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Oils Reference — Chapter Types and Methods
This chapter describes YSH types and methods. There are also two OSH types for bash compatibility.
(in progress)
These two types are for OSH code only.
A bash array holds a sequence of strings. Some entries may be unset, i.e. not an empty string.
See sh-array for details. In YSH, prefer to use List instances.
A bash associative array is a mapping from strings to strings.
See sh-assoc for details. In YSH, prefer to use Dict instances.
An Obj instance representing the Null type.
The Null type has a single value spelled null. (Related:
atom-literal).
A value that's not equal to any other. Values that aren't explicitly
initialized are null, e.g.
var x
= x # => (Null) null
Its type is Null.
An Obj instance representing the boolean type.
This type has 2 values: true and false. (Related: atom-literal).
A single value representing truth, e.g.
= 42 === 42 # => true
A single value representing the opposite of truth, e.g.
= 42 === 3 # => false
Integers are currently 64-bit signed integers (on all platforms). TODO: they should be arbitrary precision.
There are many way of writing integers; see int-literal.
In shell, ASCII strings like '42' are often used for calculations on
integers. But you can use a "real" integer type in YSH.
YSH has 64-bit floating point numbers. See float-literal for how to denote them.
A Range is a pair of two numbers, used for iteration. See range for how
to denote them.
Ranges are used for iteration; see ysh-for.
In Oils, strings may contains any sequence of bytes, which may be UTF-8 encoded.
Internal NUL bytes (0x00) are allowed.
When passing such strings to say the cd builtin, the string will be
truncated before the NUL. This is because most C functions like chdir() take
NUL-terminated strings.
An Obj instance representing the string type.
TODO:
var i = mystr.find('foo')
Similar to
= 'foo' in mystr
Both of them do substring search.
Also similar to mystr.search(eggex).
Replace substrings with a given string.
= mystr => replace("OSH", "YSH")
Or match with an Eggex.
= mystr => replace(/ d+ /, "<redacted>") # => "code is <redacted>"
Refer to Eggex captures with replacement expressions. Captured values can be
referenced with $1, $2, etc.
var mystr = "1989-06-08"
var pat = / <capture d{4}> '-' <capture d{2}> '-' <capture d{2}> /
= mystr => replace(pat, ^"Year: $1, Month: $2, Day: $3")
Captures can also be named.
= mystr2 => replace(/ <capture digit{4} as year : int> /, ^"$[year + 1]")
$0 refers to the entire capture itself in a substitution string.
var mystr = "replace with mystr => replace()"
= mystr => replace(/ alpha+ '=>' alpha+ '()' /, ^"<code>$0</code>")
# => "replace with <code>mystr => replace()</code>"
In addition to captures, other variables can be referenced within a replacement expression.
= mystr => replace(/ <capture alpha+> /, ^"$1 and $anotherVar")
To limit the number of replacements, pass in a named count argument. By default
the count is -1. For any count in [0, MAX_INT], there will be at most count
replacements. Any negative count means "replace all" (ie. count=-2 behaves
exactly like count=-1).
var mystr = "bob has a friend named bob"
= mystr => replace("bob", "Bob", count=1) # => "Bob has a friend named bob"
= mystr => replace("bob", "Bob", count=-1) # => "Bob has a friend named Bob"
The following matrix of signatures are supported by replace():
s => replace(string_val, subst_str)
s => replace(string_val, subst_expr)
s => replace(eggex_val, subst_str)
s => replace(eggex_val, subst_expr)
Replacing by an Eggex has some limitations:
search() results in an empty string match, eg.
'abc'.split(/ space* /), then we raise an error to avoid an infinite loop.Checks if a string starts with a pattern, returning true if it does or false if it does not.
= b'YSH123' => startsWith(b'YSH') # => true
= b'123YSH' => startsWith(b'YSH') # => false
= b'123YSH' => startsWith(/ d+ /) # => true
= b'YSH123' => startsWith(/ d+ /) # => false
Matching is done based on bytes, not runes.
