Perl LanguageSpecial variables

Remarks

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Special variables in perl:

1. $_ : The default input and pattern-searching space.

Example 1:

my @array_variable = (1 2 3 4);
foreach (@array_variable){
    print $_."\n";    # $_ will get the value 1,2,3,4 in loop, if no other variable is supplied.
}

Example 2:

while (<FH>){
    chomp($_);    # $_ refers to the iterating lines in the loop.
}

The following functions use $_ as a default argument:

abs, alarm, chomp, chop, chr, chroot, cos, defined, eval,
evalbytes, exp, fc, glob, hex, int, lc, lcfirst, length, log,
lstat, mkdir, oct, ord, pos, print, printf, quotemeta, readlink,
readpipe, ref, require, reverse (in scalar context only), rmdir,
say, sin, split (for its second argument), sqrt, stat, study,
uc, ucfirst, unlink, unpack.

2. @_ : This array contains the arguments passed to subroutine.

Example 1:

example_sub( $test1, $test2, $test3 );

sub example_sub {
    my ( $test1, $test2, $test3 ) = @_; 
}

Within a subroutine the array @_ contains the arguments passed to that subroutine. Inside a subroutine, @_ is the default array for the array operators pop and shift.