Perl Regular Expression inconsistency

jkva has asked for the wisdom of the Perl Monks concerning the following question:

Monks,

I noticed that when I match a '{' at the end of a regular expression and use strict and warnings, Perl does not give an error.
I am not sure if this is normal.

jkva

Update : This is perl, v5.8.4 built for i386-linux-thread-multi.

Comment on Perl Regular Expression inconsistency

Replies are listed 'Best First'.
Re: Perl Regular Expression inconsistency by japhy (Canon) on Mar 14, 2006 at 13:31 UTC
The only time '{' needs to be escaped is when it is followed by a set of digits, followed by an optional comma and more digits, followed by a closing '}'. If you don't want that sequence of characters to be interpreted as a quantifier, all you need to do is escape the leading '{'. (This is ignoring places where {...} is part of an escaped expression like `\p{Xyz}` and `\N{CHARACTER}`.) '{' is only a metacharacter in a very specific circumstance. You almost never need to backslash it in a regex. Jeff `japhy` Pinyan, P.L., P.M., P.O.D, X.S.: Perl, regex, and `perl` hacker How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart	[reply] [d/l] [select]
Re: Perl Regular Expression inconsistency by GrandFather (Saint) on Mar 14, 2006 at 11:09 UTC
I see the same behaviour with AS Perl v5.8.7. What is even more interesting is that there is some odd inconsistency in the way different meta characters are handled: `/{/` no error `/}/` no error `/]/` no error `/[/` error `/)/` error `/(/` error DWIM is Perl's answer to Gödel	[reply] [d/l] [select]
Re^2: Perl Regular Expression inconsistency by wazoox (Prior) on Mar 14, 2006 at 11:33 UTC
Well, it doesn't seem that odds to me. `[` starts a range, so it must be escaped; `(` starts a selection, so it must be escaped; `{` doesn't mean anything special, so it hasn't to be escaped.	[reply] [d/l] [select]
Re^3: Perl Regular Expression inconsistency by jkva (Chaplain) on Mar 14, 2006 at 11:44 UTC
Doesn't '{' start a {} quantifier?	[reply]
Re^4: Perl Regular Expression inconsistency by wazoox (Prior) on Mar 14, 2006 at 12:18 UTC
Re^4: Perl Regular Expression inconsistency by sanPerl (Friar) on Mar 14, 2006 at 13:19 UTC
Re^3: Perl Regular Expression inconsistency by GrandFather (Saint) on Mar 14, 2006 at 18:50 UTC
By that logic an unmatched ')' doesn't mean anything so shouldn't need to be escaped, yet it generates an error. japhy's eplanation is satisfying for unmatched '{' and '}' and extends to an unmatched ']' too. Why not extend the argument to an unmatched ')'? Is that so much more likely a "You Really Mean That?" error that it's worth special casing? DWIM is Perl's answer to Gödel	[reply]
Re^4: Perl Regular Expression inconsistency by hv (Prior) on Mar 14, 2006 at 21:00 UTC
Re^4: Perl Regular Expression inconsistency by wazoox (Prior) on Mar 14, 2006 at 21:38 UTC

Back to Seekers of Perl Wisdom