# Does it contain letters ? ==> '\w'

'Patrick' -match '\w'

# Does it contain digits ? ==> '/d'

'Patrick' -match '\d'

# Find a dot

'patrick.gruenauer@outlook.com' -match '\.'

'patrickgruenauer@outlookcom' -match '\.'

# Does it begin with P ? ==> '^P'

'Patrick' -match '^P'

'Patrick' -match '^a'

# Does it begin with a digit or letter ? Note: use -cmatch instead -match for case-sensitive matches

'Patrick' -cmatch '^[A-Z]'

'Patrick' -cmatch '^[a-z]'

'Patrick' -match '^[0-9]'

# Does it end with a letter ? Note: use -cmatch for case-sensitive matches

'Patrick' -cmatch '[A-Z]$'

'Patrick' -cmatch '[a-z]$'

# Remove German Umlauts

$names = 'Patrick Grünauer', 'Arnold Schwarzenegger', 'Hans Fetisch'

$names -match '[^a-zA-Z ]'

$names -match '[^a-zA-Z ]' -replace 'ü','ue' -replace 'ä','ae' -replace 'ö','oe'

# Remove every second occurence

<# 

^([^.]+.[^.]+)      ==> Create a group (first group is always $1). Capture the first two separated tokens at the start (^).
$1*                 ==> Search for group $1 and replace next character (.) with *
                    Note: [^.] means no dot.

#>

'patrick.gruenauer@outlook.com' -replace '^([^.]+.[^.]+).', '$1*'                   # replace second dot

'patrick.gruenauer@outlook.com' -replace '^([^.]+).', '$1*'                         # replace first dot

'patrick.gruenauer@outlook.com.com' -replace '^([^.]+.[^.]+.[^.]+).', '$1*'         # replace third (last) dot

'patrick.gruenauer@outlook.com.com.' -replace '[.]$', ''                            # replace dot at the end of string

$a = 'patrick.gruenauer@outlook.com.com.'
$b = [regex]::Match($a, '^([^.]+.[^.]+.[^.]+).').value
$b.substring(0,$b.length-1)                                                         # remove everthing after third dot

# Does it end with 2 or 4 letters ? ==> to find e-mail addresses ?
# Source unknown. Thanks to the unknown forum member in a regex forum

'patrick.gruenauer@outlook.com' -match '^[a-zA-Z0-9._-]+@[a-zA-Z0-9._-]+\.[a-zA-Z0-9._-]{2,4}$'    

'patrick.gruenauer@outlook.domain' -match '^[a-zA-Z0-9._-]+@[a-zA-Z0-9._-]+\.[a-zA-Z0-9._-]{2,4}$' 

'patrick.gruenauer@outlookdomain' -match '^[a-zA-Z0-9._-]+@[a-zA-Z0-9._-]+\.[a-zA-Z0-9._-]{2,4}$'