#!/usr/bin/perl

print "Hello world\n";

# scalar

$myvariable = "hello world";

# array

@myarray = ( "one", "two", "three" );

# hash

%myhash = ( "key1" => "value1", "key2" => "value2" );

#################

# lets get the variables out again

# scalar:

print "my scalar contains: $myvariable \n";

# array

# single item:

print "content of the first position: " . $myarray[0] . "\n";

# traversal:

for ( $i = 0; $i <= $#myarray; $i++ ){
    
    print "item on position: " . $i . " contains: " . $myarray[$i] . "\n";
}

foreach $item ( @myarray ){

    print "the item is: " . $item . "\n";
    
}

# hashes

# single item: 

print "The value belonging to key1, is: " . $myhash{"key1"} . "\n";

# traversal

foreach $key ( keys %myhash ){

    print "here is a value for $key: " . $myhash{$key} . "\n";
}

# lets call a method:

mymethod("here","are","my","argument");


#################################
# methods ( subroutines )

sub mymethod {

    # all the arguments ( parameters )
    # @_

    foreach $argument ( @_ ){
	print "argument: " . $argument . "\n";
    }

}

#################################
#
# running external commands

# 1. system( )

system("ls");

# 2. ``;

@myoutput = `ls`;

# 3. file descriptors

open(LS,"ls |") or die "AAARGH $!\n";
while ( $line = <LS> ){
    # do something with each line
}
close(LS);

################################
#
# Files
# ( > == writing, >> == appending )
# open a file, write lines to it:

open(FILE,">myfile") or die "Fatal: $!\n";

open(FILE2,">>myfile_append") or die "Fatal: $!\n";

print FILE $myvariable . "\n";

print FILE2 $myvariable . "\n";

close(FILE);
close(FILE2);