Bash中嵌套命令的STDOUT

Question

Quite new to bash - I'm trying to store the output of my /usr/bin/time command into the TIME_INFO variable, which works with the below setup... however I would also like to be able to store the output of some of the other nested commands (such as /usr/local/bin/firejail or ./program) to other variables. Currently if there is a runtime exception in ./program it'll also go to the TIME_INFO variable.

TIME_INFO=$( /usr/bin/time --quiet -f "%e-%U-%S-%M-%x" 2>&1 \
timeout 5s \
/usr/local/bin/firejail --quiet --cgroup=/sys/fs/cgroup/memory/group1/tasks --profile=java.profile \
./program < test.in > test.out )

Is there any way to accomplish separating outputs of multiple nested commands?

Thanks in advance!

Answer 1

One way to do this is to inject a shell in the call chain and make it responsible for modifying stderr for its subprocesses:

time_info=$( /usr/bin/time --quiet -f "%e-%U-%S-%M-%x" 2>&1 \
  sh -c '"$@" 2>"$0"' test.err \
    timeout 5s \
      /usr/local/bin/firejail \
          --quiet --cgroup=/sys/fs/cgroup/memory/group1/tasks --profile=java.profile \
        ./program < test.in > test.out )

# read your content back into a shell variable
error_text=$(<test.err)

The pertinent change here is sh -c '"$@" 2>"$0" , which runs its arguments as a command, with stderr redirected to the filename passed in $0 -- which is populated from the string immediately following code passed with sh -c .

_{Note that I modified the case of the TIME_INFO variable per POSIX guidance specifying all-caps names for variables with meaning to the shell or OS, and reserving names with at least one lower-case character for other purposes.}