Write out string if it does not contain any array values in PowerShell

Question

I have a simple program here that will write out a line within an array of lines if it does not contain any of the names within another array.

[array]$names = "Adam", "Bill", "Colin", "Dave"

[array]$lines = "My name is Jim", "My name is Sam", "My name is Adam"

foreach ($line in $lines)
{
   if ($line -notmatch $names)
   {
       write $line
   }
}

When I run this, it just writes out every line from the array of lines, even though 'Adam' is included in the array of names. It should just write out 'My name is Jim' and 'My name is Sam'.

Sorry if this question is pretty basic but I couldn't find any answers for it.

Dave Sexton · Accepted Answer · 2017-05-18 13:54:18Z

3

If you are using a regex comparison with -notmatch why not turn your list of names into a better regex? How about something like this:

$names = "Adam", "Bill", "Colin", "Dave"
$lines = "My name is Jim", "My name is Sam", "My name is Adam"

$regex = $names -join '|'

$lines | ? {$_ -notmatch $regex} | % {Write-Host $_}

answered May 18, 2017 at 13:54

Dave Sexton

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1 Comment

AJennings1 Over a year ago

Thanks! I never thought of joining the strings together.

Mark Wragg · Accepted Answer · 2017-05-18 13:41:14Z

1

There is probably a better solution than this, but one way to solve it is to have a second loop that iterates through each name and checks for them in the line:

[array]$names = "Adam", "Bill", "Colin", "Dave"
[array]$lines = "My name is Jim", "My name is Sam", "My name is Adam"

foreach ($line in $lines)
{
    $names | ForEach-Object -Begin {$found = $false} {
        If ($line -match $_){ $found = $true; break } 
    } 

    if (-not $found)
    {
        write $line
    }
}

Explanation:

Sends $names via the pipeline in to ForEach-Object. This starts by initializing a $found variable within it's -Begin block.
ForEach-Object checks the line to match against each name (the name is now an item in the pipeline represented by $_). If it is found it sets $found to true and uses break to end the loop.
If $found is not true, it writes the line.

answered May 18, 2017 at 13:41

Mark Wragg

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1 Comment

AJennings1 Over a year ago

Thanks for this. Works perfect! You would think there would be simpler solutions for such a seemingly easy problem!

AJennings1 · Accepted Answer · 2017-05-18 14:02:17Z

0

Thanks for the answers guys. I have reworked my code to make it a little simpler:

[array]$names = "Adam", "Bill", "Colin", "Dave"

[array]$lines = "My name is Jim", "My name is Sam", "My name is Adam"

    foreach ($line in $lines)
    {
        $regex = $names -join '|'

        if ($line -notmatch $regex)
        {
            write $line
        }
    }

answered May 18, 2017 at 14:02

AJennings1

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