On page 71 of Pickaxe 2, discussing character classes, it says "The
significance of special regular expression characters (including +) is
turned off inside the brackets."
Why is this a valid regular expression (+ not the first character in
the character class)
%r{^[-+*/]$}
but this isn't? (+ is the first character in the character class)
%r{^[+-*/]$}
--
R. Mark Volkmann
Partner, Object Computing, Inc.
Mark Volkmann wrote:
On page 71 of Pickaxe 2, discussing character classes, it says "The
significance of special regular expression characters (including +) is
turned off inside the brackets."Why is this a valid regular expression (+ not the first character in
the character class)%r{^[-+*/]$}
but this isn't? (+ is the first character in the character class)
%r{^[+-*/]$}
The - character denotes a range in a regexp.
irb(main):001:0> "abc" =~ /[a-c]{3,3}/
=> 0
Putting - at the beginning of the bracket expression makes it literal.
--
vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407
Mark Volkmann said:
Why is this a valid regular expression (+ not the first character in
the character class)%r{^[-+*/]$}
but this isn't? (+ is the first character in the character class)
%r{^[+-*/]$}
Its not the '+' that is getting you ... its the '-'.
Inside brackets, the '-' means a range (e.g. 'A-Z' for the characters A
through Z). But the range "+" (43) through "*" (42) is bad.
Inside brackets, the '-' loses its special meaning when it is the first
(or last) character.
--
-- Jim Weirich jim@weirichhouse.org http://onestepback.org
-----------------------------------------------------------------
"Beware of bugs in the above code; I have only proved it correct,
not tried it." -- Donald Knuth (in a memo to Peter van Emde Boas)
Joel VanderWerf wrote:
The - character denotes a range in a regexp.
Putting - at the beginning of the bracket expression makes it literal.
There's always the all-encompassing (?) backslash escape: /[\-]/,
nikolai
--
Nikolai Weibull: now available free of charge at http://bitwi.se/\!
Born in Chicago, IL USA; currently residing in Gothenburg, Sweden.
main(){printf(&linux["\021%six\012\0"],(linux)["have"]+"fun"-97);}