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Oils Reference — Chapter Builtin Commands
This chapter in the Oils Reference describes builtin commands for OSH and YSH.
(in progress)
Append word arguments to a list:
var mylist = :| hello |
append *.py (mylist) # append all Python files
var myflags = []
append -- -c 'echo hi' (myflags) # -- to avoid ambiguity
It's a shortcut for:
call myflags->append('-c')
call myflags->append('echo hi')
Similar names: append
The pp builtin pretty prints values and interpreter state.
Pretty printing expressions is the most common:
$ var x = 42
$ pp (x + 5)
myfile.ysh:1: (Int) 47 # print value with code location
You can pass an unevaluated expression:
$ pp [x + 5]
myfile.ysh:1: (Int) 47 # evaluate first
The value command is a synonym for the interactive = operator:
$ pp value (x)
(Int) 42
$ = x
(Int) 42
Print proc names and doc comments:
$ pp proc # subject to change
You can also print low-level interpreter state. The trailing _ indicates
that the exact format may change:
Examples:
$ var x = :| one two |
$ pp asdl_ (x) # dump the ASDL "guts"
$ pp test_ (x) # single-line stable format, for spec tests
# dump the ASDL representation of a "Cell", which is a location for a value
# (not the value itself)
$ pp cell_ x
The error builtin interrupts shell execution.
If there's a surrounding try block, the _error register is set, and
execution proceeds after the block.
Otherwise, the shell exits with a non-zero status.
Examples:
error 'Missing /tmp' # program fails with status 10
try {
error 'Another problem'
}
echo $[error.code] # => 10
Override the default error code of 10 with a named argument:
error 'Missing /tmp' (code=99) # program fails with status 99
Named arguments add arbitrary properties to the resulting _error register:
error 'Oops' (path='foo.json')
See YSH Error Handling for more examples.
A shortcut for (_error.code !== 0):
try {
ls /tmp
}
if failed {
echo 'ls failed'
}
It saves you 7 punctuation characters: ( _ . !== )
See YSH Error Handling for more examples.
Run a block of code, stopping at the first error. (This is implemented with
shopt --set errexit)
try sets the _error register to a dict, and always returns 0.
try {
ls /nonexistent
}
if (_error.code !== 0) {
echo 'ls failed'
}
Handle expression errors:
try {
var x = 42 / 0
}
And errors from compound commands:
try {
ls | wc -l
diff <(sort left.txt) <(sort right.txt)
}
The case statement can be useful:
try {
grep PATTERN FILE.txt
}
case (_error.code) {
(0) { echo 'found' }
(1) { echo 'not found' }
(else) { echo "grep returned status $[_error.code]" }
}
See YSH Error Handling for more examples.
Runs a command, and requires the exit code to be 0 or 1.
if boolstatus egrep '[0-9]+' myfile { # e.g. aborts on status 2
echo 'found' # status 0 means found
} else {
echo 'not found' # status 1 means not found
}
It's meant for external commands that "return" more than 2 values, like true / false / fail, rather than pass / fail.
Evaluates and expression, and fails if it is not truthy.
assert (false) # fails
assert [false] # also fails (the expression is evaluated)
It's common to pass an unevaluated expression with ===:
func f() { return (42) }
assert [43 === f()]
In this special case, you get a nicer error message:
Expected: 43 Got: 42
That is, the left-hand side should be the expected value, and the right-hand side should be the actual value.
It takes a block:
cd / {
echo $PWD
}
It takes a block:
shopt --unset errexit {
false
echo 'ok'
}
Execute a block with a global variable set.
shvar IFS=/ {
echo "ifs is $IFS"
}
echo "ifs restored to $IFS"
Execute a block with a shared "context" that can be updated using the ctx
built-in.
var mydict = {}
ctx push (mydict) {
# = mydict => {}
ctx set (mykey='myval')
}
# = mydict => { mykey: 'myval' }
The context can be modified with ctx set (key=val), which updates or inserts
the value at the given key.
