> perl -le'sub mychop(\$) { chop ${shift()} } print mychop $_ foreach (qw/foo/);'
Modification of a read-only value attempted at -e line 1.
> perl -le'sub mychop(\$) { chop ${$_[0]} } print mychop $_ foreach (qw/foo/);'
Modification of a read-only value attempted at -e line 1.

This is perl, v5.8.0 built for alpha-dec_osf - Compaq Tru64 UNIX V5.1B
This is perl, v5.8.0 built for i386-netbsd - NetBSD 3.0
This is perl, v5.8.6 built for alpha-freebsd - FreeBSD 6.0-RELEASE
This is perl, v5.8.6 built for i386-freebsd-64int - FreeBSD 5.4-RELEASE