Is [:alnum:] equivalent to [A-Za-z0-9]?

ruby-talk
1

Hi,

I'm trying to creating a regex that will match a string that starts and
ends with an alphanumeric character, and has alphanumeric characters or
dashes in the middle.

This regex gives the expected result:
irb(main):008:0> /^[:alnum:][A-Za-z0-9\-]*[A-Za-z0-9]$/ =~ "apple!"
=> nil
irb(main):009:0> /^[:alnum:][A-Za-z0-9\-]*[A-Za-z0-9]$/ =~ "apple"
=> 0

This regex works as expected on "apple!", but returns nil on "apple":
irb(main):010:0> /^[:alnum:][A-Za-z0-9\-]*[:alnum:]$/ =~ "apple!"
=> nil
irb(main):011:0> /^[:alnum:][A-Za-z0-9\-]*[:alnum:]$/ =~ "apple"
=> nil

Can anyone explain this?

Thanks,
Jeff

2

Jeff wrote:

Hi,

I'm trying to creating a regex that will match a string that starts and
ends with an alphanumeric character, and has alphanumeric characters or
dashes in the middle.

This regex gives the expected result:
irb(main):008:0> /^[:alnum:][A-Za-z0-9\-]*[A-Za-z0-9]$/ =~ "apple!"
=> nil
irb(main):009:0> /^[:alnum:][A-Za-z0-9\-]*[A-Za-z0-9]$/ =~ "apple"
=> 0

This regex works as expected on "apple!", but returns nil on "apple":
irb(main):010:0> /^[:alnum:][A-Za-z0-9\-]*[:alnum:]$/ =~ "apple!"
=> nil
irb(main):011:0> /^[:alnum:][A-Za-z0-9\-]*[:alnum:]$/ =~ "apple"
=> nil

Can anyone explain this?

  Yes, that's a classical mistake: POSIX specifications of this kind
must be included inside other . Try rather

/^[[:alnum:]][A-Za-z0-9\-]*[[:alnum:]]$/

  The way you wrote it just meant ':' or 'a' or 'l' or...

  Vince

···

--
Vincent Fourmond, PhD student
http://vincent.fourmond.neuf.fr/

3

/^[[:alnum:]][A-Za-z0-9\-]*[[:alnum:]]$/

Incidentally, the dash doesn't need to be escaped in the character class
if you put it first:

/^[[:alnum:]][-A-Za-z0-9]*[[:alnum:]]$/

best,
Dan

···

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Posted via http://www.ruby-forum.com/\.

4

VIncent and Daniel,

Thanks very much.

-- Jeff