Using a Job within the While($true) loop of a PowerShell script - powershell

Question

If the Pattern "Idle" is found at the immediate run of the script - it successfully sends the email. The problem is it should be able to keep looking within the while($true) loop with the start-sleep interval. This is not happening - it will wait for 60 minutes and then exit - even when the pattern "Idle" was written as the last line.
do I need a while loop within the Start-Job? I tried this code using a Wait with no luck: Get-Content $file -Tail 1 -Wait | Select-string -Pattern "Idle" -Quiet
$job = Start-Job {
# Note: $file should be the absolute path of your file
Get-Content $File -Raw | Select-string -Pattern "Idle" -Quiet
}
while($true)
{
# if the job has completed
if($job.State -eq 'Completed')
{
$result = $job|Receive-Job
# if result is True
if($result)
{
$elapsedTime.Stop()
$duration = $elapsedTime.Elapsed.ToString("hh\:mm\:ss")
# .... send email logic here
# for success result
break #=> This is important, don't remove it
}
# we don't need a else here,
# if we are here is because $result is false
$elapsedTime.Stop()
$duration = $elapsedTime.Elapsed.ToString("hh\:mm\:ss")
# .... send email logic here
# for unsuccessful result
break #=> This is important, don't remove it
}
# if this is running for more than
# 60 minutes break the loop
if($elapsedTime.Elapsed.Minutes -ge 60)
{
$elapsedTime.Stop()
$duration = $elapsedTime.Elapsed.ToString("hh\:mm\:ss")
# .... send email logic here
# for script running longer
# than 60 minutes
break #=> This is important, don't remove it
}
Start-Sleep -Milliseconds 500
}
Get-Job|Remove-Job

Answer 1

You indeed need Get-Content's -Wait switch to keep checking a file for new content in (near) real time (new content is checked for once every second).
However, doing so waits indefinitely, and only ends if the target files is deleted, moved, or renamed.
Therefore, with -Wait applied, your job may never reach status 'Completed' - but there's no need to wait for that, given that Receive-Job can receive job output while the job is running, as it becomes available.
However, you mustn't use Select-String's -Quiet switch, because it will only ever output one result, namely $true once the first match is found - and will produce no further output even if content added later also matches.
Therefore, you probably want something like the following:
$job = Start-Job {
# Use Get-Content with -Wait, but don't use Select-String with -Quiet
Get-Content $File -Raw -Wait | Select-string -Pattern "Idle"
}
while ($true)
{
# Check for available job output, if any.
if ($result = $job | Receive-Job) {
$duration = $elapsedTime.Elapsed.ToString("hh\:mm\:ss")
# .... send email logic here
# for success result
break
}
# if this is running for more than
# 60 minutes break the loop
if($elapsedTime.Elapsed.Minutes -ge 60)
{
$elapsedTime.Stop()
$duration = $elapsedTime.Elapsed.ToString("hh\:mm\:ss")
# .... send email logic here
# for script running longer
# than 60 minutes
# Forcefully remove the background job.
$job | Remove-Job -Force
break
}
Start-Sleep -Milliseconds 500
}
Note:
$job | Receive-Job either produces no output, if none happens to be available, or one or more [Microsoft.PowerShell.Commands.MatchInfo] instances reported by Select-Object.
Using this command as an if-statement conditional (combined with an assignment to $result) means that one or more [Microsoft.PowerShell.Commands.MatchInfo] instances make the conditional evaluate to $true, based on PowerShell's implicit to-Boolean coercion logic - see the bottom section of this answer.