filter string from live (updating) log file using windows powershell

Question

I have a computer that is logging events from a device on a serial port. Putty is logging them to a file.

I used to have this running on a Linux machine. Basically would tail -f event.log >> script.sh

This was the *nix script

#!/bin/bash

outfile=sras_pages.log

while read -r line
do
    IFS=' ' read -ra split <<< "$line"
    [[ ${split[1]} == AC/BATT_PWR ]] && echo "${line:9:29}"
    [[ ${split[1]} == COMM-FAULT ]] && echo "${line:9:29}"
done >> "$outfile"

Basically I want to forward only character positions 9-29 that contain the two strings above to a file that is monitored by a paging terminal.

The Linux option is gone now and I'm stuck with windows. I've only just learned about windows PowerShell and have been trying to muck my way through it via examples i find online.

I started with this:

Get-Content -Path C:\temp\SRAS\alarm.log -tail 1 -Wait

Which gives me the tail -f functionality I got with linux. The problem is I can't figure out how to feed the output of this command into another PowerShell script.

I then cobbled this together

$p = @("AC/BATT_PWR","COMM-FAULT")
Get-Content -Path C:\temp\SRAS\alarm.log -tail 1 -Wait | Select-String -Pattern $p -SimpleMatch | Set-Content C:\temp\SRAS\sras_pages.log

Which works, EXCEPT the file sras_pages.log is only written to once I Ctrl+C in the powershell to stop it from running.

What I need is to monitor a log file that is updating regularly, and any events that match a string to be appended to a separate file when they happen.

I don't know enough about powershell to do this and am looking for some help.

Much appreciated.

Frode F. · Accepted Answer · 2015-01-18 12:22:45Z

1

Set-Content overwrites the file's contents, so it waits for all the content before it flushes and writes everything to the file. Add-Content appends to the file, which would fit better for a script that will continue to write over time, but just like Set-Content, it locks the file and flushes when the script is done or cancelled.

Out-File however also supports appending, and it does not lock the file. So you could try replacing your Set-Content command with:

Out-File -FilePath "C:\temp\SRAS\sras_pages.log" -Append

answered Jan 18, 2015 at 12:22

Frode F.

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2 Comments

k1162 Over a year ago

Thank you so much... After tinkering last night I was able to come up with this as welland it works %100. Since I got this step down I'm now on to adding more to the code. If I have further questions to this am i supposed to start a new question? I'm new to this site and the setup isn't typical of a general forum.

Frode F. Over a year ago

Yes, you are sipposed to create a new question for seperate issues. Try to search first, as we have probably answered it before for someone else. :) Check out the tour: stackoverflow.com/tour . Remember to hit the checkmark next to my answer if it solved your problem/was the best answer. Welcome to SO.

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