Shell Programming and Scripting

 $ echo "Every good boy deserves fruit." | grep -iw every

$ echo mortgage | awk '{printf"(?i\\)\\\\b";for(i=1;i<NF;i++) printf ".?[%c%c]",toupper($i),tolower($i); printf "\\\\b\n"}' FS=
(?i\)\\b.?[Mm].?[Oo].?[Rr].?[Tt].?[Gg].?[Aa].?[Gg]\\b

$
$
$ cat -n genperm1.pl
     1  #!/usr/bin/perl
     2  use strict;
     3  use warnings;
     4
     5  sub permute {
     6    my ($x, $y) = @_;
     7    my $len = $#$x;
     8    while ($len >= 0 and $x->[$len] eq '1') { $len-- }
     9    exit if $len < 0;
    10    for (my $i=$#$x; $i>=0; $i--) {
    11      if ($x->[$i] eq '0') {
    12        $x->[$i] = '1';
    13        print map {$x->[$_] eq "0" ? lc $y->[$_] : uc $y->[$_]} 0..$#$x;
    14        print "\n";
    15        bless $x; bless $y;
    16        permute ($x, $y);
    17      } else {
    18        $x->[$i] = '0';
    19      }
    20    }
    21  }
    22
    23  my @arr = split//, lc $ARGV[0];
    24  my @bits = map {0} @arr;
    25  print @arr,"\n";
    26  permute (\@bits, \@arr);
    27
$
$ perl genperm1.pl Linux
linux
linuX
linUx
linUX
liNux
liNuX
liNUx
liNUX
lInux
lInuX
lInUx
lInUX
lINux
lINuX
lINUx
lINUX
Linux
LinuX
LinUx
LinUX
LiNux
LiNuX
LiNUx
LiNUX
LInux
LInuX
LInUx
LInUX
LINux
LINuX
LINUx
LINUX
$
$