an "@" to skip to an absolute byte offset within the record.

# extract column with unpack
$a = "To be or not to be";
$b = unpack("x6 A6", $a);  # skip 6, grab 6
print $b;
or not

($b, $c) = unpack("x6 A2 X5 A2", $a); # forward 6, grab 2; backward 5, grab 2
print "$b\n$c\n";
or
be