Kiron

Use where-object and -notContains to compare the collections:

$a = 'file1', 'file2', 'file3'
$b = 'file2', 'file3', 'file4'

$a | where-object {$b -notContains $_}
$b | where-object {$a -notContains $_}

# create a function
function RubySubtraction ([array]$a, [array]$b)
{
$a | where-object {$b -notContains $_}
}

# set its alias
set-alias ruby`- RubySubtraction

# call the function
RubySubtraction $a $b

# call the functi9n through its alias
ruby- $b $a

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Kiron