You could use a do block.

$ perl -le '
> $text = q{this text};
> print do{ $text =~ s{this}{that}; $text };'
that text
$
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I hope this is helpful.

Update: Applying the same principle but using map saves some typing.

$ perl -le '
> $text = q{this text};
> print map { s{this}{that}; $_ } $text;'
that text
$
[download]

As others have pointed out though, your code will be clearer to those who follow if you separate the substitution and the print.