Check if string is in list of strings

Question

Context: We are making an API to get a list of all VMs and the filter it, using if loops, to return only VMs with name starting only with the values in $MachineList.

The list of servers is split in 2:

set 1: srv-a-1, srv-a-2, srv-b-1, srv-b-2, srv-c-1, srv-c-2, etc.
set 2: tst-a-1, tst-a-2, tst-b-1, tst-b-2, tst-c-1, tst-c-2, etc.

This is the script:

$EnvironmentList = "Environments-4" -or "Environments-5" -or "Environments-41" -or "Environments-61"
$MachineList = "srv-a*" -or "srv-b*" -or "srv-c*" -or "srv-d*" -or "srv-e*" -or "srv-f*" -or "srv-g*" -or "srv-h*" -or" srv-i*" -or "srv-j*" -or "srv-k*" -or "srv-l*"

function CheckService {
    $MachinesRequest = (Invoke-WebRequest -Method Get -Headers @{"X-system-ApiKey"="Hashed-API-Key-Value"} -URI https://url-to-site.local/api/machines/all).Content | ConvertFrom-Json
    foreach ($Machine in $MachinesRequest) {
        if ($EnvironmentList -contains $Machine.EnvironmentIds) {
            if ($MachineList -contains $Machine.Name) {
                $Machine.Name
            }
        }
    }
}

CheckService

We're trying to return just the items which match the values in the machine list however this is returning the full list of machines (both srv* and tst*).

Ansgar Wiechers · Accepted Answer · 2018-07-22 16:05:31Z

10

First and foremost, $MachineList = "srv-a*" -or "srv-b*" -or ... won't do what you apparently think it does. It's a boolean expression that evaluates to $true, because PowerShell interprets non-empty strings as $true in a boolean context. If you need to define a list of values, define a list of values:

$MachineList = "srv-a*", "srv-b*", ...

Also, the -contains operator does exact matches (meaning it checks if any of the values in the array is equal to the reference value). For wildcard matches you need a nested Where-Object filter

$MachineList = "srv-a*", "srv-b*", "srv-c*", ...
...
if ($MachineList | Where-Object {$Machine.Name -like $_}) {
    ...
}

A better approach in this scenario would be a regular expression match, though, e.g.:

$pattern = '^srv-[a-l]'
...
if ($Machine.Name -match $pattern) {
    ...
}

edited Jul 22, 2018 at 16:05

answered Nov 3, 2017 at 13:12

Ansgar Wiechers

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2 Comments

Ravior Over a year ago

Why is using a regular expression a better approach in your oppinion?

Ansgar Wiechers Over a year ago

@Ravior Performance reasons. Doing a series of comparison operations generally takes longer than a single comparison operation.

ListenSoftware Louise Ai Agent · Accepted Answer · 2021-05-11 17:10:31Z

0

use -eq for an exact match. use -match or -contains for a partial string match

$my_list='manager','coordinator','engineer', 'project engineer',
$retval=$False
if ($dd_and_pm -eq "engineer")
{
    $retval=$True
}

answered May 11, 2021 at 17:10

ListenSoftware Louise Ai Agent

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