A novel Unix shell

This project aims to explore the potentials of the Unix shell. It is a work in progress; things will change without warning. The issues list contains many things I'm working on.

Screenshot

Elvish looks like this:

Prebuilt binaries

64-bit Linux: curl -s https://dl.elvish.io/elvish-linux.tar.gz | sudo tar vxz -C /usr/bin

64-bit Mac OS X: curl -s https://dl.elvish.io/elvish-osx.tar.gz | sudo tar vxz -C /usr/bin

See also Building Elvish.

Getting Started

Elvish mimics bash and zsh in a lot of places. The following shows some key differences and highlights, as well as some common tasks:

• Put your startup script in ~/.elvish/rc.elv. There is no alias yet, but you can achieve the goal by defining a function:

  fn ls { e:ls --color $@ }
  

  The e: prefix (for "external") ensures that the external command named ls will be called. Otherwise this definition will result in infinite recursion.

• The left and right prompts and be customized by assigning functions to le:prompt and le:rprompt. Their outputs are concatenated (with no spaces in between) before being used as the respective prompts. The following simulates the default prompts but uses fancy Unicode:

  # "tilde-abbr" abbreviates home directory to a tilde.
  le:prompt={ tilde-abbr $pwd; put '❱ ' }
  # "constantly" returns a function that always writes the same value(s) to output.
  le:rprompt=(constantly `whoami`✸`hostname`)
  

• Press Up to search through history. It uses what you have typed to do prefix match. To cancel, press Escape.

  

• Press Tab to start completion. Use arrow key and Tab to select the candidate; press Enter, or just continue typing to accept. To cancel, press Escape.

  

• Press Ctrl-N to start navigation mode. Press Ctrl-H to show hidden files; press again to hide. Press tab to append selected filename to your command. Likewise, pressing Escape gets you back to the default (insert) mode.

  

• Try typing echo [ and press Enter. Elvish knows that the command is unfinished due to the unclosed [ and inserts a newline instead of accepting the command. Moreover, common errors like syntax errors and missing variables are highlighted in real time.

• Elvish remembers which directories you have visited. Press Ctrl-L to list visited directories. Like in completion, use Up, Down and Tab to navigate and use Enter to accept (which cds into the selected directory). Press Escape to cancel.

  

  Type to filter:

  

  The filtering algorithm takes your filter and adds ** to both sides of each path component. So g/di becomes pattern **g**/**di**, so it matches /home/xiaq/go/elves/elvish/edit.

• NOTE: Default key bindings as listed above are subject to change in the future; but the functionality will not go away.

• Elvish doesn't support history expansion like !!. Instead, it has a "bang mode", triggered by Alt-,, that provides the same functionality. For example, if you typed a command but forgot to add sudo, you can then type sudo and press Alt-, twice to fix it:

  

• Lists look like [a b c], and maps look like [&key1=value1 &key2=value2]. Unlike other shells, a list never expands to multiple words, unless you explicitly splice it by prefixing the variable name with $@:

  ~> li=[1 2 3]
  ~> for x in $li; do echo $x; done
  [1 2 3]
  ~> for x in $@li; do echo $x; done
  1
  2
  3
  

• You can manipulate search paths through the special list $paths:

  ~> echo $paths
  [/bin /sbin]
  ~> paths=[/opt/bin $@paths /usr/bin]
  ~> echo $paths
  [/opt/bin /bin /sbin /usr/bin]
  ~> echo $e:PATH
  /opt/bin:/bin:/sbin:/usr/bin
  

• You can manipulate the keybinding through the map $le:binding. For example, this binds Ctrl-L to clearing the terminal: le:binding[insert][Ctrl-L]={ clear > /dev/tty }. The first index is the mode and the second is the key. (Yes, the braces enclose a lambda.)

  Use pprint $le:binding to get a nice (albeit long) view of the current keybinding.

• Environment variables live in a separate E: (for "environment") namespace and must be explicitly qualified:

  ~> put $E:HOME
  ▶ /home/xiaq
  ~> E:PATH=$E:PATH":/bin"
  

  NOTE: The E: and e: namespaces are actually the same namespace. However, since command names are typically in lower case while environment variables are typically in upper case, e: fits external commands better and E: fits environment variables better.

• There is no interpolation inside double quotes (yet). Use implicit string concatenation:

  ~> name=xiaq
  ~> echo "My name is "$name"."
  My name is xiaq.
  

• Elementary floating-point arithmetics as well as comparisons are builtin. Unfortunately, you have to use prefix notation:

  ~> + 1 2
  ▶ 3
  ~> / `* 2 3` 4
  ▶ 1.5
  ~> / (* 2 3) 4 # parentheses are equivalent to backquotes, but look nicer in arithmetics
  ▶ 1.5
  ~> > 1 2 # ">" may be used as a command name
  false
  ~> < 1 2 # "<" may also be used as a command name; silence means "true"
  

• Functions are defined with fn. You can name arguments:

  ~> fn square [x]{
       * $x $x
     }
  ~> square 4
  ▶ 16
  

• Output of some builtin commands start with a funny "▶". It is not part of the output itself, but shows that such commands output a stream of values instead of bytes. As such, their internal structures as well as boundaries between values are preserved. This allows us to manipulate structured data in the shell; more on this later.

Building Elvish

Go >= 1.5 is required. Linux is fully supported. It is likely to work on BSDs and Mac OS X. Windows is not supported yet.

The main binary can be installed using go get github.com/elves/elvish. There is also an auxiliary program called elvish-stub; install it with make stub. Elvish is functional without the stub, but job control features depend on it.

If you are lazy and use bash or zsh now, here is something you can copy-paste into your terminal:

export GOPATH=$HOME/go
export PATH=$PATH:$GOPATH/bin
mkdir -p $GOPATH

go get github.com/elves/elvish
make -C $GOPATH/src/github.com/elves/elvish stub

for f in ~/.bashrc ~/.zshrc; do
    printf 'export %s=%s\n' GOPATH '$HOME/go' PATH '$PATH:$GOPATH/bin' >> $f
done

How To Write Go Code explains how $GOPATH works.

For macOS users, you can build elvish via homebrew:

brew install --HEAD elvish

Name

In roguelikes, items made by the elves have a reputation of high quality. These are usually called elven items, but I chose elvish for an obvious reason.

The adjective for elvish is also "elvish", not "elvishy" and definitely not "elvishish".