Scalar Variables Hold a single value Partially inspired by shell variables $name = "Ted Reed"; $count = 10;

scalar variables

Asking Perl For Help Perl defaults to being overly permissive We can ask Perl to help us Additional warnings use warnings; Forbid unsafe operations use strict;

Asking Perl For Help

use warnings; Let us know when we've done something suspicious Example file #!/usr/bin/perl use warnings; 2+2; Running the example [guru@station1 ~]$ ./warnings-test.pl Useless use of a constant in void context at warnings-test.pl line 3.

use warnings;

use strict; Forbid potentially unsafe operations The most important restriction is variable declarations Perl variables are global by default, which is unsafe $name = "Dax Kelson"; The better choice is to use lexical variables my $name = "Dax Kelson"; The strict pragma makes undeclared use of globals an error #!/usr/bin/perl use strict; $name = "Dax Kelson"; The example won't run: [sweeks@kweh ~]$ perl strict-test.pl Global symbol "$name" requires explicit package name at strict-test.pl line 3. Execution of strict-test.pl aborted due to compilation errors.

use strict;

Numbers Perl doesn't care, it stores everything the same way internally $count = 255; $count = 0xff; $count = 0b11111111; $count = 2.55e2;

numbers

Strings Perl is built around text Similar interpolation rules to bash $message = 'You won $100'; # no interpolation $message = "$user is over his quota"; # with interpolation

strings

Output With Print The print function prints data to stdout by default print "Hello, world!\n"; # literal string print $message, "\n"; # from a variable

output with print

if The basic control structure if ($size < 10) { print "Not very big\n"; } elsif ($size < 100) { print "Medium sized\n"; } else { print "Very big!\n"; }

if

Conditional Ops Numeric Comparisons < > <= >= == String Comparisons lt gt le ge eq Logical Connectives && || and or

Logical Ops

Getting User Input <> is the "Read from a File Handle" op Used in circumfix my $color = <STDIN>;

getting user input

chomp chomp chomp

chomp

while while while

while

undef undef undef

undef

defined defined defined

defined

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