+{#add}
+ $num...
Outputs the sum of all arguments, or 0 when there are no arguments.
This command is exactness-preserving.
Examples:
~> + 5 2 7
▶ (num 14)
~> + 1/2 1/3 1/4
▶ (num 13/12)
~> + 1/2 0.5
▶ (num 1.0)
-{#sub}
- $x-num $y-num...
Outputs the result of subtracting from $x-num all the $y-nums, working from left to right. When no $y-
num is given, outputs the negation of $x-num instead (in other words, - $x-num is equivalent to - 0 $x-
num).
This command is exactness-preserving.
Examples:
~> - 5
▶ (num -5)
~> - 5 2
▶ (num 3)
~> - 5 2 7
▶ (num -4)
~> - 1/2 1/3
▶ (num 1/6)
~> - 1/2 0.3
▶ (num 0.2)
~> - 10
▶ (num -10)
*{#mul}
* $num...
Outputs the product of all arguments, or 1 when there are no arguments.
This command is exactness-preserving. Additionally, when any argument is exact 0 and no other argument
is a floating-point infinity, the result is exact 0.
Examples:
~> * 2 5 7
▶ (num 70)
~> * 1/2 0.5
▶ (num 0.25)
~> * 0 0.5
▶ (num 0)
/{#div}
/ $x-num $y-num...
Outputs the result of dividing $x-num with all the $y-nums, working from left to right. When no $y-num
is given, outputs the reciprocal of $x-num instead (in other words, / $y-num is equivalent to / 1 $y-
num).
Dividing by exact 0 raises an exception. Dividing by inexact 0 results with either infinity or NaN ac‐
cording to floating-point semantics.
This command is exactness-preserving. Additionally, when $x-num is exact 0 and no $y-num is exact 0, the
result is exact 0.
Examples:
~> / 2
▶ (num 1/2)
~> / 2.0
▶ (num 0.5)
~> / 10 5
▶ (num 2)
~> / 2 5
▶ (num 2/5)
~> / 2 5 7
▶ (num 2/35)
~> / 0 1.0
▶ (num 0)
~> / 2 0
Exception: bad value: divisor must be number other than exact 0, but is exact 0
[tty 6], line 1: / 2 0
~> / 2 0.0
▶ (num +Inf)
When given no argument, this command is equivalent to cd /, due to the implicit cd feature. (The implic‐
it cd feature will probably change to avoid this oddity).
%{#rem}
% $x $y
Output the remainder after dividing $x by $y. The result has the same sign as $x. Both must be integers
that can represented in a machine word (this limit may be lifted in future).
Examples:
~> % 10 3
▶ 1
~> % -10 3
▶ -1
~> % 10 -3
▶ 1
<<===!=>>={#num-cmp}
< $number... # less
<= $number... # less or equal
== $number... # equal
!= $number... # not equal
> $number... # greater
>= $number... # greater or equal
Number comparisons. All of them accept an arbitrary number of arguments:
1. When given fewer than two arguments, all output $true.
2. When given two arguments, output whether the two arguments satisfy the named relationship.
3. When given more than two arguments, output whether every adjacent pair of numbers satisfy the named
relationship.
Examples:
~> == 3 3.0
▶ $true
~> < 3 4
▶ $true
~> < 3 4 10
▶ $true
~> < 6 9 1
▶ $false
As a consequence of rule 3, the != command outputs $true as long as any adjacent pair of numbers are not
equal, even if some numbers that are not adjacent are equal:
~> != 5 5 4
▶ $false
~> != 5 6 5
▶ $true
<s<=s==s!=s>s>=s{#str-cmp}
<s $string... # less
<=s $string... # less or equal
==s $string... # equal
!=s $string... # not equal
>s $string... # greater
>=s $string... # greater or equal
String comparisons. They behave similarly to their number counterparts when given multiple arguments.
Examples:
~> >s lorem ipsum
▶ $true
~> ==s 1 1.0
▶ $false
~> >s 8 12
▶ $true
all{#all}
all $input-list?
Passes inputs to the output as is. Byte inputs into values, one per line.
This is an identity function for commands with value outputs: a | all is equivalent to a if it only out‐
puts values.
This function is useful for turning inputs into arguments, like:
~> use str
~> put 'lorem,ipsum' | str:split , (all)
▶ lorem
▶ ipsum
Or capturing all inputs in a variable:
~> x = [(all)]
foo
bar
(Press ^D)
~> put $x
▶ [foo bar]
When given a list, it outputs all elements of the list:
~> all [foo bar]
▶ foo
▶ bar
See also one.
assoc{#assoc}
assoc $container $k $v
Output a slightly modified version of $container, such that its value at $k is $v. Applies to both lists
and to maps.
When $container is a list, $k may be a negative index. However, slice is not yet supported.
~> assoc [foo bar quux] 0 lorem
▶ [lorem bar quux]
~> assoc [foo bar quux] -1 ipsum
▶ [foo bar ipsum]
~> assoc [&k=v] k v2
▶ [&k=v2]
~> assoc [&k=v] k2 v2
▶ [&k2=v2 &k=v]
Etymology: Clojure (https://clojuredocs.org/clojure.core/assoc).
See also dissoc.
base{#base}
base $base $number...
Outputs a string for each $number written in $base. The $base must be between 2 and 36, inclusive. Ex‐
amples:
~> base 2 1 3 4 16 255
▶ 1
▶ 11
▶ 100
▶ 10000
▶ 11111111
~> base 16 1 3 4 16 255
▶ 1
▶ 3
▶ 4
▶ 10
▶ ff
bool{#bool}
bool $value
Convert a value to boolean. In Elvish, only $false and errors are booleanly false. Everything else, in‐
cluding 0, empty strings and empty lists, is booleanly true:
~> bool $true
▶ $true
~> bool $false
▶ $false
~> bool $ok
▶ $true
~> bool ?(fail haha)
▶ $false
~> bool ''
▶ $true
~> bool []
▶ $true
~> bool abc
▶ $true
See also not.
break{#break}
Raises the special “break” exception. When raised inside a loop it is captured and causes the loop to
terminate.