= b'\yce\ya3' # => (Str) "Σ"
= 'Σ' => startsWith(b'\yce') # => true
= 'Σ' => endsWith(b'\ya3') # => true
Like startsWith() but returns true if the end of the string matches.
= b'123YSH' => endsWith("YSH") # => true
= b'YSH123' => endsWith(/ d+ /) # => true
Removes characters matching a pattern from the start and end of a string. With no arguments, whitespace is removed. When given a string or eggex pattern, that pattern is removed if it matches the start or end.
= b' YSH\n' => trim() # => "YSH"
= b'xxxYSHxxx' => trim('xxx') # => "YSH"
= b'xxxYSH ' => trim('xxx') # => "YSH "
= b' YSHxxx' => trim('xxx') # => " YSH"
= b' YSH ' => trim('xxx') # => " YSH "
= b'123YSH456' => trim(/ d+ /) # => "YSH"
When stripping whitespace, Oils decodes the bytes in string as utf-8 characters. Only the following Unicode codepoints are considered to be whitespace.
\t)\n)\v)\f)\r)<NBSP><ZWNBSP>While the Unicode standard defines other codepoints as being spaces, Oils limits itself to just these codepoints so that the specification is stable, and doesn't depend on an external standard that has reclassify characters.
Like trim() but only removes characters from the start of the string.
= b' YSH\n' => trimStart() # => "YSH\n"
= b'xxxYSHxxx' => trimStart(b'xxx') # => "YSHxxx"
= b'123YSH456' => trimStart(/ d+ /) # => "YSH456"
Like trim() but only removes characters from the end of the string.
= b' YSH\n' => trimEnd() # => " YSH"
= b'xxxYSHxxx' => trimEnd(b'xxx') # => "YxxxSH"
= b'123YSH456' => trimEnd(/ d+ /) # => "123YSH"
Respects unicode.
Respects unicode.
Search for the first occurrence of a regex in the string.
var m = 'hi world' => search(/[aeiou]/) # search for vowels
# matches at position 1 for 'i'
Returns a value.Match() if it matches, otherwise null.
You can start searching in the middle of the string:
var m = 'hi world' => search(/dot 'orld'/, pos=3)
# also matches at position 4 for 'o'
The %start or ^ metacharacter will only match when pos is zero.
(Similar to Python's re.search().)
leftMatch() is like search(), but it checks
var m = 'hi world' => leftMatch(/[aeiou]/) # search for vowels
# doesn't match because h is not a vowel
var m = 'aye' => leftMatch(/[aeiou]/)
# matches 'a'
leftMatch() Can be used to implement lexers that consume every byte of input.
var lexer = / <capture digit+> | <capture space+> /
(Similar to Python's re.match().)
Split a string by a Str separator sep into a List of chunks.
pp ('a;b;;c'.split(';')) # => ["a", "b", "", "c"]
pp ('a<>b<>c<d'.split('<>')) # => ["a", "b", "c<d"]
pp ('🌞🌝🌞🌝🌞'.split('🌝')) # => ["🌞", "🌞", "🌞"]
Or split using an Eggex.
pp ('a b cd'.split(/ space+ /)) # => ["a", "b", "cd"]
pp ('a,b;c'.split(/ ',' | ';' /)) # => ["a", "b", "c"]
Optionally, provide a count to split on sep at most count times. A
negative count will split on all occurrences of sep.
pp ('a;b;;c'.split(';', count=2)) # => ["a", "b", ";c"]
pp ('a;b;;c'.split(';', count=-1)) # => ["a", "b", "", "c"]
Passing an empty sep will result in an error.
pp ('abc'.split('')) # => Error: Sep cannot be ""
Splitting by an Eggex has some limitations:
search() results in an empty string match, eg.
