Find lines with specific characters recursively - powershell

Question

I am searching for all lines with '.png' and '.jpg' strings in them across multiple folders of TXT files.
Tried:
(Get-ChildItem K:\FILES -Recurse -Include '*.txt') | ForEach-Object {
(Get-Content $_) -match '\.png','\.jpg' | out-file K:\Output.txt
}
but it does not output anything. No error either. I did something similar recently and it was working. I am scratching my head wondering what am I doing wrong here...

Answer 1

By placing your Out-File call inside the ForEach-Object script block, you're rewriting your output file in full for every input file, so that the last input file's results - which may be none - end up as the sole content of the file.
The immediate fix is to move the Out-File call to its own pipeline segment, so that it receives all output, across all files:
Get-ChildItem K:\FILES -Recurse -Include '*.txt' |
ForEach-Object {
#(Get-Content $_) -match '\.png', '\.jpg'
} |
Out-File K:\Output.txt
Note: Technically, adding -Append to your Out-File call inside the ForEach-Object could have worked too, but this approach should be avoided:
Every Out-File call must open and close the output file, which makes the operation much slower.
You need to ensure that there is no preexisting output file beforehand - otherwise you'll end up appending to that file's existing content.
However, consider speeding up your command with the help of Select-String:
Get-ChildItem K:\FILES -Recurse -Include '*.txt' |
Select-String -Pattern '\.png', '\.jpg' |
ForEach-Object Line |
Out-File K:\Output.txt
Note:
In PowerShell (Core) 7+, you can use the -Raw switch with Select-String, which directly outputs only the text of all matching lines, in which case ForEach-Object Line isn't needed.
If you want to prefix each matching line with the source file path:
Get-ChildItem K:\FILES -Recurse -Include '*.txt' |
Select-String -Pattern '\.png', '\.jpg' |
ForEach-Object { '{0}: {1}' -f $_.Path, $_.Line } |
Out-File K:\Output.txt
Note: If you pipe Select-String output directly (without -Raw or ForEach-Object Line) to Out-File (or if you use >), you'll get similar output (even including a character position), but with limitations:
You'll get a blank line at the top and the bottom of the file.
Long line texts may be truncated.
The reason is that Out-File and its virtual alias > send the for-display representations of the input objects to the output file, which aren't meant for programmatic processing and can incur truncation of the data based on the line length (number of columns) of the current console window.