Because break raises an exception it can be caught by a try block. If not caught, either implicitly by a
loop or explicitly, it causes a failure like any other uncaught exception.
See the discussion about flow commands and exceptions
Note: You can create a break function and it will shadow the builtin command. If you do so you should
explicitly invoke the builtin. For example:
~> use builtin
~> fn break { put 'break'; builtin:break; put 'should not appear' }
~> for x [a b c] { put $x; break; put 'unexpected' }
▶ a
▶ break
cd{#cd}
cd $dirname
Change directory. This affects the entire process; i.e., all threads whether running indirectly (e.g.,
prompt functions) or started explicitly by commands such as peach.
Note that Elvish’s cd does not support cd -.
See also pwd.
compare{#compare}
compare $a $b
Outputs -1 if $a < $b, 0 if $a = $b, and 1 if $a > $b.
The following comparison algorithm is used:
• Typed numbers are compared numerically. The comparison is consistent with the number comparison com‐
mands, except that NaN values are considered equal to each other and smaller than all other numbers.
• Strings are compared lexicographically by bytes, consistent with the string comparison commands. For
UTF-8 encoded strings, this is equivalent to comparing by codepoints.
• Lists are compared lexicographically by elements, if the elements at the same positions are comparable.
If the ordering between two elements is not defined by the conditions above, i.e. if the value of $a or
$b is not covered by any of the cases above or if they belong to different cases, a “bad value” exception
is thrown.
Examples:
~> compare a b
▶ (num 1)
~> compare b a
▶ (num -1)
~> compare x x
▶ (num 0)
~> compare (float64 10) (float64 1)
▶ (num 1)
Beware that strings that look like numbers are treated as strings, not numbers.
See also order.
constantly{#constantly}
constantly $value...
Output a function that takes no arguments and outputs $values when called. Examples:
~> f=(constantly lorem ipsum)
~> $f
▶ lorem
▶ ipsum
The above example is actually equivalent to simply f = { put lorem ipsum }; it is most useful when the
argument is not a literal value, e.g.
~> f = (constantly (uname))
~> $f
▶ Darwin
~> $f
▶ Darwin
The above code only calls uname once, while if you do f = { put (uname) }, every time you invoke $f, un‐
ame will be called.
Etymology: Clojure (https://clojuredocs.org/clojure.core/constantly).
continue{#continue}
Raises the special “continue” exception. When raised inside a loop it is captured and causes the loop to
begin its next iteration.
Because continue raises an exception it can be caught by a try block. If not caught, either implicitly
by a loop or explicitly, it causes a failure like any other uncaught exception.
See the discussion about flow commands and exceptions
Note: You can create a continue function and it will shadow the builtin command. If you do so you should
explicitly invoke the builtin. For example:
~> use builtin
~> fn continue { put 'continue'; builtin:continue; put 'should not appear' }
~> for x [a b c] { put $x; continue; put 'unexpected' }
▶ a
▶ continue
▶ b
▶ continue
▶ c
▶ continue
count{#count}
count $input-list?
Count the number of inputs.
Examples:
~> count lorem # count bytes in a string
▶ 5
~> count [lorem ipsum]
▶ 2
~> range 100 | count
▶ 100
~> seq 100 | count
▶ 100
deprecate{#deprecate}
deprecate $msg
Shows the given deprecation message to stderr. If called from a function or module, also shows the call
site of the function or import site of the module. Does nothing if the combination of the call site and
the message has been shown before.
~> deprecate msg
deprecation: msg
~> fn f { deprecate msg }
~> f
deprecation: msg
[tty 19], line 1: f
~> exec
~> deprecate msg
deprecation: msg
~> fn f { deprecate msg }
~> f
deprecation: msg
[tty 3], line 1: f
~> f # a different call site; shows deprecate message
deprecation: msg
[tty 4], line 1: f
~> fn g { f }
~> g
deprecation: msg
[tty 5], line 1: fn g { f }
~> g # same call site, no more deprecation message
dir-history{#dir-history}
dir-history
Return a list containing the interactive directory history. Each element is a map with two keys: path
and score. The list is sorted by descending score.
Example:
~> dir-history | take 1
▶ [&path=/Users/foo/.elvish &score=96.79928]
See also edit:command-history.
dissoc{#dissoc}
dissoc $map $k
Output a slightly modified version of $map, with the key $k removed. If $map does not contain $k as a
key, the same map is returned.
~> dissoc [&foo=bar &lorem=ipsum] foo
▶ [&lorem=ipsum]
~> dissoc [&foo=bar &lorem=ipsum] k
▶ [&lorem=ipsum &foo=bar]
See also assoc.
drop{#drop}
drop $n $input-list?
Drop the first $n elements of the input. If $n is larger than the number of input elements, the entire
input is dropped.
Example:
~> drop 2 [a b c d e]
▶ c
▶ d
▶ e
~> use str
~> str:split ' ' 'how are you?' | drop 1
▶ are
▶ 'you?'
~> range 2 | drop 10
Etymology: Haskell.
See also take.
each{#each}
each $f $input-list?
Call $f on all inputs.
An exception raised from break is caught by each, and will cause it to terminate early.
An exception raised from continue is swallowed and can be used to terminate a single iteration early.
