RegEx JavaScript: Match consecutive single line comments

Question

I am trying to write a RegEx to parse groups of single line comments.

Given this input:

//line 1
//line 2
//line 3

//line 4
//line 5
//line 6

I expect to have two matches: Lines 1-3 and 4-6. With my current RegEx (^\/\/[\S\s]+$) I have one match: Lines 1-6, although there is an empty line in between.

The problem is that \s matches any whitespace character, so the blank line is included. But at the same time, line break are part of the RegEx – but only when the line starts with //, so I am stuck.

How can I prevent the RegEx from matching the blank line?

If this can't be done with RegExes, then it's also knowlege :) I am just curious because initially I thought it should be possible — Sven
– Sven, Commented Sep 23, 2017 at 19:15

Jan · Accepted Answer · 2017-09-23 20:12:59Z

2

This is what modifiers are for:

(?:^\/{2}.+\n?)+

With MULTILINE mode, see a demo on regex101.com.

Broken apart, this says:

(?:       # a non-capturing group
    ^     # start of the line
    \/{2} # //
    .+    # anything else in that line
    \n?   # a newline, eventually but greedy
 )+       # repeat the group

answered Sep 23, 2017 at 20:12

Jan

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Carsten Massmann · Accepted Answer · 2017-09-24 06:41:27Z

2

You could try this one:

/(^\/\/[^\n]+$\n)+/gm

see here https://regex101.com/r/CrR9WU/1

This selects first the two / at the beginning of each line then anything that is not a newline and finally (at the end of the line) the newline character itself. There are two matches: rows 1 to 3 and rows 4 to 6. If you also allow "empty comment lines like // then this will do too:

/(^\/\/[^\n]*$\n)+/gm

Edit:
I know, it is a little late now, but Casimir's helpful comment got me on to this modified solution:

/(?:^\/\/.*\n?)+/gm

It solves the problem of the final \n, does not capture groups and is simpler. (And it is pretty similar to Jan's solution ;-) ...)

edited Sep 24, 2017 at 6:41

answered Sep 23, 2017 at 19:18

Carsten Massmann

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2 Comments

Casimir et Hippolyte Over a year ago

You can make more simple if you put the anchor ^ out the group, you don't need the $ anchor. . (the dot) matches all except \n like [^\n]. Also your pattern will fail if a line of comment is at the end of the string without a newline after it or if a comment line doesn't have characters after the slashes: /^\/\/.*(?:\n\/\/.*)*/gm

Carsten Massmann Over a year ago

@Casimir: Thanks for pointing that out! Good alternativa regexp!

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