Converting to Powershell - regex

Question

I have this perl code I am trying to convert to powershell.
foreach my $f ( #file_list ) {
if( $f =~ /^([\d]+)_${base_ver}_([\d]{4})\.zip$/i ){
$pfile = $f;
( $pnum, $pdate ) = ( $pfile =~ /^([\d]+)_${base_ver}_([\d]{4})\.zip$/i ); # need to convert
( $pmon, $pyear ) = ( $pdate =~ /^(\d\d)(\d\d)$/ ); # need to convert
if( ($patch_nbr == 0) || ($patch_nbr == $pnum) ) {
$fcnt++;
}
}
}
I've converted most of it here..
$file_list = Get-ChildItem -force $base_dir
$file_list | foreach-object {
if($_ -match "/^([\d]+)_${base_ver}_([\d]{4})\.zip$/i"){
$pfile = $_
if($patch_nbr -eq 0 -or $pacth_nbr -eq $pnum){
$fcnt++
}
}
}
Not quite sure how to convert the two variables that equal the regex or if there is a better way to convert the perl code to powershell than what I already have.

Answer 1

The [mode]/pattern/[replace/][options] syntax from perl doesn't apply to regex in PowerShell.
Thus, your pattern
/^([\d]+)_${base_ver}_([\d]{4})\.zip$/i
becomes
^([\d]+)_${base_ver}_([\d]{4})\.zip$
(i is unnecessary, -match resolves to -imatch (case-insensitive match) by default)
To capture the number prefix and date, you can use a named capture group ((?<name>pattern)):
^(?<num>[\d]+)_${base_ver}_(?<date>[\d]{4})\.zip$
You can then grab the match from $Matches["name"]:
if($f -match "^(?<num>[\d]+)_${base_ver}_(?<date>[\d]{4})\.zip$"){
$pfile = $f
$pnum = $Matches["num"]
$pdate = $Matches["date"]
$pmon = -join $pdate[0..1]
$pyear = -join $pdate[2..3]
}
You could also change the regex pattern to capture the month and year individually:
if($f -match "^(?<num>[\d]+)_${base_ver}_(?<month>[\d]{2})(?<year>[\d]{2})\.zip$"){
$pfile = $f
$pnum = $Matches["num"]
$pmon = $Matches["month"]
$pyear = $Matches["year"]
}

Answer 2

I would put a Where-Object filter first. That allows you to use the $matches collection in the subsequent ForEach-Object without a second -match in a nested if statement. If you also change the date pattern from (\d{4}) to (\d{2})(\d{2}) you can assign $pnum, $pmon, and $pyear in a single statement. You could also simplify the condition for incrementing $fcnt. Instead of checking if $patch_nbr equals one of two values you could check if it's contained in an array of the two values.
Get-ChildItem -Force $base_dir |
Where-Object { $_ -match '^(\d+)_${base_ver}_(\d{2})(\d{2})\.zip$' } |
ForEach-Object {
$pnum, $pmon, $pyear = $matches[1..3]
if (0, $pnum -contains $patch_nbr) { $fcnt++ }
}
}
Of course, if all you want to do is count the number of files matching a given patch number, you could just do something like this:
$f = Get-ChildItem -Force $base_dir | Where-Object {
$_ -match '^(\d+)_${base_ver}_\d{4}\.zip$' -and
0, $matches[1] -contains $patch_nbr
}
$fcnt = #($f).Count