Examples:
~> range 5 8 | each {|x| * $x $x }
▶ 25
▶ 36
▶ 49
~> each {|x| put $x[:3] } [lorem ipsum]
▶ lor
▶ ips
See also peach.
Etymology: Various languages, as for each. Happens to have the same name as the iteration construct of
Factor (http://docs.factorcode.org/content/word-each,sequences.html).
eawk{#eawk}
eawk $f $input-list?
For each input, call $f with the input followed by all its fields. A break command will cause eawk to
stop processing inputs. A continue command will exit $f, but is ignored by eawk.
It should behave the same as the following functions:
fn eawk {|f @rest|
each {|line|
@fields = (re:split '[ \t]+'
(re:replace '^[ \t]+|[ \t]+$' '' $line))
$f $line $@fields
} $@rest
}
This command allows you to write code very similar to awk scripts using anonymous functions. Example:
~> echo ' lorem ipsum
1 2' | awk '{ print $1 }'
lorem
1
~> echo ' lorem ipsum
1 2' | eawk {|line a b| put $a }
▶ lorem
▶ 1
echo{#echo}
echo &sep=' ' $value...
Print all arguments, joined by the sep option, and followed by a newline.
Examples:
~> echo Hello elvish
Hello elvish
~> echo "Hello elvish"
Hello elvish
~> echo &sep=, lorem ipsum
lorem,ipsum
Notes: The echo builtin does not treat -e or -n specially. For instance, echo -n just prints -n. Use
double-quoted strings to print special characters, and print to suppress the trailing newline.
See also print.
Etymology: Bourne sh.
eq{#eq}
eq $values...
Determines whether all $values are equal. Writes $true when given no or one argument.
Two values are equal when they have the same type and value.
For complex data structures like lists and maps, comparison is done recursively. A pseudo-map is equal
to another pseudo-map with the same internal type (which is not exposed to Elvish code now) and value.
~> eq a a
▶ $true
~> eq [a] [a]
▶ $true
~> eq [&k=v] [&k=v]
▶ $true
~> eq a [b]
▶ $false
See also is and not-eq.
Etymology: Perl (https://perldoc.perl.org/perlop.html#Equality-Operators).
eval{#eval}
eval $code &ns=$nil &on-end=$nil
Evaluates $code, which should be a string. The evaluation happens in a new, restricted namespace, whose
initial set of variables can be specified by the &ns option. After evaluation completes, the new name‐
space is passed to the callback specified by &on-end if it is not nil.
The namespace specified by &ns is never modified; it will not be affected by the creation or deletion of
variables by $code. However, the values of the variables may be mutated by $code.
If the &ns option is $nil (the default), a temporary namespace built by amalgamating the local and upval‐
ue scopes of the caller is used.
If $code fails to parse or compile, the parse error or compilation error is raised as an exception.
Basic examples that do not modify the namespace or any variable:
~> eval 'put x'
▶ x
~> x = foo
~> eval 'put $x'
▶ foo
~> ns = (ns [&x=bar])
~> eval &ns=$ns 'put $x'
▶ bar
Examples that modify existing variables:
~> y = foo
~> eval 'y = bar'
~> put $y
▶ bar
Examples that creates new variables and uses the callback to access it:
~> eval 'z = lorem'
~> put $z
compilation error: variable $z not found
[ttz 2], line 1: put $z
~> saved-ns = $nil
~> eval &on-end={|ns| saved-ns = $ns } 'z = lorem'
~> put $saved-ns[z]
▶ lorem
exact-num{#exact-num}
exact-num $string-or-number
Coerces the argument to an exact number. If the argument is infinity or NaN, an exception is thrown.
If the argument is a string, it is converted to a typed number first. If the argument is already an ex‐
act number, it is returned as is.
Examples:
~> exact-num (num 0.125)
▶ (num 1/8)
~> exact-num 0.125
▶ (num 1/8)
~> exact-num (num 1)
▶ (num 1)
Beware that seemingly simple fractions that can’t be represented precisely in binary can result in the
denominator being a very large power of 2:
~> exact-num 0.1
▶ (num 3602879701896397/36028797018963968)
exec{#exec}
exec $command? $args...
Replace the Elvish process with an external $command, defaulting to elvish, passing the given arguments.
This decrements $E:SHLVL before starting the new process.
This command always raises an exception on Windows with the message “not supported on Windows”.
exit{#exit}
exit $status?
Exit the Elvish process with $status (defaulting to 0).
external{#external}
external $program
Construct a callable value for the external program $program. Example:
~> x = (external man)
~> $x ls # opens the manpage for ls
See also has-external and search-external.
fail{#fail}
fail $v
Throws an exception; $v may be any type. If $v is already an exception, fail rethrows it.
~> fail bad
Exception: bad
[tty 9], line 1: fail bad
~> put ?(fail bad)
▶ ?(fail bad)
~> fn f { fail bad }
~> fail ?(f)
Exception: bad
Traceback:
[tty 7], line 1:
fn f { fail bad }
[tty 8], line 1:
fail ?(f)
float64{#float64}
float64 $string-or-number
Constructs a floating-point number.
This command is deprecated; use num instead.
from-json{#from-json}
from-json
Takes bytes stdin, parses it as JSON and puts the result on structured stdout. The input can contain
multiple JSONs, and whitespace between them are ignored.
Note that JSON’s only number type corresponds to Elvish’s floating-point number type, and is always con‐
sidered inexact. It may be necessary to coerce JSON numbers to exact numbers using exact-num.
Examples:
~> echo '"a"' | from-json
▶ a
~> echo '["lorem", "ipsum"]' | from-json
▶ [lorem ipsum]
~> echo '{"lorem": "ipsum"}' | from-json
▶ [&lorem=ipsum]
~> # multiple JSONs running together
echo '"a""b"["x"]' | from-json
▶ a
▶ b
▶ [x]
~> # multiple JSONs separated by newlines
echo '"a"
{"k": "v"}' | from-json
▶ a
▶ [&k=v]
See also to-json.
from-lines{#from-lines}
from-lines
Splits byte input into lines, and writes them to the value output. Value input is ignored.
