skip "#" regular expression Javascript

Question

I would like to skip the comments using javascript. I can only get the reverse, meaning not skipping the comments. The following syntax:

#GSM settings\r\n   <----- Skip these
Apn internet\r\n
Pass \r\n
User \r\n
Pin \r\n
Dial *99#\r\n
KeepAlive 0\r\n
#ETH TEST\r\n                  <---- skip
Mac 00:60:37:12:34:56\r\n
EthIpv4 192.168.0.10\r\n
Subnet 255.255.255.0\r\n
Gwip 192.168.0.1\r\n
Autoip 0\r\n

You can replace comments with an empty string, thus removing them, like so: string.replace(/#[^\n]*/g, '') or equivalent. — caiosm1005
– caiosm1005, Commented Jan 23, 2013 at 8:07

stema · Accepted Answer · 2013-01-23 08:17:50Z

1

I am not sure I understood 100%, if you want to match rows that are not starting with a "#", you can do it like this:

/^(?!#).*/

This matches only if after the start of the string there is not "#" directly following.

See it here at Regexr

(?!#) is a negative lookahead assertion, that fails if there is a "#" following this position. Since it is after the ^ anchor, the whole expression will fail, if the first character is a "#".

If there can be whitespaces before the "#", you can add them like this:

/^(?!\s*#).*/

See it here on Regexr

edited Jan 23, 2013 at 8:17

answered Jan 23, 2013 at 8:11

stema

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7 Comments

Christoph Over a year ago

perhaps for safety's sake include whitespaces in front of the hash or omit the ^.

nhahtdh Over a year ago

Actually, the "not" part can be done outside with ! operator. No need for a look-around or matching the rest of the string.

nikolas Over a year ago

how does the multiline /m affect the output?

Christoph Over a year ago

@nikolas /^(?!\s*#).*\r\n/gm is the complicated version of stema's one without m parameter. If you specify this param, you need to stop at the linebreak, without you don't.

Christoph Over a year ago

@nhahtdh mind to provide a regex for that? I never heard of a negative operator other than negative lookarounds or negative character classes.

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