README.md

Ion Shell

Ion is the underlying library for shells and command execution in Redox, as well as the default shell.

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.

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

Export

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

Aliases

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

Commands

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 # Not supported yet
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"
else
    echo "a > 5"
end

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
end

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.

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

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

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

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

# Ignore Value
for _ in 1..10
   do_something
end

Functions

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

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

for i in 1..20
    fib $i
end

Brace Expansion

It is possible to perform brace expansions within the Ion shell. Currently, only permutation braces are supported.

echo abc{1,2,3}def{456,789,101112}