I'm trying to see if there is an entry for some input in a file, so I'm using a regular expression to query each line:
cat $file | where {$_ -match "^script\$fileName -*"}
where $fileName is some input defined elsewhere.
How do I alter the regex to interpolate the variable instead of matching for '$fileName' ?
In addition to the answer given, as $fileName could contain characters such as '.' or '\' you should escape it as follows:
cat $file | where {$_ -match "^script\\$([regex]::Escape($fileName)) -*"}
The Escape method will escape bits like '.' and '\' for you.
E.g.
[regex]::Escape(".\bar.txt")
gives
\.\\bar\.txt
$fileName gets interpolated so you wind up with a string passed to regex that looks like this:
cat $file | where {$_ -match "^script\foo.txt -*"}
The \ is acting as an escape character for the following character when in fact we want a liternal \ to matched against. In this case, you'll need to escape the escape character e.g.:
cat $file | where {$_ -match "^script\\$fileName -*"}
It is also possible to break the RegEx up inside of powershell.
$fileName = 'test'
'^script\test-*' -match ('\^script\\' + $fileName + '-*')
More readable and will work with multidimensional arrays where variable has brackets []
$fileName = New-Object object[][] 1
$fileName[0] = @('test')
'^script\test-*' -match ('\^script\\' + $fileName[0][0] + '-*')
$. Try leaving out the backslash. If you want to match a literal backslash, add a second backslash instead (to escape the backslash).