GNU screen: "-X: unknown command 'hardcopy -h'

[^rooker]

[PROBLEM]
I've finally discovered that GNU screen is not only good handling persistent sessions, but you can also remote-control a screen session by sending commands to it.

I wanted to take like a "screenshot" of a runnign session, by using the screen command "hardcopy" with a target filename, like this:

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screen -S "session_name" -X 'hardcopy "/tmp/test.log"'

Unfortunately, I received the following error message in the target session:

-X: unknown command 'hardcopy "/tmp/test.log"'

However, without arguments, it worked fine:

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screen -S "session_name" -X 'hardcopy'

[SOLUTION]
If you're sending a screen command with arguments, you must not use quotes. So the right commandline call is:

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screen -S "session_name" -X hardcopy "/tmp/test.log"

Voila!

TIPP!
Using hardcopy like this is perfect for monitoring background processes without giving someone shell-access, but rather dump the hardcopies to a path accessible over the network, so users can monitor things without being able to break anything.