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the subshell is your friend

Today I tried to find a way to track the time of a shell-command and to log that runtime into a file. I was already aware of the time command which is a bash build-in. Due to that it passes its output directly to the user without using either stdout or stderr and therefore there’s no “easy” way to redirect the output directly into a file.

But bash als provides subshells and in this case that’s how you can use the output (which is passed on stderr in this case).

(time sleep 5) 2> time.log