combine multiple regex to extract sub string from : separated string

Question

I have been stuck for some time developing a single regex to extract a path from either of the following strings :

1.  "life:living:fast"
2.  "life"
3.  ":life"
4.  ":life:"

I have these regex expressions to use :

(.{3,}):", ":(.{3,}):", ":(.{3,})", "(.{3,})

The first match is all I need. i.e. the desired result for each should be the string located where the word life is. consider life to be a variable

But for some reason combining these individual regex's is a pain: If I excecute them sequentially I get the word 'life' extracted. However I am unable to combine them into one.

I appreciate your effort.

Not very clear what you're asking... can you post some desired input vs output? — Mena
– Mena, Commented Jun 19, 2014 at 10:10
@Mena please see my edit, the desired result for each should be the string located where the word life is. — Bwire
– Bwire, Commented Jun 19, 2014 at 10:13
Still unclear. So you want to find whether "life" is contained within your Strings? Or you want the index of "life"? Or...? — Mena
– Mena, Commented Jun 19, 2014 at 10:15
@Mena consider life to be a place holder or a variable, i.e the string could be *1:*2:*3 or *1 or :*1 or :*1: where *1 is a string that does not contain : — Bwire
– Bwire, Commented Jun 19, 2014 at 10:19
Yes but it's still unclear what you want to do with it. Posting some input vs output might help a great deal here. — Mena
– Mena, Commented Jun 19, 2014 at 10:21

zx81 · Accepted Answer · 2014-06-19 10:25:24Z

2

If you want the first life with the colons, you can use this:

^:?(?:.{3,}?)(?::|$)

See demo

If you prefer the first life without the colons, switch to this:

((?<=^:)|^)([^:]{3,}?)(?=:|$)

See demo

How it Works #1: ^:?(?:.{3,}?)(?::|$)

With ^:?, at the beginning of the string, we match an optional colon
(?:.{3,}?) lazily matches three or more chars up to...
(?::|$) a colon or the end of the string

How it Works #1: ((?<=^:)|^)([^:]{3,}?)(?=:|$)

((?<=^:)|^) ensures that we are either positioned at the beginning of the string, or after a colon immediately after the beginning of the string
([^:]{3,}?) lazily matches chars that are not colons...
up to a point where the lookahead (?=:|$) can assert that what follows is a colon or the end of the string.

edited Jun 19, 2014 at 10:25

answered Jun 19, 2014 at 10:17

zx81

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Comments

Casimir et Hippolyte · Accepted Answer · 2014-06-19 10:28:27Z

2

You can use this pattern, since you are looking for the first word:

(?<=^:?)[^:]{3,}

Note that this pattern doesn't check all the string.

answered Jun 19, 2014 at 10:28

Casimir et Hippolyte

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1 Comment

Bwire Over a year ago

It works too and is precise. but I will stick to zx81's answer as it is broken down to my simple understanding.

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