~> { echo a; echo b } | from-lines
▶ a
▶ b
~> { echo a; put b } | from-lines
▶ a
See also from-terminated, read-upto and to-lines.
from-terminated{#from-terminated}
from-terminated $terminator
Splits byte input into lines at each $terminator character, and writes them to the value output. If the
byte input ends with $terminator, it is dropped. Value input is ignored.
The $terminator must be a single ASCII character such as "\x00" (NUL).
~> { echo a; echo b } | from-terminated "\x00"
▶ "a\nb\n"
~> print "a\x00b" | from-terminated "\x00"
▶ a
▶ b
~> print "a\x00b\x00" | from-terminated "\x00"
▶ a
▶ b
See also from-lines, read-upto and to-terminated.
-gc{#-gc}
-gc
Force the Go garbage collector to run.
This is only useful for debug purposes.
get-env{#get-env}
get-env $name
Gets the value of an environment variable. Throws an exception if the environment variable does not ex‐
ist. Examples:
~> get-env LANG
▶ zh_CN.UTF-8
~> get-env NO_SUCH_ENV
Exception: non-existent environment variable
[tty], line 1: get-env NO_SUCH_ENV
See also has-env, set-env and unset-env.
has-env{#has-env}
has-env $name
Test whether an environment variable exists. Examples:
~> has-env PATH
▶ $true
~> has-env NO_SUCH_ENV
▶ $false
See also get-env, set-env and unset-env.
has-external{#has-external}
has-external $command
Test whether $command names a valid external command. Examples (your output might differ):
~> has-external cat
▶ $true
~> has-external lalala
▶ $false
See also external and search-external.
has-key{#has-key}
has-key $container $key
Determine whether $key is a key in $container. A key could be a map key or an index on a list or string.
This includes a range of indexes.
Examples, maps:
~> has-key [&k1=v1 &k2=v2] k1
▶ $true
~> has-key [&k1=v1 &k2=v2] v1
▶ $false
Examples, lists:
~> has-key [v1 v2] 0
▶ $true
~> has-key [v1 v2] 1
▶ $true
~> has-key [v1 v2] 2
▶ $false
~> has-key [v1 v2] 0:2
▶ $true
~> has-key [v1 v2] 0:3
▶ $false
Examples, strings:
~> has-key ab 0
▶ $true
~> has-key ab 1
▶ $true
~> has-key ab 2
▶ $false
~> has-key ab 0:2
▶ $true
~> has-key ab 0:3
▶ $false
has-value{#has-value}
has-value $container $value
Determine whether $value is a value in $container.
Examples, maps:
~> has-value [&k1=v1 &k2=v2] v1
▶ $true
~> has-value [&k1=v1 &k2=v2] k1
▶ $false
Examples, lists:
~> has-value [v1 v2] v1
▶ $true
~> has-value [v1 v2] k1
▶ $false
Examples, strings:
~> has-value ab b
▶ $true
~> has-value ab c
▶ $false
-ifaddrs{#-ifaddrs}
-ifaddrs
Output all IP addresses of the current host.
This should be part of a networking module instead of the builtin module.
is{#is}
is $values...
Determine whether all $values have the same identity. Writes $true when given no or one argument.
The definition of identity is subject to change. Do not rely on its behavior.
~> is a a
▶ $true
~> is a b
▶ $false
~> is [] []
▶ $true
~> is [a] [a]
▶ $false
See also eq.
Etymology: Python (https://docs.python.org/3/reference/expressions.html#is).
keys{#keys}
keys $map
Put all keys of $map on the structured stdout.
Example:
~> keys [&a=foo &b=bar &c=baz]
▶ a
▶ c
▶ b
Note that there is no guaranteed order for the keys of a map.
kind-of{#kind-of}
kind-of $value...
Output the kinds of $values. Example:
~> kind-of lorem [] [&]
▶ string
▶ list
▶ map
The terminology and definition of “kind” is subject to change.
-log{#-log}
-log $filename
Direct internal debug logs to the named file.
This is only useful for debug purposes.
make-map{#make-map}
make-map $input?
Outputs a map from an input consisting of containers with two elements. The first element of each con‐
tainer is used as the key, and the second element is used as the value.
If the same key appears multiple times, the last value is used.
Examples:
~> make-map [[k v]]
▶ [&k=v]
~> make-map [[k v1] [k v2]]
▶ [&k=v2]
~> put [k1 v1] [k2 v2] | make-map
▶ [&k1=v1 &k2=v2]
~> put aA bB | make-map
▶ [&a=A &b=B]
nop{#nop}
nop &any-opt= $value...
Accepts arbitrary arguments and options and does exactly nothing.
Examples:
~> nop
~> nop a b c
~> nop &k=v
Etymology: Various languages, in particular NOP in assembly languages (https://en.wikipedia.org/wi‐
ki/NOP).
not{#not}
not $value
Boolean negation. Examples:
~> not $true
▶ $false
~> not $false
▶ $true
~> not $ok
▶ $false
~> not ?(fail error)
▶ $true
Note: The related logical commands and and or are implemented as special commands instead, since they do
not always evaluate all their arguments. The not command always evaluates its only argument, and is thus
a normal command.
See also bool.
not-eq{#not-eq}
not-eq $values...
