jenkins/war/resources/help/project-config/shell.html

<div>
  Runs a shell script (defaults to <tt>sh</tt>, but this is configurable) for building the project.
  The script will be run with the workspace as the current directory. Type in the contents of your shell
  script. If your shell script has no header line like <tt>#!/bin/sh</tt> &mdash;, then the shell configured
  system-wide will be used, but you can also use the header line to write script in another language
  (like <tt>#!/bin/perl</tt>) or control the options that shell uses.

  <p>
  By default, the shell will be invoked with the "-ex" option. So all of the commands are printed before being executed,
  and the build is considered a failure if any of the commands exits with a non-zero exit code. Again, add the
  <tt>#!/bin/...</tt> line to change this behavior.

  <p>
  As a best practice, try not to put a long shell script in here. Instead, consider adding the shell script
  in SCM and simply call that shell script from Hudson, so that you can track changes in your shell script.
</div>