How to find the version of the Dash shell on Ubuntu /bin?

There are plenty of ways:

• apt-cache policy

  Run the following command:

  apt-cache policy dash
  

  On my machine the output is:

  dash:
  Installed: 0.5.7-3ubuntu1
  Candidate: 0.5.7-3ubuntu1
  Version table:
  *** 0.5.7-3ubuntu1 0
      500 http://in.archive.ubuntu.com/ubuntu/ quantal/main amd64 Packages
      100 /var/lib/dpkg/status
  

  The version of dash, therefore, installed on my system is 0.5.7.

• dpkg -s

  Run the following command:

  dpkg -s dash
  

  The output on my machine is:

  Package: dash
  Essential: yes
  Status: install ok installed
  Priority: required
  Section: shells
  Installed-Size: 213
  Maintainer: Ubuntu Developers 
  Architecture: amd64
  Version: 0.5.7-3ubuntu1
  Depends: debianutils (>= 2.15), dpkg (>= 1.15.0)
  Pre-Depends: libc6 (>= 2.14)
  Description: POSIX-compliant shell
  The Debian Almquist Shell (dash) is a POSIX-compliant shell derived
  from ash.
  .
  Since it executes scripts faster than bash, and has fewer library
  dependencies (making it more robust against software or hardware
  failures), it is used as the default system shell on Debian systems.
  Homepage: http://gondor.apana.org.au/~herbert/dash/
  Original-Maintainer: Gerrit Pape 
  

  As you can see, the version is: 0.5.7.

Understanding Versioning Conventions

The versioning in Ubuntu is of the form:

<upstream_version>-<debian_revision>ubuntu<ubuntu_revision>

Here:

• <upstream_version>: is the version of the original package

  This is the main part of the version number. It is usually the version number of the original ("upstream") package from which the .deb file has been made, if this is applicable.

  Usually this will be in the same format as that specified by the upstream author(s); however, it may need to be reformatted to fit into the package management system's format and comparison scheme.

• <debian_revision>: is the debian version of the package.

  This part of the version number specifies the version of the Debian package based on the upstream version.

  If <debian_revision> = 0, then this means that there is no debian package (or that the ubuntu team has forked a debian package to a newer version than the one found in the debian repositories).

• ubuntu: just the keyword ubuntu.

• <ubuntu_revision>: is the ubuntu version of the package.

  • If this is missing this mean that it is a clean, unchanged debian package.
  • If this is present it means that Ubuntu has taken the debian package and released it with some additional patches or bug fixes.

Let's take an example.

• 2.6.0-1ubuntu1

  Here,

  • Upstream Package Version: 2.6.0
  • Debian Revision: 1
  • Ubuntu Revision: 1

• 2.6.0-0ubuntu1

  Here,

  • Upstream Package Version: 2.6.0
  • Debian Revision: 0 (which means no revisions)
  • Ubuntu Revision: 1

Sources and Further Information:

• Debian Versioning: http://www.debian.org/doc/debian-policy/ch-controlfields.html#s-f-Version

• Ubuntu Package Versioning Explanation: http://www.ducea.com/2006/06/17/ubuntu-package-version-naming-explanation/