Dash is a Unix shell, specifically the Debian Almquist Shell, that aims to be a lightweight and efficient alternative to other shells like Bash. It is a modern implementation of the POSIX standard shell (sh) and is not fully compatible with the Bash shell. Here are some key points about Dash:
- POSIX Compliance: Dash is designed to adhere to the POSIX (Portable Operating System Interface) standard for shell scripting. This means that scripts written in Dash should be portable and compatible with other POSIX-compliant shells. It provides a subset of the features and functionalities found in Bash, focusing on simplicity and efficiency.
- Performance: Dash is known for its fast startup time and low memory footprint. It is optimized for speed and resource efficiency, making it suitable for systems with limited resources or for scenarios where quick script execution is crucial.
- Script Execution: Dash can execute shell scripts written in sh syntax. It supports the common shell constructs, such as variables, loops, conditionals, functions, and pipelines. However, since it is not fully Bash-compatible, some advanced features and syntax found in Bash may not be available in Dash.
- Shell Interactivity: Dash can also be used as an interactive shell, allowing users to enter commands and execute them interactively. While it may lack some of the interactive features found in more feature-rich shells like Bash, it provides a minimalistic and efficient command line environment.
- Script Portability: Dash’s focus on POSIX compliance makes it a good choice for writing scripts that need to run across different Unix-like systems. By avoiding Bash-specific features, Dash scripts can be more easily adapted and run on various platforms without requiring modifications.
- System Shell: On some Unix-like systems, Dash may be used as the system shell (/bin/sh) instead of Bash or other shells. This choice is often made to optimize system startup time or to reduce dependencies on larger shell implementations.
- Availability: Dash is open source software and is available as a package on many Linux distributions. It can be installed alongside other shells, allowing users to choose the shell that best suits their needs.
While Dash may not have all the advanced features and interactive capabilities of shells like Bash, it excels in its simplicity, speed, and adherence to the POSIX standard. It is well-suited for scripting tasks that require fast execution, portability, and compatibility with other POSIX-compliant shells.
dash Command Examples
1. Start an interactive shell session:
# dash
2. Execute specific [c]ommands:
# dash -c "echo 'dash is executed'"
3. Execute a specific script:
# dash /path/to/script.sh
4. Check a specific script for syntax errors:
# dash -n /path/to/script.sh
5. Execute a specific script while printing each command before executing it:
# dash -x /path/to/script.sh
6. Execute a specific script and stop at the first [e]rror:
# dash -e /path/to/script.sh
7. Execute specific commands from stdin:
# echo "echo 'dash is executed'" | dash