Determines whether every adjacent pair of $values are not equal. Note that this does not imply that
$values are all distinct. Examples:
~> not-eq 1 2 3
▶ $true
~> not-eq 1 2 1
▶ $true
~> not-eq 1 1 2
▶ $false
See also eq.
ns{#ns}
ns $map
Constructs a namespace from $map, using the keys as variable names and the values as their values. Exam‐
ples:
~> n = (ns [&name=value])
~> put $n[name]
▶ value
~> n: = (ns [&name=value])
~> put $n:name
▶ value
num{#num}
num $string-or-number
Constructs a typed number.
If the argument is a string, this command outputs the typed number the argument represents, or raises an
exception if the argument is not a valid representation of a number. If the argument is already a typed
number, this command outputs it as is.
This command is usually not needed for working with numbers; see the discussion of numeric commands.
Examples:
~> num 10
▶ (num 10)
~> num 0x10
▶ (num 16)
~> num 1/12
▶ (num 1/12)
~> num 3.14
▶ (num 3.14)
~> num (num 10)
▶ (num 10)
one{#one}
one $input-list?
Passes inputs to outputs, if there is only a single one. Otherwise raises an exception.
This function can be used in a similar way to all, but is a better choice when you expect that there is
exactly one output:
See also all.
only-bytes{#only-bytes}
only-bytes
Passes byte input to output, and discards value inputs.
Example:
~> { put value; echo bytes } | only-bytes
bytes
only-values{#only-values}
only-values
Passes value input to output, and discards byte inputs.
Example:
~> { put value; echo bytes } | only-values
▶ value
order{#order}
order &reverse=$false $less-than=$nil $inputs?
Outputs the input values sorted in ascending order. The sort is guaranteed to be stable
(https://en.wikipedia.org/wiki/Sorting_algorithm#Stability).
The &reverse option, if true, reverses the order of output.
The &less-than option, if given, establishes the ordering of the elements. Its value should be a func‐
tion that takes two arguments and outputs a single boolean indicating whether the first argument is less
than the second argument. If the function throws an exception, order rethrows the exception without out‐
putting any value.
If &less-than has value $nil (the default if not set), it is equivalent to {|a b| eq -1 (compare $a $b)
}.
Examples:
~> put foo bar ipsum | order
▶ bar
▶ foo
▶ ipsum
~> order [(float64 10) (float64 1) (float64 5)]
▶ (float64 1)
▶ (float64 5)
▶ (float64 10)
~> order [[a b] [a] [b b] [a c]]
▶ [a]
▶ [a b]
▶ [a c]
▶ [b b]
~> order &reverse [a c b]
▶ c
▶ b
▶ a
~> order &less-than={|a b| eq $a x } [l x o r x e x m]
▶ x
▶ x
▶ x
▶ l
▶ o
▶ r
▶ e
▶ m
Beware that strings that look like numbers are treated as strings, not numbers. To sort strings as num‐
bers, use an explicit &less-than option:
~> order [5 1 10]
▶ 1
▶ 10
▶ 5
~> order &less-than={|a b| < $a $b } [5 1 10]
▶ 1
▶ 5
▶ 10
See also compare.
peach{#peach}
peach $f $input-list?
Calls $f on all inputs, possibly in parallel.
Like each, an exception raised from break will cause peach to terminate early. However due to the paral‐
lel nature of peach, the exact time of termination is non-deterministic and not even guaranteed.
An exception raised from continue is swallowed and can be used to terminate a single iteration early.
Example (your output will differ):
~> range 1 10 | peach {|x| + $x 10 }
▶ (num 12)
▶ (num 13)
▶ (num 11)
▶ (num 16)
▶ (num 18)
▶ (num 14)
▶ (num 17)
▶ (num 15)
▶ (num 19)
~> range 1 101 |
peach {|x| if (== 50 $x) { break } else { put $x } } |
+ (all) # 1+...+49 = 1225; 1+...+100 = 5050
▶ (num 1328)
This command is intended for homogeneous processing of possibly unbound data. If you need to do a fixed
number of heterogeneous things in parallel, use run-parallel.
See also each and run-parallel.
pprint{#pprint}
pprint $value...
Pretty-print representations of Elvish values. Examples:
~> pprint [foo bar]
[
foo
bar
]
~> pprint [&k1=v1 &k2=v2]
[
&k2=
v2
&k1=
v1
]
The output format is subject to change.
See also repr.
print{#print}
print &sep=' ' $value...
Like echo, just without the newline.
See also echo.
Etymology: Various languages, in particular Perl (https://perldoc.perl.org/functions/print.html) and zsh
(http://zsh.sourceforge.net/Doc/Release/Shell-Builtin-Commands.html), whose prints do not print a trail‐
ing newline.
printf{#printf}
printf $template $value...
Prints values to the byte stream according to a template. If you need to inject the output into the val‐
ue stream use this pattern: printf .... | slurp. That ensures that any newlines in the output of printf
do not cause its output to be broken into multiple values, thus eliminating the newlines, which will oc‐
cur if you do put (printf ....).
Like print, this command does not add an implicit newline; include an explicit "\n" in the formatting
template instead. For example, printf "%.1f\n" (/ 10.0 3).
See Go’s fmt (https://golang.org/pkg/fmt/#hdr-Printing) package for details about the formatting verbs
and the various flags that modify the default behavior, such as padding and justification.
Unlike Go, each formatting verb has a single associated internal type, and accepts any argument that can
reasonably be converted to that type:
• The verbs %s, %q and %v convert the corresponding argument to a string in different ways:
• %s uses to-string to convert a value to string.
• %q uses repr to convert a value to string.
• %v is equivalent to %s, and %#v is equivalent to %q.
• The verb %t first convert the corresponding argument to a boolean using bool, and then uses its Go
counterpart to format the boolean.
