Sometimes you want to weed out the “cannots.”
The following is as I recall it.
Yesterday I was in a server file system using the Linux terminal. I wanted to know about the folders the terminal could access, not the ones it couldn’t. Yet, there were more it couldn’t.
I pipelined the command into grep:
command | grep -v “cannot”
but it was still showing the “cannot” lines.
I learned from another source that the reason is grep only works on standard output, file handle 1 in the terminal, whereas “cannot” typically will come from standard error, file handle 2.
When I tried
command 2>&1 | grep -v cannot
I got what I was hoping for. Apparently 2>&1 feeds standard error into standard output, so grep can work on it.
Interesting, eh?
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