When comparing zsh vs DASH, the Slant community recommends zsh for most people. In the question“What are the best UNIX shells?” zsh is ranked 2nd while DASH is ranked 8th. The most important reason people chose zsh is:
When you start typing a command, you can press the tab key and it will complete the command you started typing. If there are multiple potential commands, you can choose which one to run by simply pressing tab again. Case-insensitive by default, too.
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Pros
Pro Interactive autocompletion
When you start typing a command, you can press the tab key and it will complete the command you started typing. If there are multiple potential commands, you can choose which one to run by simply pressing tab again. Case-insensitive by default, too.
Pro Powerful community-driven tools via oh-my-zsh
Oh-my-zsh is a community-driven framework, which helps users with their zsh configuration and plugins. 400 plugins, 200+ themes and auto-updates to always be up to date.
Pro Autocomplete for options
Zsh intelligently determines if you are trying to complete a file path or an option, and pressing tab after typing -
will reliably bring up a list of options.
Pro Good bash compatibility
Things you've learned using bash will largely apply to zsh. Scripts written in bash will run with little to no modification.
Pro Safer variable behaviour
Unlike Bash, zsh does not split unquoted variables by default, making it less error-prone.
Pro Recursive globbing
ls **/*.log
for example is supported by ZSH.
Pro Great install procedure
Zsh will take you through a procedure which is roughly 30 minutes in length before during install. Through this procedure it asks you to set different options and customize the shell the way you want it to. Most of these settings are also found in other shells, but to customize them you have to go dig configuration files while zsh allows you to do it in the beginning.
Pro Shared histories
If you spend a lot of time in the terminal, most likely you will have several terminal windows open. Zsh has great support for command line histories. The history is unique and shared through all the different instances.
Pro Smart escaping
Zsh can determine the context of the command you're typing in and determine if it should escape characters if you're typing in a URI.
Pro Pipe output to a temporary file:
Some programs don't support loading from stdin, but ZSH can store outputs to a temporary file, example: unzip =(curl http://example.com/someZipFile.zip)
Pro Faster spelling correction
Zsh' s correct (or correctall) is vastly superior to Bash's attempt at spelling correction.
Pro Fast startup
Dash has a very fast startup, this happens because the shell is started a lot of times during boot and dash minimizes the work it does during this process.
Pro Low memory usage, which matters a lot in embedded
It is designed to be very lightweight and has no support for shell specific extensions that are not POSIX.
Pro Default shell on Debian systems
DASH is the default shell for Debian based systems due to it speed, full POSIX compliance and low overhead.
Pro Full POSIX support
It's fully POSIX compatible, so if your script runs on dash it will probably run on all other shells.
Pro A perfect clone
It's a clone of the original System V4 Bourne shell.
Cons
Con Not fully compatible with bash
There is a small chance you may have a bash script that doesn't work in zsh, although this is very very rare and most developers will never run into any issues.
Con Requires a lot of configuration to be used fully
Zsh requires a lot of tinkering with configuration files and downloading plugins in order to be able to do tasks which other shells may be able to do out of the box.
Con Defaults are unfriendly for a long-time bash user
Expect to find a configuration you like (or use the configuration utility) to set reasonable preferences. Default zsh interaction is different enough to make you stutter through what used to be familiar workflows.
Con Doesn't support all bash features
Dash does not support all bash features, sometimes called 'bashisms' unless explicitly pointed at /bin/sh
.