The context can also be updated with ctx emit field (value).
ctx push (mydict) {
# = mydict => {}
ctx emit mylist (0)
# = mydict => { mylist: [0] }
ctx emit mylist (1)
}
# = mydict => { mylist: [0, 1] }
Contexts can be nested, resulting in a stack of contexts.
ctx push (mydict1) {
ctx set (dict=1)
ctx push (mydict2) {
ctx set (dict=2)
}
}
# = mydict1 => { dict: 1 }
# = mydict2 => { dict: 2 }
ctx is useful for creating DSLs, such as a mini-parseArgs.
proc parser (; place ; ; block_def) {
var p = {}
ctx push (p, block_def)
call place->setValue(p)
}
proc flag (short_name, long_name; type; help) {
ctx emit flag ({short_name, long_name, type, help})
}
proc arg (name) {
ctx emit arg ({name})
}
parser (&spec) {
flag -t --tsv (Bool, help='Output as TSV')
flag -r --recursive (Bool, help='Recurse into the given directory')
flag -N --count (Int, help='Process no more than N files')
arg path
}
Save global registers like $? on a stack. It's useful for preventing plugins from interfering with user code. Example:
status_42 # returns 42 and sets $?
push-registers { # push a new frame
status_43 # top of stack changed here
echo done
} # stack popped
echo $? # 42, read from new top-of-stack
Current list of registers:
Regex data underlying BASH_REMATCH, _group(), _start(), _end()
$?
_error # set by the try builtin
PIPESTATUS # aka _pipeline_status
_process_sub_status
Runs a named proc with the given arguments. It's often useful as the only top level statement in a "task file":
proc p {
echo hi
}
runproc @ARGV
Like 'builtin' and 'command', it affects the lookup of the first word.
Registers a name in the global "module" dict. Returns 0 if it doesn't exist, or 1 if it does.
Use it like this in executable files:
source-guard main || return 0
And like this in libraries:
source-guard myfile.ysh || return 0
The is-main builtin returns 1 (false) if the current file was executed with
the source builtin.
In the "main" file, including -c or stdin input, it returns 0 (true).
Use it like this:
if is-main {
runproc @ARGV
}
TODO
Reuse code from other files, respecting namespaces.
use lib/foo.ysh # foo myproc, $[foo.attr]
# implicit $_this_dir aka relative import
Bind a specific name:
use lib/foo.ysh (&myvar) # makes 'myvar' available
Bind multiple names:
use lib/foo.ysh (&myvar) {
pick log die
}
Maybe:
use lib/foo.ysh (&myvar) {
pick log (&mylog)
pick die (&mydie)
}
Also a declaration
use --extern grep sed
YSH adds long flags to shell's read:
read --all # whole file including trailing \n, fills $_reply
read --all (&x) # fills $x
read --num-bytes 3 # read N bytes, fills _reply
read --num-bytes 3 (&x) # fills $x
read --raw-line # unbuffered read of line, omitting trailing \n
read --raw-line (&x) # fills $x
read --raw-line --with-eol # include the trailing \n
And a convenience:
read -0 # read until NUL, synonym for read -r -d ''
You may want to use fromJson8() or fromJson() after reading a line.
Print arguments to stdout, separated by a space.
ysh$ echo hi there
hi there
The simple_echo option means that flags aren't accepted, and -- is not
accepted.
ysh$ echo -n
-n
See the YSH FAQ for details.
write fixes problems with shell's echo builtin.
The default separator is a newline, and the default terminator is a newline.
Examples:
write -- ale bean # write two lines
write -n -- ale bean # synonym for --end '', like echo -n
write --sep '' --end '' -- a b # write 2 bytes
write --sep $'\t' --end $'\n' -- a b # TSV line
You may want to use toJson8() or toJson() before writing:
write -- $[toJson8(mystr)]
write -- $[toJson(mystr)]
Run a command, but don't wait for it to finish.
fork { sleep 1 }
wait -n
In YSH, use fork rather than shell's & (ampersand).
The preferred alternative to shell's (). Prefer cd with a block if possible.
forkwait {
not_mutated=zzz
}
echo $not_mutated
Runs a block passed to it. It's designed so redirects have a prefix syntax:
fopen >out.txt {
echo 1
echo 2
}
Rather than shell style:
{ echo 1
echo 2
} >out.txt
When a block is long, the former is more readable.