• The verbs %b, %c, %d, %o, %O, %x, %X and %U first convert the corresponding argument to an integer us‐
ing an internal algorithm, and use their Go counterparts to format the integer.
• The verbs %e, %E, %f, %F, %g and %G first convert the corresponding argument to a floating-point number
using float64, and then use their Go counterparts to format the number.
The special verb %% prints a literal % and consumes no argument.
Verbs not documented above are not supported.
Examples:
~> printf "%10s %.2f\n" Pi $math:pi
Pi 3.14
~> printf "%-10s %.2f %s\n" Pi $math:pi $math:pi
Pi 3.14 3.141592653589793
~> printf "%d\n" 0b11100111
231
~> printf "%08b\n" 231
11100111
~> printf "list is: %q\n" [foo bar 'foo bar']
list is: [foo bar 'foo bar']
Note: Compared to the POSIX printf command (https://pubs.opengroup.org/on‐
linepubs/007908799/xcu/printf.html) found in other shells, there are 3 key differences:
• The behavior of the formatting verbs are based on Go’s fmt (https://golang.org/pkg/fmt/) package in‐
stead of the POSIX specification.
• The number of arguments after the formatting template must match the number of formatting verbs. The
POSIX command will repeat the template string to consume excess values; this command does not have that
behavior.
• This command does not interpret escape sequences such as \n; just use double-quoted strings.
See also print, echo, pprint and repr.
put{#put}
put $value...
Takes arbitrary arguments and write them to the structured stdout.
Examples:
~> put a
▶ a
~> put lorem ipsum [a b] { ls }
▶ lorem
▶ ipsum
▶ [a b]
▶ <closure 0xc4202607e0>
Note: It is almost never necessary to use put (...) - just write the ... part. For example, put (eq a
b) is the equivalent to just eq a b.
Etymology: Various languages, in particular C (https://manpages.debian.org/stretch/manpages-
dev/puts.3.en.html) and Ruby (https://ruby-doc.org/core-2.2.2/IO.html#method-i-puts) as puts.
rand{#rand}
rand
Output a pseudo-random number in the interval [0, 1). Example:
~> rand
▶ 0.17843564133528436
randint{#randint}
randint $low? $high
Output a pseudo-random integer N such that $low <= N < $high. If not given, $low defaults to 0. Exam‐
ples:
~> # Emulate dice
randint 1 7
▶ 6
range{#range}
range &step $start=0 $end
Outputs numbers, starting from $start and ending before $end, using &step as the increment.
• If $start <= $end, &step defaults to 1, and range outputs values as long as they are smaller than $end.
An exception is thrown if &step is given a negative value.
• If $start > $end, &step defaults to -1, and range outputs values as long as they are greater than $end.
An exception is thrown if &step is given a positive value.
As a special case, if the outputs are floating point numbers, range also terminates if the values stop
changing.
This command is exactness-preserving.
Examples:
~> range 4
▶ (num 0)
▶ (num 1)
▶ (num 2)
▶ (num 3)
~> range 4 0
▶ (num 4)
▶ (num 3)
▶ (num 2)
▶ (num 1)
~> range -3 3 &step=2
▶ (num -3)
▶ (num -1)
▶ (num 1)
~> range 3 -3 &step=-2
▶ (num 3)
▶ (num 1)
▶ (num -1)
~> range (- (math:pow 2 53) 1) +inf
▶ (num 9007199254740991.0)
▶ (num 9007199254740992.0)
When using floating-point numbers, beware that numerical errors can result in an incorrect number of out‐
puts:
~> range 0.9 &step=0.3
▶ (num 0.0)
▶ (num 0.3)
▶ (num 0.6)
▶ (num 0.8999999999999999)
Avoid this problem by using exact rationals:
~> range 9/10 &step=3/10
▶ (num 0)
▶ (num 3/10)
▶ (num 3/5)
Etymology: Python (https://docs.python.org/3/library/functions.html#func-range).
read-line{#read-line}
read-line
Reads a single line from byte input, and writes the line to the value output, stripping the line ending.
A line can end with "\r\n", "\n", or end of file. Examples:
~> print line | read-line
▶ line
~> print "line\n" | read-line
▶ line
~> print "line\r\n" | read-line
▶ line
~> print "line-with-extra-cr\r\r\n" | read-line
▶ "line-with-extra-cr\r"
read-upto{#read-upto}
read-upto $terminator
Reads byte input until $terminator or end-of-file is encountered. It outputs the part of the input read
as a string value. The output contains the trailing $terminator, unless read-upto terminated at end-of-
file.
The $terminator must be a single ASCII character such as "\x00" (NUL).
Examples:
~> echo "a,b,c" | read-upto ","
▶ 'a,'
~> echo "foo\nbar" | read-upto "\n"
▶ "foo\n"
~> echo "a.elv\x00b.elv" | read-upto "\x00"
▶ "a.elv\x00"
~> print "foobar" | read-upto "\n"
▶ foobar
repeat{#repeat}
repeat $n $value
Output $value for $n times. Example:
~> repeat 0 lorem
~> repeat 4 NAN
▶ NAN
▶ NAN
▶ NAN
▶ NAN
Etymology: Clojure (https://clojuredocs.org/clojure.core/repeat).
repr{#repr}
repr $value...
Writes representation of $values, separated by space and followed by a newline. Example:
~> repr [foo 'lorem ipsum'] "aha\n"
[foo 'lorem ipsum'] "aha\n"
See also pprint.
Etymology: Python (https://docs.python.org/3/library/functions.html#repr).
resolve{#resolve}
resolve $command
Output what $command resolves to in symbolic form. Command resolution is described in the language ref‐
erence.
