Question

I want to know how to match just the 1st character occurrence using regex

Output

    # Address 
cleanse.library.addressDoctor.AddressDoctor.UnlockCode:YR\\FKNT5ST3WCM:\\1J4JTCQQMH/H
cleanse.library.addressDoctor.AddressDoctor.DatabasePath:C:/AddressDoctor
cleanse.library.addressDoctor.AddressDoctor.Optimization:ADDRESSES_SORTED_BY_COUNTRIES
cleanse.library.addressDoctor.AddressDoctor.MemoryMB:600
cleanse.library.addressDoctor.AddressDoctor.CorrectionType:CORRECT_ONLY
cleanse.library.addressDoctor.AddressDoctor.PreLoad.CERTIFIED.PRELOAD_PART:US
cleanse.library.addressDoctor.AddressDoctor.PreLoad.CERTIFIED.PRELOAD_FULL:
cleanse.library.addressDoctor.AddressDoctor.PreLoad.CORRECTION_ONLY.PRELOAD_PART:CA, US
cleanse.library.addressDoctor.AddressDoctor.PreLoad.CORRECTION_ONLY.PRELOAD_FULL:

In this case I want to match just : (the 1st occurrence)

Update

Note: : (1st occurrence in every line)

You can test here

Answer 1

The pattern:

^[^:]*:

matches the start of the input (^), followed by zero or more characters other than : ([^:]*) followed by a :.

So, this matches the first : (and of course everything that precedes the :).

So, let’s say you would like to replace the first : with an @. You then simply group everything that precedes the first :, like this:

^([^:]*):

and replace it with:

$1@

As shown here: http://regexr.com?2v8h8

EDIT

Most regex implementations do not allow a pattern to match the first : in a line. You’d need a variable width look-behind assertion for such a thing, which simply is not supported by most languages.

You could read the file line by line and split on the : and provide a 2nd parameter that indicates the size of the array being returned:

array = line.split(/:/, 2)

Many regex implementation have such a method (I can’t be more specific since I don’t know the language you’re using).