Re: Replacing variable names with values via reference in regexp


Uri Guttman wrote:
"C" == Ceesaxp <ceesaxp@xxxxxxxxx> writes:


C> $var = "variable";
C> $a = 'This is a string with a <%=var%>!'; # single-quoted for no
C> variable substitution
C> $a =~ s/<%=([a-z]+)%>/{ $v=$1; $$v; }/eg;
C> print $a;

that is using eval string

No, it's using symrefs.

and that is very bad.

Well, at least not something to be done lightly.

There is a widely repeated misconception that the /e switch on s/// is
in some way related to eval(STRING). This is wrong. s///ee is related
to eval(STRING) but the single /e just causes the RHS to be treated
like a BLOCK. s///e does not involve runtime compilation any more than
grep {BLOCK} LIST involves runtime compilation.

Indeed I find it helps to think of s///e as the most primative
operation and think of s/// and s///ee in terms of being shorthands for
special cases of s///e.

s/FOO/BAR/e can be thought of as a weird sytax for
do_substitute(qr/FOO/,sub{BAR})

s/FOO/BAR/ is short for s/FOO/ "BAR" /e;
sFOO/BAR/ee is short for for s/FOO/ eval(BAR) /e;

.