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.
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.
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.
ion
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.
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.
ion
let a = one
let b = two
echo $A:$B
echo ${A}s and ${B}s
Ion natively supports splitting supplied strings by graphemes using the same slicing syntax for arrays:
ion
$ let string = "one two three"
$ echo $string[0]
o
$ echo $string[..3]
one
$ echo $string[4..7]
two
$ echo $string[8..]
three
To drop a value from the shell, the drop keyword may be used:
ion
drop git_branch
The let command also supports basic arithmetic.
ion
let a = 1
echo $a
let a += 4
echo $a
let a *= 10
echo $a
let a /= 2
echo $a
let a -= 5
echo $a
The export command works similarly to the let command, but instead of defining a local variable, it defines a
global variable that other processes can access.
ion
export PATH = "~/.cargo/bin:${PATH}"
The export command also supports basic arithmetic.
ion
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.
ion
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.
ion
unalias ls
Brace expansions are used to create permutations of a given input. In addition to simple permutations, Ion supports brace ranges and nested branches.
ion
echo abc{3..1}def{1..3,a..c}
echo ghi{one{a,b,c},two{d,e,f}}
Arrays can be create with the let keyword when the supplied expression evaluates to a vector of values:
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.
ion
let array = [ one two 'three four' ]
One particular use case for arrays is setting command arguments
ion
let lsflags = [ -l -a ]
ls @lsflags
Brace expansions actually create a vector of values under the hood, and thus they can be used to create an array.
ion
let braced_array = {down,up}vote
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.
ion
let word_split_process = @[echo one two three]
Arrays may be called with the @ sigil, which works identical to the variable syntax:
ion
echo @braced_array
echo @{braced_array}
Arrays may also be sliced when an index or index range is supplied:
Slicing by an index will take a string from an array:
```ion 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] ```
Slicing by range will take a subsection of an array as a new array:
ion
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.
```ion 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 ```
ion
echo $join(array)[3..6]
ion
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.
ion
command arg1 arg2 arg3
command arg1 arg2 arg3
command arg1 arg2 arg3; command arg1 arg2 arg3; command arg1 arg2 arg3
The pipe (|) and redirect (>) operators are used for manipulating the standard output.
ion
command arg1 | other_command | another_command arg2
command arg1 > file
The ^| and ^> operators are used for manipulating the standard error.
ion
command arg1 ^| other_command
command arg1 ^> file
The &| and &> operators are used for manipulating both the standard output and error.
ion
command arg1 &| other_command # Not supported yet
command arg1 &> file
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.
ion
test -e .git && echo Git directory exists || echo Git directory does not exist
It is also possible to perform more advanced conditional expressions using the if, else if, and else keywords.
ion
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 will evaluate a supplied expression for each iteration and execute all the contained statements if it evaluates to a successful exit status.
ion
let a = 1
while test $a -lt 100
echo $a
let a += 1
end
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.
```ion
for a in $(seq 1 10) echo $a end
for a in 1 2 3 4 5 echo $a end
for a in 1..11 echo $a end
for a in 1...10 echo $a end
for _ in 1..10 do_something end
for a in {1..10} echo $a end
for a in * echo $a end ```
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:
ion
for i in $(echo 1 2 3)
echo $i
end
ion
for i in @[echo 1 2 3]
echo $i
end
You may slice the string returned to obtain its substring:
ion
echo $(echo one two three)[..3]
You may slice the array returned to obtained a specific set of elements:
ion
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.
```ion 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 ```
Arguments supplied to a script are stored in the @args array.
ion
script.ion one two three
ion
for argument in @args
echo $argument
end
script.ion
one
two
three