Hi Sean, On Wed, May 23, 2012 at 01:40:51PM -0400, Sean Abbott wrote: > I'm writing my first upstart job to run selenium2 as a service on VMs. > This was my first hack: > http://paste.ubuntu.com/1003268/
> It didn't work, and after adding the suggested environment variable > lines to debug my environment, I found out it's because the variables > aren't expanding as I expected. In the pastebin version, they expand > like so: > SELENIUM_EXEC='java -jar $SELENIUM_JAR' > So, I saw that in *some* of the examples, variable appear to be escaped > by single quotes (like here: http://upstart.ubuntu.com/cookbook/#env), > so I tried, > SELENIUM_EXEC="java -jar '$SELENIUM_JAR'" > and then my environment output was: > SELENIUM_EXEC='java -jar '"'"'$SELENIUM_JAR'"'" #yes, this is a ton of > alternating single and double quotes > So, I have two questions. Which usage of variables is correct if you > are going to expand them? This one: > http://upstart.ubuntu.com/cookbook/#env > or this one: > http://upstart.ubuntu.com/cookbook/#environment-variables # (scroll to > the 'as another example' part.) Well, both of those uses are "correct", but they don't do what you seem to believe they do. http://upstart.ubuntu.com/cookbook/#env: env myvar="hello world" script echo "myvar='$myvar'" > /run/script.log end script There is no escaping going on here. Those single quotes are being used as part of a shell script to represent single quotes in the output - nothing more. The real issue here is that you want nested expansion of variables, which upstart is not going to do for you. You need a full shell and some eval's if you want that. When you do this in shell: SELENIUM_HOME="/opt/selenium" SELENIUM_JAR="${SELENIUM_HOME}/selenium-server-standalone-2.21.0.jar" SELENIUM_EXEC="java -jar $SELENIUM_JAR" the variable substitutions are expanded *when the variable is set*, which means the actual value of SELENIUM_EXEC in a shell is: $ echo $SELENIUM_EXEC java -jar /opt/selenium/selenium-server-standalone-2.21.0.jar $ With upstart's 'env' command, there's no such variable substitution; so SELENIUM_EXEC is set to the literal string "java -jar $SELENIUM_JAR"; i.e., equivalent to this bit of shell: SELENIUM_EXEC="java -jar \$SELENIUM_JAR" When calling 'exec', upstart helpfully does one level of expansion for you, which is consistent with what a shell would do. But that's it - if you need nested expansion you have to care for this yourself with calls to eval. > Second: can someone give me a hint as to how to get variable expansion > to work as expected? pre-start script test -e $(eval echo $SELENIUM_JAR) || { stop; exit 0; } mkdir -p -m0755 /var/run/selenium end script script exec $(eval echo $(eval echo $SELENIUM_EXEC)) $(eval echo $SELENIUM_OPTS) end script But for my part, I'm skeptical of the value of setting these as separate variables when they're only used once. I would write this whole thing as: env SELENIUM_EXEC="java -jar $SELENIUM_JAR" env SELENIUM_JAR="/opt/selenium/selenium-server-standalone-2.21.0.jar" env SELENIUM_OPTS="-role node -hub http://10.254.0.151:4444/grid/register"; pre-start script test -e $SELENIUM_JAR || { stop; exit 0; } mkdir -p -m0755 /var/run/selenium end script script exec $(eval echo $SELENIUM_EXEC) $SELENIUM_OPTS end script HTH, -- Steve Langasek Give me a lever long enough and a Free OS Debian Developer to set it on, and I can move the world. Ubuntu Developer http://www.debian.org/ [email protected] [email protected]
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