Redirecting both STDOUT and STDERR
suggest changeFile descriptors like 0
and 1
are pointers. We change what file descriptors point to with redirection. >/dev/null
means 1
points to /dev/null
.
First we point 1
(STDOUT
) to /dev/null
then point 2
(STDERR
) to whatever 1
points to.
# STDERR is redirect to STDOUT: redirected to /dev/null,
# effectually redirecting both STDERR and STDOUT to /dev/null
echo 'hello' > /dev/null 2>&1
This can be further shortened to the following:
echo 'hello' &> /dev/null
However, this form may be undesirable in production if shell compatibility is a concern as it conflicts with POSIX, introduces parsing ambiguity, and shells without this feature will misinterpret it:
# Actual code
echo 'hello' &> /dev/null
echo 'hello' &> /dev/null 'goodbye'
# Desired behavior
echo 'hello' > /dev/null 2>&1
echo 'hello' 'goodbye' > /dev/null 2>&1
# Actual behavior
echo 'hello' &
echo 'hello' & goodbye > /dev/null
NOTE: &>
is known to work as desired in both Bash and Zsh.
Found a mistake? Have a question or improvement idea?
Let me know.
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