Using a variable to build a regex

ruby-talk
1

I need to search a roster file (plain text) to match for a player name. I
tried this:

dthacker@buckbeak:~/learning/ruby$ irb
irb(main):001:0> player="S_Avrul"
=> "S_Avrul"
irb(main):002:0> player_line="S_Avrul ger 25 R 1 2 3 7 40 35"
=> "S_Avrul ger 25 R 1 2 3 7 40 35"
irb(main):003:0> re=/player/
=> /player/
irb(main):004:0> re.match(player_line)
=> nil
irb(main):005:0>

How can I use the value of "player" to create the regex?

TIA Dave

2

Dave Thacker wrote:

I need to search a roster file (plain text) to match for a player name. I tried this:

dthacker@buckbeak:~/learning/ruby$ irb
irb(main):001:0> player="S_Avrul"
=> "S_Avrul"
irb(main):002:0> player_line="S_Avrul ger 25 R 1 2 3 7 40 35"
=> "S_Avrul ger 25 R 1 2 3 7 40 35"
irb(main):003:0> re=/player/
=> /player/
irb(main):004:0> re.match(player_line)
=> nil
irb(main):005:0>

How can I use the value of "player" to create the regex?

TIA Dave
  
/#{player}/

···

--
RMagick: http://rmagick.rubyforge.org/

3

In a string literal, "player" would also be the actual string "player"
and not the value of that variable. Do you know how to substitute
inside a string? The same answer applies to Regexp literals in Ruby.

For a hint:
http://phrogz.net/ProgrammingRuby/language.html#substitutions

(In

···

On Dec 22, 8:18 pm, Dave Thacker <dthac...@bluestrain.net> wrote:

dthacker@buckbeak:~/learning/ruby$ irb
irb(main):001:0> player="S_Avrul"
=> "S_Avrul"
irb(main):002:0> player_line="S_Avrul ger 25 R 1 2 3 7 40 35"
=> "S_Avrul ger 25 R 1 2 3 7 40 35"
irb(main):003:0> re=/player/
=> /player/
irb(main):004:0> re.match(player_line)
=> nil
irb(main):005:0>

How can I use the value of "player" to create the regex?

4

You can use #{} substitution in a Regexp, the same way you can in a
string. Thus re=/#{player}/. You can also use Regexp.new to construct
a regexp from a string. (So you can do ordinary string manipulations
to construct the regexp as a string, then turn that into a regexp.)

Both of these will treat any metacharacters in the string as
metacharacters (e.g. A "." in the string will match any character). To
avoid this problem, use Regexp.escape.

--Ken

···

Dave Thacker <dthacker@bluestrain.net> wrote:

I need to search a roster file (plain text) to match for a player name. I
tried this:

dthacker@buckbeak:~/learning/ruby$ irb
irb(main):001:0> player="S_Avrul"
=> "S_Avrul"
irb(main):002:0> player_line="S_Avrul ger 25 R 1 2 3 7 40 35"
=> "S_Avrul ger 25 R 1 2 3 7 40 35"
irb(main):003:0> re=/player/
=> /player/
irb(main):004:0> re.match(player_line)
=> nil
irb(main):005:0>

How can I use the value of "player" to create the regex?

--
Ken (Chanoch) Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/