How to use the PowerShell match operator

Question

Version: PowerShell 2.0

I have the following:

$pattern = '^.\d_\d\d\d\d\d\d\d\d_\d\d\d\d\d\d\d\d\d\d\d\d\d\d.pdf$'
$filename = '123456_12345678_12345678901234.pdf'
$filename -match $pattern

I want the ^ and $ characters to start and end the string. Since I'm using the wild card '.' in the beginning, I really just care about the $ terminator. These characters do not appear to work as I expect in PowerShell because the above code returns FALSE.

What pattern will return true for $goodname, but false for $badname. The number of digits in the first segment of the name is unknown.

$goodname = '123456_12345678_12345678901234.pdf'
$badname = '123456_12345678_12345678901234.pdf.hold'

Answer 1

It returns false because the filename does not match the pattern.

A better regex would be:

$pattern = '^\d+_\d{8}_\d{14}\.pdf$'
$filename = '123456_12345678_12345678901234.pdf'
$filename -match '\d{6}_\d{8}_\d{14}\.pdf.*'

Explanation

• ^ At the start of the string
• \d+ Match at least one digit (as you said the number of digits here is unknown)
• _ Match an underscore
• \d{8} Match 8 digits
• _ Match an underscore
• \d{14} Match 14 digits
• \. Match a dot .
• pdf Match "pdf"
• $ And don't match if you are not now at the end of the string.