Redirecting command output to a variable in bash fails

问题

I'm trying to redirect command output to a variable:

OUTPUT=$(sudo apache2ctl configtest)

and then to read it:

echo $OUTPUT

When running it the output is the following:

19:19:12 user@user ~ OUTPUT=$(sudo apache2ctl configtest)
Syntax OK
Syntax OK

But the variable stays blank. I've tried the same for other commands and everything works fine.

OUTPUT=$(ls -l)

This writes file list to variable OUTPUT so that it can be read later. What should i do to make it work?

回答1:

maybe the output goes to stderr, not stdout?

try this: OUTPUT=$(sudo apache2ctl configtest 2>&1)

回答2:

For nginx possible situation when configtest can be successful with error in config files. Example:

nginx: [warn] conflicting server name "test.com" on 0.0.0.0:80, ignored
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful

for correct check errors in bash scripts need use:

if [[ $((sudo /sbin/service nginx configtest) 2>&1 | grep "failed\|warn" ) ]]; then
    echo "ERROR!!!"
else
    echo "OK!!!"
fi

来源：https://stackoverflow.com/questions/10319745/redirecting-command-output-to-a-variable-in-bash-fails