my $string = 'Hallo';
$string =~ tr/al/ex/; # ersetzt a durch e und l durch x

C:\>perl
$string = "abc";

$string =~/abc/xyz/si;
Bareword found where operator expected at - line 3, near "/abc/xyz"
        (Missing operator before yz?)
^Z
syntax error at - line 3, near "/abc/xyz"
Execution of - aborted due to compilation errors.

C:\>

$string =~ s/al/ex/g;

$string = 'Hallo';
$string=~ s/al/ex/g;
print $string; # jetzt ist $string = 'Hexlo' und nicht 'Hexxo'