Regexp help

Ruby
1

K, so I suck at regular expressions. I just don’t seem to understand
them.

What I want to do is determine if a string includes 2 special characters
a semi-colon and a question mark.

Here’s my example that I’m trying to work with.

irb(main):009:0> encoding = “;6277200301500269=?”
=> “;6277200301500269=?”
irb(main):010:0> encoding.include?(%r{;?}.to_s)
=> false
irb(main):011:0>

I want this to return true, but it doesn’t

Can anyone help me out?

thanks,

~Jeremy

2

Jeremy W. wrote:

What I want to do is determine if a string includes 2 special characters
a semi-colon and a question mark.

You don’t need regular expressions to do that, try this instead:

irb> encoding.include? “;” and encoding.include? “?”
=> true

On the other hand, if you want to use regular expressions regardless,
you should notice that String#include? takes a string rather than a
Regexp.

Note that:
irb> %r{;?}.to_s

“(?-mix:;\?)”

So
encoding.include?(%r{;?}.to_s)

is equivalent to
encoding.include?("(?-mix:;\?)")

which is not going to succeed.

To use a regexp, try:
irb> encoding =~ /(;.?)|(?.;)/
=> true.

best
Dan

3

On Sep 18, 4:04 pm, Jeremy W. [email protected] wrote:

On the other hand, if you want to use regular expressions regardless,
is equivalent to

irb(main):004:0>

So what does the 0 mean? 0 matches? If all else fails, I will use the
ugly version :slight_smile:

It means that it found the first match starting at index 0 in the
string. (Try reading the documentation on the =~ method.)

Note that the supplied regexp will fail if your string has a newline
in it. You may want to append the ‘m’ (multiline) modifier to it, e.g.
/;.?|?.;/m
(There’s also no need for the parentheses, and a minor theoretical
speed/memory reason to leave them off.)

4

Daniel L. wrote:

Jeremy W. wrote:

What I want to do is determine if a string includes 2 special characters
a semi-colon and a question mark.

You don’t need regular expressions to do that, try this instead:

irb> encoding.include? “;” and encoding.include? “?”
=> true

On the other hand, if you want to use regular expressions regardless,
you should notice that String#include? takes a string rather than a
Regexp.

Note that:
irb> %r{;?}.to_s

“(?-mix:;\?)”

So
encoding.include?(%r{;?}.to_s)

is equivalent to
encoding.include?("(?-mix:;\?)")

which is not going to succeed.

To use a regexp, try:
irb> encoding =~ /(;.?)|(?.;)/
=> true.

best
Dan

Thanks for the help. I would like to use a regexp becuase I think it
will look nicer in the code. I tried your example and got

C:\rails_apps\hotswipe>irb
irb(main):001:0> require ‘config/environment’
=> true
irb(main):002:0> encoding = “;6277200301500269=?”
=> “;6277200301500269=?”
irb(main):003:0> encoding =~ /(;.?)|(?.;)/
=> 0
irb(main):004:0>

So what does the 0 mean? 0 matches? If all else fails, I will use the
ugly version :slight_smile:

thanks,
~Jeremy

5

Gavin K. wrote:

It means that it found the first match starting at index 0 in the
string. (Try reading the documentation on the =~ method.)

ok, that makes sense. I did check out the docs on
http://www.ruby-doc.org/core/
I clicked the =~ method under Regexp and it sends me to
rxp.match(str) => matchdata or nil
Returns a MatchData object describing the match, or nil if there was no
match. This is equivalent to retrieving the value of the special
variable $~ following a normal match.

which didn’t say anything about indexes. Are there any other sites that
have different documentation?

~Jeremy

6

Jeremy W. wrote:

Gavin K. wrote:

It means that it found the first match starting at index 0 in the
string. (Try reading the documentation on the =~ method.)

ok, that makes sense. I did check out the docs on
RDoc Documentation
I clicked the =~ method under Regexp and it sends me to
rxp.match(str) => matchdata or nil
Returns a MatchData object describing the match, or nil if there was no
match. This is equivalent to retrieving the value of the special
variable $~ following a normal match.

which didn’t say anything about indexes. Are there any other sites that
have different documentation?

~Jeremy

haha, ok you can disregard that, I looked under string and seen what you
were talking about. My bad.

thanks

~Jeremy

7

From: Jeremy W. [mailto:[email protected]]

What I want to do is determine if a string includes 2 special

characters a semi-colon and a question mark.

irb(main):009:0> encoding = “;6277200301500269=?”

=> “;6277200301500269=?”

irb(main):010:0> encoding.include?(%r{;?}.to_s)

=> false

start simple,

check if a string contains a ; or ?

irb(main):095:0> encoding[/;|?/]
=> “;”

check if a string starts w a ; and ends with a ?

irb(main):096:0> encoding[/^;.*?$/]
=> “;6277200301500269=?”

string[regex] returns the matched (sub)string (wc is true in ruby)
otherwise it returns nil (wc is false in ruby)

kind regards -botp

8

If it’s going to be going heavy on the regexp… (I have no shame)

Try TextualRegexp. Seriously, it was written so you DON"T have to
hurt your brain over it.

~ Ari
English is like a pseudo-random number generator - there are a
bajillion rules to it, but nobody cares.