PowerShell RegExp

Question

I have a string with commas where I want to replace the commas with tildes except where there is a number each side of the comma. Please can someone explain why this works:

$Str = "abc,12345,67,89,xyz,5,f"
$Str -replace '(?<!\d),', '~' -replace ',(?!\d)', '~'

but this does not work:

$Str = "abc,12345,67,89,xyz,5,f"
$Str -replace '(?<!\d),(?!\d)', '~'

Answer 1

You need to use

$Str -replace '(?<!\d),|,(?!\d)', '~'

See the regex demo.

The (?<!\d),(?!\d) regex matches any comma that does not have a digit BOTH on the left AND on the right (so, you would get a match if you had a string like abc,xyd), you need to match any comma that has no digit EITHER on the left OR on the right (so as to find a match in abc,5 and in 5,abc).

The regex details are

• (?<!\d), - a comma that has no digit immediately on the left
• | - or
• ,(?!\d) - a comma that has no digit immediately on the right.