Question

I’m trying to run the Apache startup script, /etc/init.d/httpd. Environment variable definitions like this one give an error:

CONF_FILE=$(APACHE_HOME)/conf/httpd.conf  

It says "/etc/init.d/httpd: line 15: APACHE_HOME: command not found"

So, I replaced the parentheses with curly brackets, and the script worked swimmingly. What gives? I’m really just asking this question because I want to understand why it’s wrong, not how to fix it. The shebang is there, and it’s unmodified from the original shell script, so why’s it misinterpreting things?

Answer 1

In unix systems:

$SOMETHING /* variable */
$(SOMETHINGELSE) /* command */
${FOO} */ variable substitution */