tee, or pass filenames instead.
grep foo < input1 < input2 > output1 > output2 > output3
# Merge inputs into a single stream, write outputs individually cat input1 input2 | grep foo | tee output1 output2 > output3 # Pass inputs as filenames, write outputs individually grep foo input1 input2 | tee output1 output2 > output3
A file descriptor, whether stdin, stdout, stderr, or non-standard ones, can only point to a single file/pipe.
For input, many commands support processing multiple filenames. In these cases you can just specify the filenames instead of redirecting. Alternatively, you can use
cat to merge multiple filenames into a single stream.
For output, you can use
tee to write to multiple output sinks in parallel.
Zsh will automatically
cat inputs and
tee outputs, but none of the shells supported by ShellCheck do.
ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.