$_[0] is aliased to $1. Clearing $1 will therefore clear $_[0], being the same variable. Don't pass globals to functions if that global is going to be modified in the function.

Fix: 

s/(x)/fn "$1"/e;

[download]

This causes a new string to be created from the value of $1.

Update: Note that this isn't usually a problem with Pure Perl subs since @_ is usually only used at the top of the sub.

In reply to Re: Strange modification of @_ by ikegami
in thread Strange modification of @_ by jrw

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