olof / posh

A simple shell, inspired by fish but with fewer features.

posh

posh is a shell, mostly aimed at interactive use. It is highly inspired by fish, but with fewer features.

Projects

The project is (currently) split into two crates:

• posh-core, the engine
• posh, the CLI

Goals

Before posh can be considered feature complete, the following features are required:

Tab completion

Tab completion that works on files, as well as arguments to programs. It will probably be quite simple, maybe parsing man pages (like fish) will be considered.

A simple builtin for generating completion files would also be great.

Sophisticated input parsing (done)

Currently, the input parsing always separates on space characters, returning the first entry as the command and the following as arguments. There are a few ways in which this must be improved.

Input should be lexed and then parsed into an abstract syntax tree.

Globbing and expansion

* and ** to expand to everything, non-recursively and recursively, respectively. Environment variable expansion by $. Command substitution by $(). Brace expansion by {}. Skipping separation by wrapping multiple words in either single quotes or double quotes, the latter expanding variables within.

Piping (done)

Laying down pipes by separating statements with |, which makes the process redirect its stdout to the following process's stdin.

Redirections (done)

Redirecting the stdout (and stderr) streams with >, >>, 2>, etc. As well as the stdin stream with <.

Environment variables (done)

Part of this ties in with the globbing and expansion section, but to support environment variables fully one should be able to set them on a process basis (i.e. FOO=BAR ls), and exporting them to the current session.

Configurability

The shell should be able to execute arbitrary files, reading one (or some) of them at login. Most likely in $XDG_CONFIG_HOME/posh/init.posh or similar.

More advanced CLI

The posh CLI should be able to accept some flags, in part in order to be POSIX compliant (I believe). Things like -c to execute something, and probably a bunch more.

More builtins

The shell needs to support looping with for, while, if statements with if [ <stmt> ]; then; else; fi, and a bunch more for POSIX compliance (and more ergonomic day to day use).

For the time builtin, something like time last to print the execution time of the previous command. This would be useful for scenarios in which you run a (maybe long-running) command, and only remember that you wanted to time it afterwards.

Rough list of wanted builtins:

• cd
• exit
• history
• time
• jobs
• fg
• if
• then
• else
• fi
• case
• esac
• for
• while
• do
• done

Current state

The shell is in heavy development and is quite unstable at the moment. The features described in goals are mostly lacking currently. The following is a high-level checklist of what is in and what is not.

• Tab completion
• Sophisticated input parsing
• Globbing and expansion
  • Expand ~ to (expanded) $HOME
  • Piping
  • Multiple commands with ; separator
  • Redirections
  • Brace expansion, {foo,bar}.txt -> foo.txt bar.txt
  • Globbing, both regular *.rs and recursive **.rs
• Environment variables
• Configurability
• More advanced CLI
  • --command flag to execute command and exit
  • --lex/--ast flags to print tokens/AST respectively and exit
  • More, currently unknown features
• Expected builtins

Contributing

posh is written in Rust, and uses cargo for building, linting, formatting, and testing. Contributing requires having the stable Rust toolchain installed. The recommended way to install this is with rustup.