Last week I learned about a tool called ShellCheck, a tool for static analysis of shell scripts. It reports errors like missing double quotes, use of deprecated syntax, etc.
I decided to check some projects I contribute to, and the first issue I found was in Apache Jena:
kinow@localhost:~/Development/java/jena/jena/apache-jena/bin$ shellcheck arq In arq line 8: case "$OSTYPE" in ^-- SC2039: In POSIX sh, OSTYPE is not supported.
So, in summary, the
OSTYPE variable should not be available in POSIX shell. The case in question, where
OSTYPE is being used, checks for the Darwin OS type (i.e. Mac OS). Knowing how things get weird when you
use different operating systems, I decided to check and learn how
OSTYPE works. Here’s what I found.
- In Ubuntu, with /bin/bash, OSTYPE works fine (linux-gnu)
- In Ubuntu, with /bin/sh, OSTYPE is not set
- In Mac OS, with /bin/sh, OSTYPE is set (darwin15)
I checked the shells to make sure they were not pointing to symbolic links - some distributions use a different default shell, and replace /bin/bash and/or /bin/sh by a link to another shell. Looks like Mac OS has a POSIX shell that behaves different than Ubuntu’s.
Instead of trying to find a way to use
OSTYPE, I decided to spend some time looking at
how other projects do the same thing. And the best example I could find was
Instead of relying on
OSTYPE, git uses
I will spend some time during the next days working on a proposal to replace the
from Apache Jena scripts, but then may have to submit more changes for the other issues
found by ShellCheck.