output redirection inside bsub command

问题

Is it possible to use output redirection inside bsub command such as:

bsub -q short "cat <(head -2 myfile.txt) > outputfile.txt"

Currently this bsub execution fails. Also my attempts to escape the redirection sign and the parenthesis were all failed, such as:

bsub -q short "cat \<\(head -2 myfile.txt\) > outputfile.txt"
bsub -q short "cat <\(head -2 myfile.txt\) > outputfile.txt"

*Note, I'm well aware that the redirection in this simple command is not necessary as the command could easily be written as:

bsub -q short "head -2 myfile.txt > outputfile.txt" 

and then it would indeed be executed properly (without errors). I am however interested in implementing the redirection of output '<' within the context of a more composed command, and am bringing this simple command here as an example only.

回答1:

<(...) is process substitution -- a bash extension not available on baseline POSIX shells. system(), subprocess.Popen(..., shell=True) and similar calls use /bin/sh, which is not guaranteed to have such extensions.

---

As a mechanism that works with any possible command without needing to worry about how to correctly escape it into a string, you can export that function and any variables it uses through the environment:

# for the sake of example, moving filenames out-of-band
in_file=myfile.txt
out_file=outputfile.txt

mycmd() { cat <(head -2 <"$in_file") >"$out_file"; }

export -f mycmd                # export the function into the environment
export in_file out_file        # and also any variables it uses

bsub -q short 'bash -c mycmd'  # ...before telling bsub to invoke bash to run the function

回答2:

<(...) is a bash feature while your command runs with sh.

Invoke bash explicitly to handle your bash-only features:

bsub -q short "bash -c 'cat <(head -2 myfile.txt) > outputfile.txt'"

来源：https://stackoverflow.com/questions/50609898/output-redirection-inside-bsub-command