ion-shell 1.0.1

The Ion Shell
ion-shell-1.0.1 is not a library.

Ion Shell

Build Status MIT licensed Coverage Status

Ion is a shell for UNIX platforms, and is the default shell in Redox. It is still a work in progress, but much of the core functionality is complete. It is also currently significantly faster than Bash, and even Dash, making it the fastest system shell to date.

Completed Features

  • Variable Expansions
  • Brace Expansions
  • Process Expansions
  • Flow Control
  • For Loops
  • While Loops
  • If Conditionals
  • Functions
  • Executing Scripts with an @args Array
  • Aliases
  • Variables ($variable)
  • Substring Slicing of Variables
  • Arrays (@array)
  • Array Expressions ([])
  • Array-based Command Substitution (@[])
  • String-based Command Substitution ($())
  • Array Methods (@split(var, ' '))
  • String Methods ($join(array, ', '))
  • Array Splicing
  • Piping Stdout/Stderr
  • Redirecting Stdout/Stderr
  • Piping Builtins
  • && and || Conditionals
  • Background Jobs
  • Multiline Comments and Commands
  • Tab Completion (Needs Improvements)

Unimplemented Features

Currently, the most important missing feature is support for signal handling, which is not well supported by in Rust at this time due to the lack of developed signal handling crates, and Redox not having support for signal handling.

  • Signal Handling
  • Multiline Editing
  • XDG App Dirs
  • Background Jobs Control
  • Autosuggestions (90%)
  • Syntax Highlighting
  • Piping Functions
  • Maps
  • Lists?
  • Foreach Loops
  • Syntax for Color Handling
  • Builtin Plugins
  • Prompt Plugins
  • Syntax Plugins

Shell Syntax

Defining Variables

The let keyword is utilized to create local variables within the shell. The export keyword performs a similar action, only setting the variable globally as an environment variable for the operating system.

let git_branch = $(git rev-parse --abbrev-ref HEAD ^> /dev/null)

If the command is executed without any arguments, it will simply list all available variables.

Using Variables

Variables may be called with the $ sigil, where the value that follows may be a local or global value. They may also be optionally defined using a braced syntax, which is useful in the event that you need the value integrated alongside other characters that do not terminate the variable parsing.

let a = one
let b = two
echo $A:$B
echo ${A}s and ${B}s

Substrings from Variables

Ion natively supports splitting supplied strings by graphemes using the same slicing syntax for arrays:

$ let string = "one two three"
$ echo $string[0]
$ echo $string[..3]
$ echo $string[4..7]
$ echo $string[8..]

Dropping Variables

To drop a value from the shell, the drop keyword may be used:

drop git_branch

Variable Arithmetic

The let command also supports basic arithmetic.

let a = 1
echo $a
let a += 4
echo $a
let a *= 10
echo $a
let a /= 2
echo $a
let a -= 5
echo $a


The export command works similarly to the let command, but instead of defining a local variable, it defines a global variable that other processes can access.

export PATH = "~/.cargo/bin:${PATH}"

Export Arithmetic

The export command also supports basic arithmetic.

export a = 1
echo $a
export a += 4
echo $a
export a *= 10
echo $a
export a /= 2
echo $a
export a -= 5
echo $a


The alias command is used to set an alias for running other commands under a different name. The most common usages of the alias keyword are to shorten the keystrokes required to run a command and it's specific arguments, and to rename a command to something more familiar.

alias ls = 'exa'

If the command is executed without any arguments, it will simply list all available aliases.

The unalias command performs the reverse of alias in that it drops the value from existence.

unalias ls

Brace Expansion

Brace expansions are used to create permutations of a given input. In addition to simple permutations, Ion supports brace ranges and nested branches.

echo abc{3..1}def{1..3,a..c}
echo ghi{one{a,b,c},two{d,e,f}}

Defining Arrays

Arrays can be create with the let keyword when the supplied expression evaluates to a vector of values:

Array Syntax

The basic syntax for creating an array of values is to wrap the values inbetween [] characters. The syntax within will be evaluated into a flat-mapped vector, and the result can therefor be stored as an array.

let array = [ one two 'three four' ]

One particular use case for arrays is setting command arguments

let lsflags = [ -l -a ]
ls @lsflags

Braces Create Arrays

Brace expansions actually create a vector of values under the hood, and thus they can be used to create an array.

let braced_array = {down,up}vote

Array-based Command Substitution

Whereas the standard command substitution syntax will create a single string from the output, this variant will create a whitespace-delimited vector of values from the output of the command.

let word_split_process = @[echo one two three]

Using Arrays

Arrays may be called with the @ sigil, which works identical to the variable syntax:

echo @braced_array
echo @{braced_array}

Arrays may also be sliced when an index or index range is supplied:

Slice by Index

Slicing by an index will take a string from an array:

let array = [ 1 2 3 ]
echo @array[0]
echo @array[1]
echo @array[2]

echo [ 1 2 3 ][0]
echo [ 1 2 3 ][1]
echo [ 1 2 3 ][2]

echo @[echo 1 2 3][0]
echo @[echo 1 2 3][1]
echo @[echo 1 2 3][2]

Slice by Range

Slicing by range will take a subsection of an array as a new array:

let array = [ 1 2 3 4 5 ]
echo @array[0..1]
echo @array[0...1]
echo @array[..3]
echo @array[3..]
echo @array[..]


