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Unable to log output of "apachectl configtest" to a file

I want to log the output of the command "apachectl configtest" to a file. So I tried the following commands:

root@ubuntu:~# echo $(apachectl -t) >> /tmp/apache_config_check
[Sun Feb 21 14:35:23.614947 2016] [proxy_html:notice] [pid 29249] AH01425: I18n support in mod_proxy_html requires mod_xml2enc. Without it, non-ASCII characters in proxied pages are likely to display incorrectly.
Syntax OK

But It gave empty output:

root@ubuntu:~# cat /tmp/apache_config_check 

root@ubuntu:~#

I also tried a variation on the command itself:

root@ubuntu:~# apachectl -t >> /tmp/apache_config_check

and a variation on tee:

root@ubuntu:~# $(apachectl -t) | tee /tmp/apache_config_check

Without luck.

I don't really know any other methods to pipe the output, nor I know why the above commands failed. Is it something fundamental?

10 months ago · Santiago Trujillo

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Accepted Answer · 2022-04-21T20:02:46.450Z

The problem is that apachectl is sending its output to STDERR instead of STDOUT. So, you need to redirect STDERR as follows:

apachectl -t > /tmp/apache_config_check 2>&1

The 2>&1 is shell-script magic saying "redirect output on file descriptor 2 (STDERR) to file descriptor 1 (STDOUT)".