Using a variable to build a regex

Ruby
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 T. wrote:

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}/

3

On Dec 22, 8:18 pm, Dave T. [email protected] wrote:

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

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

4

Dave T. [email protected] wrote:

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?

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