testing environment for shell scripts to verify their compatibility with POSIX syntax
Dash is a modern replacement for ash in Debian and was expected to be the default /bin/sh for Debian Lenny  but actually became the default /bin/sh for Debian Squeeze. Dash has been the default /bin/sh in Ubuntu since the 6.10 release in October 2006. During the transition by Ubuntu, numerous scripts making use of Bash-specific functionality (but not declaring it) were discovered. To avoid errors, Bash-specific scripts can be modified to be compatible with the appropriate standard, or explicitly declare their use of bashisms by explicitly setting the interpreter to Bash via the shebang line: #!/usr/bin/env bash.