Match lines not starting with first two specific characters

Question

I'm trying to match lines that do not begin with "CD" or any 2-digit number. I've tried:

^[^Cc0-9][^Dd0-9].+?$

but it does not match lines that begin with "Cx" or "0y".

I'm using a program called rxrepl with the above regex as the search string and nothing as the replacement. I'm trying to avoid using grep. Also I can't use parentheses because in rxrepl they are used to capture groups.

Is there a way to avoid using parentheses? They are used for capturing groups in rxrepl. — zcalebz, Jun 14 '16 at 11:30
@PranavCBalan: No, you can't. That will match CD at the beginning of the string or two digits anywhere. The `.+` and `.+?` are also weird and superfluous — Borodin, Jun 14 '16 at 11:38
`^(?:CD|\d{2}).+?$` does the opposite of what I'm trying to achieve. You see in my expression I'm actually trying to match lines not beginning with CD or 2 digit numbers so I can replace them with nothing so that only lines starting with CD and a two digit number remain. — zcalebz, Jun 14 '16 at 11:39
@zcalebz: So why did you write *"I'm trying to match lines in a file beginning with "CD" or any 2-digit number."* — Borodin, Jun 14 '16 at 11:43
@zcalebz: I think my solution below solves your problem. What more do you want? — Borodin, Jun 14 '16 at 11:58

score 3 · Accepted Answer · edited Jun 20 '20 at 09:12

As others have said, you need

^(?:CD|\d\d)

The (?: ... ) is a non-capturing group

Or if you must avoid parentheses of any sort then use

^CD|^\d\d

Update

To comply with your new spec "I'm actually trying to match lines not beginning with CD or 2 digit numbers"

^(?!CD|\d\d)

You need to get over your problem with the parentheses. A negative look-ahead is fine in PCRE and does not capture

score 2 · Answer 2 · answered Jun 14 '16 at 11:27

2

It is either CD or two numbers. So you have to use groups (group1|group2) like this:

^(CD|[0-9]{2})
# ^^ ^^^^^^^^
# |         |   
# either CD |
#           or two digits

answered Jun 14 '16 at 11:27

fedorqui 'SO stop harming'

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Is there a way to avoid using parentheses? They are used for capturing groups in rxrepl. – zcalebz Jun 14 '16 at 11:30
2

You can use a [non-capturing group (?:)](http://stackoverflow.com/q/3512471/1983854). – fedorqui 'SO stop harming' Jun 14 '16 at 11:31

Match lines not starting with first two specific characters

2 Answers2

Update