'abc'.split(/ space* /), then we raise an error to avoid an infinite loop.An Eggex is a composable regular expression. It can be spliced into other
regular expressions.
A Match is the result searching for an Eggex within a Str.
Returns the string that matched a regex capture group. Group 0 is the entire match.
var m = '10:59' => search(/ ':' <capture d+> /)
echo $[m => group(0)] # => ':59'
echo $[m => group(1)] # => '59'
Matches can be named with as NAME:
var m = '10:59' => search(/ ':' <capture d+ as minute> /)
And then accessed by the same name:
echo $[m => group('minute')] # => '59'
Like group(), but returns the start position of a regex capture group,
rather than its value.
var m = '10:59' => search(/ ':' <capture d+ as minute> /)
echo $[m => start(0)] # => position 2 for ':59'
echo $[m => start(1)] # => position 3 for '59'
echo $[m => start('minute')] # => position 3 for '59'
Like group(), but returns the end position of a regex capture group,
rather than its value.
var m = '10:59' => search(/ ':' <capture d+ as minute> /)
echo $[m => end(0)] # => position 5 for ':59'
echo $[m => end(1)] # => position 5 for '59'
echo $[m => end('minute')] # => 5 for '59'
An Obj instance representing the List type.
A List contains an ordered sequence of values.
Add an element to a list.
var fruits = :|apple banana pear|
call fruits->append("orange")
echo @fruits # => apple banana pear orange
Similar names: append
remove an element from a list and return it.
var fruits = :|apple banana pear orange|
var last = fruits->pop() # "orange" is removed AND returned
echo $last # => orange
echo @fruits # => apple banana pear
Extend an existing list with the elements of another list.
var foods = :|cheese chocolate|
var fruits = :|apple banana|
call foods->extend(fruits)
echo @foods # => cheese chocolate apple banana
Returns the first index of the element in the list, or -1 if it's not present.
var names = :| Jane Peter Joana Sam |
echo $[names => indexOf("Sam")] # => 3
echo $[names => indexOf("Simon")] # => -1
Reverses a list in place.
var fruits = :|apple banana pear|
call fruits->reverse()
echo @fruits # => pear banana apple
TODO:
Remove all entries from the List:
call mylist->clear()
An Obj instance representing the Dict type.
A Dict contains an ordered sequence of key-value pairs. Given the key, the value can be retrieved efficiently.
Ensures that the given key does not exist in the dictionary.
var book = {
title: "The Histories",
author: "Herodotus",
}
= book
# => (Dict) {title: "The Histories", author: "Herodotus"}
call book->erase("author")
= book
# => (Dict) {title: "The Histories"}
# repeating the erase call does not cause an error
call book->erase("author")
= book
# => (Dict) {title: "The Histories"}
TODO:
call mydict->accum('key', 'string to append')
Similar:
setvar mydict['k'] += 3 # TODO: default value of 0
TODO:
Remove all entries from the Dict:
call mydict->clear()
A Place is used as an "out param" by calling setValue():
proc p (out) {
call out->setValue('hi')
}
var x
p (&x)
echo x=$x # => x=hi
User-defined functions.
A func that's part of Oils, like len().
The thin-arrow and fat-arrow create bound funcs:
var bound = '' => upper
var bound2 = [] -> append
User-defined procs.
A builtin proc, aka builtin command, like module-invoke.
An instance of Obj, representing the Obj type.
TODO: make it callable.
__invoke__The __invoke__ meta-method makes an Object "proc-like".
First, define a proc, with the first typed arg named self:
proc myInvoke (word_param; self, int_param) {
echo "sum = $[self.x + self.y + int_param]"
}
Make it the __invoke__ method of an Obj:
var methods = Object(null, {__invoke__: myInvoke})
var invokable_obj = Object(methods, {x: 1, y: 2})
Then invoke it like a proc:
invokable_obj myword (3)
# sum => 6
Create an object:
var methods = Obj.new({mymethod: foo}, null)
var instance = Obj.new({x: 3, y: 4}, methods)
TODO: This will become Obj.__call__, which means it's written Obj.
