PERL: Basics - 1
In UNIX, the first line of a Perl program should begin with “#!/usr/bin/perl”
and the file should have executable permissions. Then typing the name of the script will cause it to be executed.
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The basic data types known to Perl are scalars($var1), lists(@foo as which is An ordered array of scalars accessed using a numeric subscript), and hashes (%var1 which is An unordered set of key/value pairs accessed using the keys as subscripts) . Some default variables are $_ (The default input and pattern-searching space) , $0 (Program name), $$ (Current process ID), $! (Current value of errno), @ARGV (Array containing command-line arguments for the script), @INC (The array containing the list of places to look for Perl scripts to be evaluated by the do, require, or use constructs), %ENV (The hash containing the current environment), %SIG (The hash used to set signal handlers for various signals) etc...
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The backslash escapes are \n (Newline), \e (Escape), \r (Carriage return), \\ (Backslash), \t (Tab), \” (Double quote), \b (Backspace), \’ (Single quote).
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Scalar $var1 Simple variables that can be a number, a string, or a reference.
A scalar is a “thingy.”
List @var1 An ordered array of scalars accessed using a numeric
subscript. $var1[0]
Hash %var1 An unordered set of key/value pairs accessed using the keys
as subscripts. $var1{key}
Perl uses an internal type called a typeglob to hold an entire symbol table entry. The
effect is that scalars, lists, hashes, and filehandles occupy separate namespaces (i.e.,
$var1[0] is not part of $var1 or of %var1). The prefix of a typeglob is *, to indicate “all
types.” Typeglobs are used in Perl programs to pass data types by reference.
You will find references to literals and variables in the documentation. Literals are
symbols that give an actual value, rather than represent possible values, as do variables.
For example in $var1 = 1, $var1 is a scalar variable and 1 is an integer literal.
Variables have a value of undef before they are defined (assigned). The upshot is that
accessing values of a previously undefined variable will not (necessarily) raise an
exception.
To display, simply use Perl’s print function:
#!/usr/bin/perl
#That should be the first line for any perl script in UNIX
print "C:\\temp"."\n";
#To display the sentencases use print
print "C:/temp"."\n";
#Escape characters like \b, \n, \r, \t etc are similar in perl as well
The basic assignment operator is “=”. The other arithmetic operators work in normal way:
$var1=3;
#variable can be declared using $
$var2=7;
#comments should start with #
$var1++;
#Each command should end with semicolan
--$var2;
#autoincrement and decrement varaible works as as usual
$var3=$var1+$var2;
#Arithmatic variable are also same
$var3=$var1-$var2; #comments can also write at the end of line
$var3=$var1*$var2; #allows single line comments only
$var3=$var1/$var2; #in UNIX should be with .pl extension
$var3=$var1**$var2; #power
$var3=$var1%$var2; #quotient
$var3 += $var2; #Assignments also works as usual
$var4="Hello ";
#string concatenation with .
print "$var4 Hi"."\r";
print $var4 x $var1 ."\n"; # var4 is repeated var1 times
Other logical operators and logical conditions will be same as other languages. Below has syntax with If, unless, until and while loops:
$a=1;
$b=0;
if ($a && $b) {#logical operators are n
print "AND IS NOT WOrkind"."\n"; #Blocks of statements should be in curly braces
} elsif ($a and $b) {
print "AND word IS not working"; #syntaxes are case sensitive
} elsif (!$a || $b) {
print "Negation or OR IS not working";
} elsif (not $a or $b) {
print "OR IS working"."\t";
} elsif (not $a or $b) {
print "OR IS working"."\t";
}
#special variables
print $_.$0.$$.$!."\n"; #default inpout and pattern searching space, program name, process id, current value of error number
#string variables
$s1="Hello";
$s2='Hello';
print $s1."\t".$s2;
$c=9;
$d=0;
unless(--$c==++$d) {#comparison operators are just like we have in arithmetics
print "false statement"; #UNLESS statement
} else {
print "true statement";
}
print "invert if function works" if ($c);
print "invert of unless" unless (!$d);
$e=($c>$d) ? "ternary Operator" : "not working";
print $e;
while($d++ < $c--) { #while loop
print $d."\t".$c."\n";
}
until($a==$b++) { #until loop
print "until loop";
}
