bashcov / v1.5.0

Tree @v1.5.0 (Download .tar.gz)


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Code coverage for Bash

You should check out these coverage examples - it's worth a thousand words:


$ gem install bashcov


$ bashcov --help prints all available options. Here are some examples:

$ bashcov ./
$ bashcov --skip-uncovered ./
$ bashcov -- ./ --some --flags
$ bashcov --skip-uncovered -- ./ --some --flags can be a mere Bash script or typically your CI script. Bashcov will keep track of all executed scripts.

Then it will create a directory named ./coverage/ containing nice HTML files. Open ./coverage/index.html to browse the coverage report.

SimpleCov integration

You can take great advantage of SimpleCov by adding a .simplecov file in your project's root (like this). See SimpleCov README for more information.

Some gory details

Figuring out where an executing Bash script lives in the file system can be surprisingly difficult. Bash offers a fair amount of introspection into its internals, but the location of the current script has to be inferred from the limited information available through BASH_SOURCE, PWD, and OLDPWD (and potentially DIRSTACK if you are using pushd/popd). For this purpose, Bashcov puts Bash in debug mode and sets up a PS4 that expands the values of these variables, reading them on each command that Bash executes. But, given that:

  • BASH_SOURCE is only an absolute path if the script was invoked using an absolute path,
  • the builtins cd, pushd, and popd alter PWD and OLDPWD, and
  • none of these variables are read-only and can therefore be unset or otherwise altered,

it can be easy to lose track of where we are.

"Wait a minute, what about pwd, readlink, and so on?" That would be great, except that subshells executed as part of expanding the PS4 can cause Bash to report extra executions for certain lines. Also, subshells are slow as the PS4 is expanded on each and every command when Bash is in debug mode.

To deal with these limitations, Bashcov uses the expedient of maintaining two stacks that track changes to PWD and OLDPWD. To determine the full path to the executing script, Bashcov iterates in reverse over the PWD stack, testing for the first $PWD/$BASH_SOURCE combination that refers to an existing file. This heuristic is susceptible to false positives -- under certain combinations of directory structure, script invocation paths, and working directory changes, it may yield a path that doesn't refer to the currently-running script. However, it performs well under the various working directory changes performed in the test app demo and avoids the spurious extra hits caused by using subshells in the PS4.

One final note on innards: Bash 4.3 fixed a bug in which PS4 expansion is truncated to a maximum of 128 characters. On platforms whose Bash version suffers from this bug, Bashcov uses the ASCII record separator character to delimit the PS4 fields, whereas it uses a long random string on Bash 4.3 and above. When the field delimiter appears in the path of a script under test or in a command the script executes, Bashcov won't correctly parse the PS4 and will abort early with incomplete coverage results.


Bug reports and patches are most welcome. See the contribution guidelines.