__call__TODO
__index__The __index__ meta-method controls what happens when obj[x] is evaluated.
It's currently used for type objects:
var t = Dict[Str, Int]
assert [t is Dict[Str, Int]] # always evaluates to the same instance
__str__TODO
An unevaluated command. You can create a Command with a "block expression"
(block-expr):
var block = ^(echo $PWD; ls *.txt)
The Command is bound to a stack frame. This frame will be pushed as an "enclosed frame" when the command is evaluated.
A command that's not bound to a stack frame.
An unevaluated expression. You can create an Expr with an expression literal
(expr-literal):
var expr = ^[42 + a[i]]
The Command is bound to a stack frame. This frame will be pushed as an "enclosed frame" when the expression is evaluated.
A value that represents a stack frame. It can be bound to a CommandFrag,
producing a Command.
Likewise, it can be found to a ExprFrag, producing an Expr.
Returns the singleton stdin value, which you can iterate over:
for line in (io.stdin) {
echo $line
}
This is buffered line-based I/O, as opposed to the unbuffered I/O of the read
builtin.
Given an Expr value, evaluate it and return its value:
$ var i = 42
$ var expr = ^[i + 1]
$ = io->evalExpr(expr)
43
Examples of expressions that have effects:
^[ myplace->setValue(42) ] - memory operation^[ $(echo 42 > hi) ] - I/O operationEvaluate a command, and return null.
var cmd = ^(echo hi)
call io->eval(cmd)
It's similar to the eval builtin, and is meant to be used in pure functions.
You can also bind:
$1 $2 $3$0Examples:
var cmd = ^(echo "zero $0, one $1, named $x")
call io->eval(cmd, dollar0="z", pos_args=['one'], vars={x: "x"})
# => zero z, one one, named x
The evalToDict() method is like the eval() method, but it returns a
Dict of bindings.
It pushes a new "enclosed frame", and executes the given code.
Then it copies the frame's bindings into a Dict, and returns it. Only the
names that don't end with an underscore _ are copied.
Example:
var x = 10 # captured
var cmd = ^(var a = 42; var hidden_ = 'h'; var b = x + 1)
var d = io->evalToDict(cmd)
pp (d) # => {a: 42, b: 11}
Capture stdout of a command a string.
var c = ^(echo hi)
var stdout_str = _io.captureStdout(c) # => "hi"
It's like $(), but useful in pure functions. Trailing newlines \n are
removed.
If the command fails, captureStdout() raises an error, which can be caught
with try.
try {
var s = _io->captureStdout(c)
}
An API the wraps the $PS1 language. For example, to simulate PS1='\w\$ ':
func renderPrompt(io) {
var parts = []
call parts->append(io.promptval('w')) # pass 'w' for \w
call parts->append(io.promptval('$')) # pass '$' for \$
call parts->append(' ')
return (join(parts))
}
TODO: Depends on system clock.
TODO: Like the awk function, this takes an timestamp directly.
In other words, it calls C localtime() (which depends on the time zone database), and then C strftime().
TODO: The free function glob() actually does I/O. Although maybe it doesn't fail?
An object with functions for introspecting the Oils VM.
Given an index, get a handle to a call stack frame.
var frame = vm.getFrame(0) # global frame
var frame = vm.getFrame(1) # first frame pushed on the global frame
var frame = vm.getFrame(-1) # the current frame, aka local frame
var frame = vm.getFrame(-2) # the calling frame
If the index is out of range, an error is raised.
Returns an integer ID for mutable values like List, Dict, and Obj.
= vm.id({})
(Int) 123
You can use it to test if two names refer to the same instance.
vm.id() is undefined on immutable values like Bool, Int, Float, Str, etc.