Cycling through multiple variables in for loop - powershell

Question

I just started working with Powershell and this is my first script.
I am checking for 3 strings in last 50 lines of a log file. I need to find all three strings and print error message if any one of those is missing. I have written following script but it does not give me the expected results.
(Get-Content C:\foo\bar.log )[-1..-50] | Out-File C:\boom\shiva\log.txt
$PO1 = Get-Content C:\boom\shiva\log.txt | where {$_ -match "<Ping:AD_P01_RCV> ok"}
$PO2 = Get-Content C:\boom\shiva\log.txt | where {$_ -match "<Ping:AD_P02_SND> ok"}
$PO3 = Get-Content C:\boom\shiva\log.txt | where {$_ -match "<Ping:AD_P03_RCV> ok"}
I am satisfied with above piece of code. The problem is with the below. I dont want to use if-else thrice. I am struggling to draft a for loop which can save space and still give me the same result.
if (!$PO1)
{
"PO1 is critical"
}
else
{
"PO1 is OK"
}
if (!$PO2)
{
"PO2 is critical"
}
else
{
"PO2 is OK"
}
if (!$PO3)
{
"PO3 is critical"
}
else
{
"PO3 is OK"
}
Can someone gave me small example of how i can fit these 3 if-else in one for loop.

Answer 1

If you only want to find out that all 3 strings are present this script will also show which one is missing.
(binary encoded in the variable $Cnt)
## Q:\Test\2018\07\13\SO_51323760.ps1
##
$Last50 = Get-Content 'C:\foo\bar.log' | Select-Object -Last 50
$Cnt = 0
if ($Last50 -match "<Ping:AD_P01_RCV> ok"){$Cnt++}
if ($Last50 -match "<Ping:AD_P02_SND> ok"){$Cnt+=2}
if ($Last50 -match "<Ping:AD_P03_RCV> ok"){$Cnt+=4}
if ($cnt -eq 7){
"did find all 3 strings "
} else {
"didn't find all 3 strings ({0})" -f $cnt
}
Variant immediately complaining missing P0(1..3)
$Last50 = Get-Content 'C:\foo\bar.log' | Select-Object -Last 50
if (!($Last50 -match "<Ping:AD_P01_RCV> ok")) {"PO1 is critical"}
if (!($Last50 -match "<Ping:AD_P02_SND> ok")) {"PO2 is critical"}
if (!($Last50 -match "<Ping:AD_P03_RCV> ok")) {"PO3 is critical"}
Sorry I'm a bit slow this monday.
To check in a loop different variables by building the variable name:
1..3| ForEach-Object {
If (!(Get-Variable -name "P0$_").Value){"`$P0$_ is critical"}
}

Answer 2

What you're trying to do is better addressed with a hashtable than with individually named variables.
$data = Get-Content 'C:\boom\shiva\log.txt'
$ht = #{}
1..3 | ForEach-Object {
$key = 'P{0:d2}' -f $_
$str = if ($_ -eq 2) {"${key}_SND"} else {"${key}_RCV"}
$ht[$key] = $data -match "<ing:AD_${str}> ok"
}
$ht.Keys | ForEach-Object {
if ($ht[$_]) {
"${key} found in log."
} else {
"${key} not found in log."
}
}
You can check if all lines were present at least once with something like this:
if (($ht.Values | Where-Object { $_ }).Count -lt 3) {
'Line missing from log.'
}

Answer 3

PSv3 introduced the -Tail (-Last) parameter to Get-Content, which is the most efficient way to extract a fixe number of lines from the end of a file.
You can pipe its output to Select-String, which accepts an array of regex patterns, any of which produces a match (implicit OR logic).
$matchingLines = Get-Content -Tail 50 C:\foo\bar.log |
Select-String '<Ping:AD_P01_RCV> ok', '<Ping:AD_P02_SND> ok', '<Ping:AD_P03_RCV> ok'
if ($matchingLines) { # at least 1 of the regexes matched
$matchingLines.Line # output the matching lines
} else { # nothing matched
Write-Warning "Nothing matched."
}

Answer 4

I finally got below draft that resolved my query to cycle variables through a for loop. I finally had to convert those individual variables to a array. But htis gives me expected result. Basically i need this script to provide input to my Nagios plugin which needs minor modification but its done.
(Get-Content C:\foo\bar.log )[-1..-50] | Out-File C:\boom\shiva\log.txt
$j = 1
$PO = new-object object[] 3
$PO[0] = Get-Content C:\boom\shiva\log.txt | where {$_ -match "<Ping:AD_P01_RCV> ok"}
$PO[1] = Get-Content C:\boom\shiva\log.txt | where {$_ -match "<Ping:AD_P02_SND> ok"}
$PO[2] = Get-Content C:\boom\shiva\log.txt | where {$_ -match "<Ping:AD_P03_RCV> ok"}
foreach( $i in $PO){
if (!$i){
"PO "+$j+" is CRITICAL"}
else{
"PO "+$j+" is OK"}
$j+=1
}
Thank you LotPings, Ansgar and mklement0 for your support and responses. I picked up a few things from your answers.