Powershell - How to replace a number with a variable in a string?

Question

Trying to replace a number (20 with a variable $cntr=120) in a string using replace operator. But getting stuck with $cntr in the output. Where I am doing wrong? Any better solutions please.

Input string

myurl.com/search?project=ABC&startAt=**20**&maxResults=100&expand=log

Desired Output string

myurl.com/search?project=ABC&startAt=**120**&maxResults=100&expand=log

Actual Output string

myurl.com/search?project=ABC&startAt=**$cntr**&maxResults=100&expand=log

Code:

$str='myurl.com/search?project=ABC&startAt=20&maxResults=100&expand=log'
$cntr=120
$str = $str -replace '^(.+&startAt=)(\d+)(&.+)$', '$1$cntr$3'
$str

Answer 1

You need to

• Use double quotes to be able to use string interpolation
• Use the unambiguous backreference syntax , ${n} , where n is the group ID.

In this case, you can use

PS C:\Users\admin> $str='myurl.com/search?project=ABC&startAt=20&maxResults=100&expand=log'
PS C:\Users\admin> $cntr=120
PS C:\Users\admin> $str = $str -replace '^(.+&startAt=)(\d+)(&.+)$', "`${1}$cntr`$3"
PS C:\Users\admin> $str
myurl.com/search?project=ABC&startAt=120&maxResults=100&expand=log

See the .NET regex "Substituting a Numbered Group" documentation :

All digits that follow $ are interpreted as belonging to the number group. If this is not your intent, you can substitute a named group instead. For example, you can use the replacement string ${1}1 instead of $11 to define the replacement string as the value of the first captured group along with the number "1".

Answer 2

A couple things here:

If you just add the "12" you end up with $112$3 which isn't what you want. What I did was appended a slash in front and then removed it on the backend, so the replace becomes $1\12$3.

$str='myurl.com/search?project=ABC&startAt=20&maxResults=100&expand=log'
$cntr=12
$str = ($str -replace '^(.+&startAt=)(\d+)(&.+)$', ('$1\' + $cntr.ToString() +'$3')).Replace("\", "")
$str

Looking to see if there's another way to add the literal "12" in the replace section with the extra character, but this does work.

Here's another way to do it where you have a literal string between the $1 and $3 and then replace that at the end.

$str='myurl.com/search?project=ABC&startAt=20&maxResults=100&expand=log'
$cntr=12
$str = ($str -replace '^(.+&startAt=)(\d+)(&.+)$', ('$1REPLACECOUNTER$3')).Replace("REPLACECOUNTER", "$cntr")
$str