Tail a file in Windows

This PowerShell one-liner is a convenient way to monitor log files in real-time and quickly spot error messages. The script continuously reads the log and highlights lines that contain the word “error” with a red background, making them easy to identify. It’s a handy tool for troubleshooting or monitoring system activities, especially when dealing with logs generated by tools like DISM.

gc .\dism.log -wait |foreach-object { if ($_ -match "error"){write-host -foregroundcolor white -BackgroundColor red $_} else {write-host $_}}

Explanation:

1. gc .\dism.log -wait
   • gc is short for Get-Content, a PowerShell cmdlet that reads the content of a file.
   • .\dism.log specifies the file to read, which is dism.log. This log file is typically generated by the Deployment Imaging Service and Management Tool (DISM), often used for Windows image management.
   • The -wait parameter makes Get-Content continuously monitor the log file in real-time, displaying new content as it is written to the file. This is especially useful for live monitoring of logs.
2. | foreach-object
   • The | symbol (pipeline) sends the output of the Get-Content cmdlet to the next part of the command.
   • foreach-object is a loop that processes each line of the log file one by one as it is being read.
3. if ($_ -match "error")
   • $_ represents the current line of the log file being processed in the loop.
   • -match "error" checks if the current line contains the word “error” (case-insensitive by default in PowerShell). This is the key part that identifies lines with errors in the log.
4. write-host -foregroundcolor white -BackgroundColor red $_
   • If the line contains the word “error,” this part of the command prints it to the console with a white foreground (text color) and a red background for visibility, signaling an error.
   • $_ again represents the line being processed.
5. else { write-host $_ }
   • If the line doesn’t contain “error,” it simply prints the line normally, without any special formatting.

Example:

Suppose you are monitoring the dism.log file and a line like this is written to the log:

2024-10-11 14:55:12, Error DISM DISM.EXE: Failed to load the provider

In the console, this line will be printed in white text with a red background, making it easy to spot among other log entries.