Example:
~> resolve echo
▶ <builtin echo>
~> fn f { }
~> resolve f
▶ <closure 0xc4201c24d0>
~> resolve cat
▶ <external cat>
return{#return}
Raises the special “return” exception. When raised inside a named function (defined by the fn keyword)
it is captured by the function and causes the function to terminate. It is not captured by an ordinary
anonymous function.
Because return raises an exception it can be caught by a try block. If not caught, either implicitly by
a named function or explicitly, it causes a failure like any other uncaught exception.
See the discussion about flow commands and exceptions
Note: If you want to shadow the builtin return function with a local wrapper, do not define it with fn as
fn swallows the special exception raised by return. Consider this example:
~> use builtin
~> fn return { put return; builtin:return }
~> fn test-return { put before; return; put after }
~> test-return
▶ before
▶ return
▶ after
Instead, shadow the function by directly assigning to return~:
~> use builtin
~> var return~ = { put return; builtin:return }
~> fn test-return { put before; return; put after }
~> test-return
▶ before
▶ return
run-parallel{#run-parallel}
run-parallel $callable ...
Run several callables in parallel, and wait for all of them to finish.
If one or more callables throw exceptions, the other callables continue running, and a composite excep‐
tion is thrown when all callables finish execution.
The behavior of run-parallel is consistent with the behavior of pipelines, except that it does not per‐
form any redirections.
Here is an example that lets you pipe the stdout and stderr of a command to two different commands in or‐
der to independently capture the output of each byte stream:
~> fn capture {|f|
var pout = (file:pipe)
var perr = (file:pipe)
var out err
run-parallel {
$f > $pout[w] 2> $perr[w]
file:close $pout[w]
file:close $perr[w]
} {
set out = (slurp < $pout[r])
file:close $pout[r]
} {
set err = (slurp < $perr[r])
file:close $perr[r]
}
put $out $err
}
~> capture { echo stdout-test; echo stderr-test >&2 }
▶ "stdout-test\n"
▶ "stderr-test\n"
This command is intended for doing a fixed number of heterogeneous things in parallel. If you need homo‐
geneous parallel processing of possibly unbound data, use peach instead.
See also peach.
search-external{#search-external}
search-external $command
Output the full path of the external $command. Throws an exception when not found. Example (your output
might vary):
~> search-external cat
▶ /bin/cat
See also external and has-external.
set-env{#set-env}
set-env $name $value
Sets an environment variable to the given value. Example:
~> set-env X foobar
~> put $E:X
▶ foobar
See also get-env, has-env and unset-env.
show{#show}
show $e
Shows the value to the output, which is assumed to be a VT-100-compatible terminal.
Currently, the only type of value that can be showed is exceptions, but this will likely expand in fu‐
ture.
Example:
~> e = ?(fail lorem-ipsum)
~> show $e
Exception: lorem-ipsum
[tty 3], line 1: e = ?(fail lorem-ipsum)
sleep{#sleep}
sleep $duration
Pauses for at least the specified duration. The actual pause duration depends on the system.
This only affects the current Elvish context. It does not affect any other contexts that might be exe‐
cuting in parallel as a consequence of a command such as peach.
A duration can be a simple number (with optional fractional value) without an explicit unit suffix, with
an implicit unit of seconds.
A duration can also be a string written as a sequence of decimal numbers, each with optional fraction,
plus a unit suffix. For example, “300ms”, “1.5h” or “1h45m7s”. Valid time units are “ns”, “us” (or
“µs”), “ms”, “s”, “m”, “h”.
Passing a negative duration causes an exception; this is different from the typical BSD or GNU sleep com‐
mand that silently exits with a success status without pausing when given a negative duration.
See the Go documentation (https://golang.org/pkg/time/#ParseDuration) for more information about how du‐
rations are parsed.
Examples:
~> sleep 0.1 # sleeps 0.1 seconds
~> sleep 100ms # sleeps 0.1 seconds
~> sleep 1.5m # sleeps 1.5 minutes
~> sleep 1m30s # sleeps 1.5 minutes
~> sleep -1
Exception: sleep duration must be >= zero
[tty 8], line 1: sleep -1
slurp{#slurp}
slurp
Reads bytes input into a single string, and put this string on structured stdout.
Example:
~> echo "a\nb" | slurp
▶ "a\nb\n"
Etymology: Perl, as File::Slurp (http://search.cpan.org/~uri/File-Slurp-9999.19/lib/File/Slurp.pm).
src{#src}
src
Output a map-like value describing the current source being evaluated. The value contains the following
fields:
• name, a unique name of the current source. If the source originates from a file, it is the full path
of the file.
• code, the full body of the current source.
• is-file, whether the source originates from a file.
Examples:
~> put (src)[name code is-file]
▶ '[tty]'
▶ 'put (src)[name code is-file]'
▶ $false
~> echo 'put (src)[name code is-file]' > show-src.elv
~> elvish show-src.elv
▶ /home/elf/show-src.elv
▶ "put (src)[name code is-file]\n"
▶ $true
Note: this builtin always returns information of the source of the function calling src. Consider the
following example:
~> echo 'fn show { put (src)[name] }' > ~/.elvish/lib/src-fsutil.elv
~> use src-util
~> src-util:show
▶ /home/elf/.elvish/lib/src-fsutil.elv
-stack{#-stack}
-stack
Print a stack trace.
This is only useful for debug purposes.
styled{#styled}
styled $object $style-transformer...
Construct a styled text by applying the supplied transformers to the supplied object. $object can be ei‐
ther a string, a styled segment (see below), a styled text or an arbitrary concatenation of them. A
$style-transformer is either:
• The name of a builtin style transformer, which may be one of the following:
• One of the attribute names bold, dim, italic, underlined, blink or inverse for setting the corre‐
sponding attribute.
• An attribute name prefixed by no- for unsetting the attribute.
