Let's say I have a string:
$line = "name=""abc"""
I want to extract whatever is written within the quotation marks, like this:
[regex]::Matches($line,'(?<=name=").+?(?=")').Value
This works, but I want the word "name" to be passed as a variable to the regex, i.e. I have a variable $identifyer="name" and I want this to work:
[regex]::Matches($line,'(?<=$identifiyer=").+?(?=")').Value
but it does not work.
It doesn't work because of quoting.
String between single quotes ' are treated as literals.
$identifiyer included.
You'd need to use double quotes " in the regex to have $identifiyer being recognized as variable, but that can be messy.
Luckily it's not the only way to insert values of variables inside strings: String Formatting to the rescue!
$line = 'name="abc"'
$identifier = 'name'
$RegexString = '(?<={0}=").+?(?=")' -f $identifier
[regex]::Matches($line, $RegexString).Value
Much easier to the eye
In my opinion this can be handled more easily by not using regex, but simple string operations. Take a look at below function:
function Get-ValueFromLine {
param(
[string]$Line,
[string]$Key
)
# Split into key and value
$parts = $Line -split '=', 2
if ($parts.Count -ne 2) {
return $null
}
# Trim all double quotes
$lineKey = $parts[0].Trim()
$val = $parts[1].Trim('"')
return $lineKey -eq $Key ? $val : $null
}
Usage
Get-ValueFromLine 'name="abc"' 'name'
"..."strings (double-quoted aka expandable strings) perform string interpolation (expansion of variable values and expressions), not also'...'strings (single-quoted aka verbatim strings). With"..."quoting, if the string value itself contains"chars., escape them as`"or"", or use a double-quoted here-string. See the linked duplicate and the conceptual about_Quoting_Rules help topic.$line -replace "$identifier=`"(.+)`"", '$1'. If you want to rule out false positives and match the line in full:$line -replace "^$identifier=`"(.+)`"`$", '$1'