How could you add or remove elements in a Hash in Perl?

%FM = ( 'Radio City' => 91.1,
              'Big FM' => 92.7,
              'Red FM' => 93.5,
              'Radio One' => 94.3,
              'Radio Mirchi' => 98.3,
              'Fever' => 104.0,
              'Oye FM' => 104.8,
              'FM Rainbow' => 107.1,
              'FM Gold' => 100.7);

# Add one more element to the hash
$FM{'FM Berhampur'} = 100.6;

# Remove one element from the hash
delete ( $FM{'FM Gold'} );

foreach ( keys %FM )
{
    print "$_ => $FM{$_}\n";
}

How could you find out size of a Hash in Perl?

%FM = ( 'Radio City' => 91.1,
              'Big FM' => 92.7,
              'Red FM' => 93.5,
              'Radio One' => 94.3,
              'Radio Mirchi' => 98.3,
              'Fever' => 104.0,
              'Oye FM' => 104.8,
              'FM Rainbow' => 107.1,
              'FM Gold' => 100.7);

print "size of Hash: ",scalar keys %FM,"\n";
# or
print "size of Hash:  " . keys ( %FM ) . ".\n";

How could you check the existance of a key in a Hash in Perl?

%FM = ( 'Radio City' => 91.1,
              'Big FM' => 92.7,
              'Red FM' => 93.5,
              'Radio One' => 94.3,
              'Radio Mirchi' => 98.3,
              'Fever' => 104.0,
              'Oye FM' => 104.8,
              'FM Rainbow' => 107.1,
              'FM Gold' => 100.7);

if (exists ( $FM { "Fever" } ) )
{
    print "Frequency of FM Fever is $FM{Fever}MHz.\n";
}

How could you list files in a given directory only (ignore subdirectories) in UNIX?

find . -maxdepth 1 -type f  "*.*"

What happens to shell in UNIX, if the ".profile" doesn't exist or gets deleted accidentally?

By default, the ".profile" file doesn't exist in your HOME directory. So, if the file is deleted accidentally or not available, the shell tries to load all defaults from the file "/etc/profile".

What does bless() do?

The process of turning a reference into an object is called 'blessing' and the bless() function
just turns the reference into an object of the required class.

What is the difference between pipe and xargs?

xargs converts the input into command line arguments and is useful when the parameter list is too long for the shell. It splits the parameter list and iterates over the smaller list.

The pipe takes the standard output of the first command and copies it to the standard input. Roughly, pipe is an option to concatenate two/more commands.

What is the substitute to '>/dev/null'?

‘|:’ is built-in pipe-based data sink and faster than ‘>/dev/null’. For instance,

echo "Hello World!" >/dev/null
can be rewritten as
echo "Hello World!" |:

How could you figure out the shell currently being run?

readlink -f /proc/$$/exe

What are the ways to read contents of a file in Perl?

open (FH, "< io.txt") or die $!;
while(<FH>)
{
 print $_;
}
close(FH);

or

use Fcntl;

sysopen(FH, "io.txt", O_RDONLY) or die $!;
while(<FH>)
{
 print $_;
}
close(FH) || die "Couldn't close file properly.";

or

use IO::File;

my $FH = new IO::File("io.txt", "r") or die "could not open $filename : $!\n";
while ($line = $FH->getline())
{
   print $line;
}
$FH->close();