• An attribute name prefixed by toggle- for toggling the attribute between set and unset.
• A color name for setting the text color, which may be one of the following:
• One of the 8 basic ANSI colors: black, red, green, yellow, blue, magenta, cyan and white.
• The bright variant of the 8 basic ANSI colors, with a bright- prefix.
• Any color from the xterm 256-color palette, as colorX (such as color12).
• A 24-bit RGB color written as #RRGGBB such as '#778899'.
Note: You need to quote such values since an unquoted # char introduces a comment. So use
'bg-#778899' not bg-#778899. If you omit the quotes the text after the # char is ignored which will
result in an error or unexpected behavior.
• A color name prefixed by bg- to set the background color.
• A color name prefixed by fg- to set the foreground color. This has the same effect as specifying the
color name without the fg- prefix.
• A lambda that receives a styled segment as the only argument and returns a single styled segment.
• A function with the same properties as the lambda (provided via the $transformer~ syntax).
When a styled text is converted to a string the corresponding ANSI SGR code (https://en.wikipedia.org/wi‐
ki/ANSI_escape_code#SGR_.28Select_Graphic_Rendition.29_parameters) is built to render the style.
A styled text is nothing more than a wrapper around a list of styled segments. They can be accessed by
indexing into it.
s = (styled abc red)(styled def green)
put $s[0] $s[1]
styled-segment{#styled-segment}
styled-segment $object &fg-color=default &bg-color=default &bold=$false &dim=$false &italic=$false &underlined=$false &blink=$false &inverse=$false
Constructs a styled segment and is a helper function for styled transformers. $object can be a plain
string, a styled segment or a concatenation thereof. Probably the only reason to use it is to build cus‐
tom style transformers:
fn my-awesome-style-transformer {|seg| styled-segment $seg &bold=(not $seg[dim]) &dim=(not $seg[italic]) &italic=$seg[bold] }
styled abc $my-awesome-style-transformer~
As just seen the properties of styled segments can be inspected by indexing into it. Valid indices are
the same as the options to styled-segment plus text.
s = (styled-segment abc &bold)
put $s[text]
put $s[fg-color]
put $s[bold]
take{#take}
take $n $input-list?
Retain the first $n input elements. If $n is larger than the number of input elements, the entire input
is retained. Examples:
~> take 3 [a b c d e]
▶ a
▶ b
▶ c
~> use str
~> str:split ' ' 'how are you?' | take 1
▶ how
~> range 2 | take 10
▶ 0
▶ 1
Etymology: Haskell.
tilde-abbr{#tilde-abbr}
tilde-abbr $path
If $path represents a path under the home directory, replace the home directory with ~. Examples:
~> echo $E:HOME
/Users/foo
~> tilde-abbr /Users/foo
▶ '~'
~> tilde-abbr /Users/foobar
▶ /Users/foobar
~> tilde-abbr /Users/foo/a/b
▶ '~/a/b'
time{#time}
time &on-end=$nil $callable
Runs the callable, and call $on-end with the duration it took, as a number in seconds. If $on-end is
$nil (the default), prints the duration in human-readable form.
If $callable throws an exception, the exception is propagated after the on-end or default printing is
done.
If $on-end throws an exception, it is propagated, unless $callable has already thrown an exception.
Example:
~> time { sleep 1 }
1.006060647s
~> time { sleep 0.01 }
1.288977ms
~> t = ''
~> time &on-end={|x| t = $x } { sleep 1 }
~> put $t
▶ (float64 1.000925004)
~> time &on-end={|x| t = $x } { sleep 0.01 }
~> put $t
▶ (float64 0.011030208)
to-json{#to-json}
to-json
Takes structured stdin, convert it to JSON and puts the result on bytes stdout.
~> put a | to-json
"a"
~> put [lorem ipsum] | to-json
["lorem","ipsum"]
~> put [&lorem=ipsum] | to-json
{"lorem":"ipsum"}
See also from-json.
to-lines{#to-lines}
to-lines $input?
Writes each value input to a separate line in the byte output. Byte input is ignored.
~> put a b | to-lines
a
b
~> to-lines [a b]
a
b
~> { put a; echo b } | to-lines
b
a
See also from-lines and to-terminated.
to-string{#to-string}
to-string $value...
Convert arguments to string values.
~> to-string foo [a] [&k=v]
▶ foo
▶ '[a]'
▶ '[&k=v]'
to-terminated{#to-terminated}
to-terminated $terminator $input?
Writes each value input to the byte output with the specified terminator character. Byte input is ig‐
nored. This behavior is useful, for example, when feeding output into a program that accepts NUL termi‐
nated lines to avoid ambiguities if the values contains newline characters.
The $terminator must be a single ASCII character such as "\x00" (NUL).
~> put a b | to-terminated "\x00" | slurp
▶ "a\x00b\x00"
~> to-terminated "\x00" [a b] | slurp
▶ "a\x00b\x00"
See also from-terminated and to-lines.
unset-env{#unset-env}
unset-env $name
Unset an environment variable. Example:
~> E:X = foo
~> unset-env X
~> has-env X
▶ $false
~> put $E:X
▶ ''
See also has-env, get-env and set-env.
use-mod{#use-mod}
use-mod $use-spec
Imports a module, and outputs the namespace for the module.
Most code should use the use special command instead.
Examples:
~> echo 'x = value' > a.elv
~> put (use-mod ./a)[x]
▶ value
wcswidth{#wcswidth}
wcswidth $string
Output the width of $string when displayed on the terminal. Examples:
~> wcswidth a
▶ 1
~> wcswidth lorem
▶ 5
~> wcswidth 你好，世界
▶ 10
Elvish 0.17.0 Nov 18, 2024 elvish-builtin(7)
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