$ cat text_ob.pl
#!/usr/bin/perl -w

use strict;

sub randchar { return  chr int(rand(26)) + 65; }
sub randchar2 { 
        my $t = shift;
        return  chr int(rand(26)) + 65 if $t =~ /[a-zA-Z]/;
        return  int(rand(9)) if $t =~ /\d/;
        return $t;
}

while (<>)
{
   s/(.)/&randchar2($1)/ge;
   print $_;
}

$ ./text_ob.pl < text_ob.pl
#!/VYX/ZEE/AOIV -M

MVV AMGMXL;

YHN DTRQSXDS { GJAHJL  MMY BMO(OLTR(18)) + 70; }
FZJ EVXHJEPY7 { 
        KP $U = RLOFG;
        VCDZBZ  VOD GAU(GHOE(70)) + 67 ZF $F =~ /[E-V|D-K]/;
        RPYZOA  ADX(ERSW(1)) EM $E =~ /\R/;
        GDQIZW $W;
}

VKSXA (<>)
{
   F/(.)/&XDGFXIBL8($8)/QW;
   DTMTE $_;
}
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