Question

I am trying to find matches in some code using regex.

String I am using

"input[type=radio],input[type=checkbox] {"

To match this I added escape characters for every bracket:

"input\[type=radio\],input\[type=checkbox\] \{"

And I am running .match to find a match in a particular line of code:

"input[type=radio],input[type=checkbox] {".match(/input\[type=radio\],input\[type=checkbox\] \{/)

Which works. But when I turn them into variables, it doesn’t.

str = "input[type=radio],input[type=checkbox] {"
code_to_match_against = "input\[type=radio\],input\[type=checkbox\] \{"

str.match(/#{code_to_match_against}/) # => nil

What am I doing wrong?

Answer 1

The double quotes in here:

code_to_match_against = "input\[type=radio\],input\[type=checkbox\] \{"

are eating your backslashes. Consider this:

>> code_to_match_against = "input\[type=radio\],input\[type=checkbox\] \{"
>> p code_to_match_against
"input[type=radio],input[type=checkbox] {"

So when you interpolate code_to_match_against into your regex, the regex engine thinks you’re using two character classes:

/input[type=radio],input[type=checkbox] {/
#     ^^^^^^^^^^^^      ^^^^^^^^^^^^^^^

and character classes match only one character at a time (unless you append * or +).

Either double your backslashes to get them past the double quotes or use single quotes instead:

>> code_to_match_against = 'input\[type=radio\],input\[type=checkbox\] \{'
>> p code_to_match_against
"input\\[type=radio\\],input\\[type=checkbox\\] \\{"
>> puts code_to_match_against
input\[type=radio\],input\[type=checkbox\] \{