There are two types of methods -- string-based and array-based methods. The type that a method returns is denoted by the sigil that is used to invoke the method. Currently, there are only two supported methods: $join() and @split.

let results = [ 1 2 3 4 5]
echo $join(results) @join # Both of these effectively do the same thing
echo $join(results, ', ') # You may provide a custom pattern instead

let line = "one  two  three  four  five"
echo @split(line) # Splits a line by whitespace

let row = "one,two,three,four,five"
echo @split(row, ',') # Splits by commas

Substring Slicing on String Methods

echo $join(array)[3..6]

Array Slicing on Array Methods

let cpu_model = $(grep "model name" /proc/cpuinfo | head -1)
echo @split(cpu_model)[3..5]


Commands may be written line by line or altogether on the same line with semicolons separating them.

command arg1 arg2 arg3
command arg1 arg2 arg3
command arg1 arg2 arg3; command arg1 arg2 arg3; command arg1 arg2 arg3

Piping & Redirecting Standard Output

The pipe (|) and redirect (>) operators are used for manipulating the standard output.

command arg1 | other_command | another_command arg2
command arg1 > file

Piping & Redirecting Standard Error

The ^| and ^> operators are used for manipulating the standard error.

command arg1 ^| other_command
command arg1 ^> file

Piping & Redirecting Both Standard Output & Standard Error

The &| and &> operators are used for manipulating both the standard output and error.

command arg1 &| other_command # Not supported yet
command arg1 &> file

Conditional Operators

The Ion shell supports the && and || operators in the same manner as the Bash shell. The && operator executes the following command if the previous command exited with a successful exit status. The || operator performs the reverse -- executing if the previous command exited in failure.

test -e .git && echo Git directory exists || echo Git directory does not exist

If Conditions

It is also possible to perform more advanced conditional expressions using the if, else if, and else keywords.

let a = 5;
if test $a -lt 5
    echo "a < 5"
else if test $a -eq 5
    echo "a == 5"
    echo "a > 5"

While Loops

While loops will evaluate a supplied expression for each iteration and execute all the contained statements if it evaluates to a successful exit status.

let a = 1
while test $a -lt 100
    echo $a
    let a += 1

For Loops

For loops, on the other hand, will take a variable followed by a list of values or a range expression, and iterate through all contained statements until all values have been exhausted. If the variable is _, it will be ignored. Take note that quoting rules are reversed for for loops, and values from string-based command substitutions are split by lines.

# Obtaining Values From a Subshell
for a in $(seq 1 10)
    echo $a

# Values Provided Directly
for a in 1 2 3 4 5
    echo $a

# Exclusive Range
for a in 1..11
    echo $a

# Inclusive Range
for a in 1...10
    echo $a

# Ignore Value
for _ in 1..10

# Brace Ranges
for a in {1..10}
    echo $a

# Globbing
for a in *
    echo $a

Command Substitution

Command substitution allows the user to execute commands within a subshell, and have the data written to standard output used as the substitution for the expansion. There are two methods of performing command substitution: string and array-based command substitution. String-based command substitutions are the standard, and they are created by wrapping the external command between $( and ). Array-based command substitution is denoted by wrapping the command between @[ and ]. The first merely captures the result as a single string, precisely as it was written, while the second splits the data recieved into words delimited by whitespaces.

Try comparing the following:

for i in $(echo 1 2 3)
    echo $i
for i in @[echo 1 2 3]
    echo $i

Slicing String-Based Command Substitutions

You may slice the string returned to obtain its substring:

echo $(echo one two three)[..3]

Slicing Array-Based Command Substitutions

You may slice the array returned to obtained a specific set of elements:

echo @[grep "model name" /proc/cpuinfo | head -1][3..5]


Functions in the Ion shell are defined with a name along with a set of variables. The function will check if the correct number of arguments were supplied and execute if all arguments were given.

fn fib n
    if test $n -le 1
        echo $n
        let output = 1
        let previous = 1
        for _ in 2..$n
            let temp = $output
            let output += $previous
            let previous = $temp
        echo $output

for i in 1..20
    fib $i

Executing Scripts with Array Arguments

Arguments supplied to a script are stored in the @args array.

Command executed

script.ion one two three

Script Contents

for argument in @args
    echo $argument