Write JSON:
var d = {name: 'bob', age: 42}
json write (d) # default indentation of 2
json write (d, space=0) # no indentation
Read JSON:
echo hi | json read # fills $_reply by default
Or use an explicit place:
var x = ''
json read (&x) < myfile.txt
Related: err-json-encode and err-json-decode
Like json, but on the encoding side:
b'\yff' instead of lossy Unicode replacement charOn decoding side:
b'' u'' stringsRelated: err-json8-encode and err-json8-decode
TODO: describe
TODO: when
These builtins take input and output. They're often used with redirects.
read FLAG* VAR*
Read a line from stdin, split it into tokens with the $IFS algorithm,
and assign the tokens to the given variables. When no VARs are given,
assign to $REPLY.
Note: When writing ySH, prefer the extensions documented in
ysh-read. The read builtin is confusing because -r needs to
be explicitly enabled.
Flags:
-a ARRAY assign the tokens to elements of this array
-d CHAR use DELIM as delimiter, instead of newline
-n NUM read up to NUM characters, respecting delimiters
-p STR print the string PROMPT before reading input
-r raw mode: don't let backslashes escape characters
-s silent: do not echo input coming from a terminal
-t NUM time out and fail after TIME seconds
-t 0 returns whether any input is available
-u FD read from file descriptor FD instead of 0 (stdin)
echo FLAG* ARG*
Prints ARGs to stdout, separated by a space, and terminated by a newline.
Flags:
-e enable interpretation of backslash escapes
-n omit the trailing newline
See char-escapes.
printf FLAG* FMT ARG*
Formats values and prints them. The FMT string contain three types of objects:
\t. See char-escapes.%s that specify how to format each each ARG.If not enough ARGS are passed, the empty string is used. If too many are passed, the FMT string will be "recycled".
Flags:
-v VAR Write output in variable VAR instead of standard output.
Format specifiers:
%% Prints a single "%".
%b Interprets backslash escapes while printing.
%q Prints the argument escaping the characters needed to make it reusable
as shell input.
%d Print as signed decimal number.
%i Same as %d.
%o Print as unsigned octal number.
%u Print as unsigned decimal number.
%x Print as unsigned hexadecimal number with lower-case hex-digits (a-f).
%X Same as %x, but with upper-case hex-digits (A-F).
%f Print as floating point number.
%e Print as a double number, in "±e" format (lower-case e).
%E Same as %e, but with an upper-case E.
%g Interprets the argument as double, but prints it like %f or %e.
%G Same as %g, but print it like %E.
%c Print as a single char, only the first character is printed.
%s Print as string
%n The number of characters printed so far is stored in the variable named
in the argument.
%a Interprets the argument as double, and prints it like a C99 hexadecimal
floating-point literal.
%A Same as %a, but print it like %E.
%(FORMAT)T Prints date and time, according to FORMAT as a format string
for strftime(3). The argument is the number of seconds since
epoch. It can also be -1 (current time, also the default value
if there is no argument) or -2 (shell startup time).
Alias for mapfile.
mapfile FLAG* ARRAY?
Reads lines from stdin into the variable named ARRAY (default
${MAPFILE[@]}).
Flags:
-t Remove the trailing newline from every line
These builtins accept shell code and run it.
source SCRIPT ARG*
Execute SCRIPT with the given ARGs, in the context of the current shell. That is, existing variables will be modified.
Oils extension: If the SCRIPT starts with ///, we look for scripts embedded in
the oils-for-unix binary. Example:
source ///osh/two.sh # load embedded script
: ${LIB_OSH=fallback/dir}
source $LIB_OSH/two.sh # same thing
The LIB_OSH form is useful for writing a script that works under both bash and OSH.
eval ARG+
Creates a string by joining ARGs with a space, then runs it as a shell command.
Example:
# Create the string echo "hello $name" and run it.
a='echo'
b='"hello $name"'
eval $a $b
Tips:
eval can confuse code and user-supplied data, leading to security
issues.eval.YSH eval:
var myblock = ^(echo hi)
eval (myblock) # => hi
trap FLAG* CMD SIGNAL*
Registers the shell string CMD to be run after the SIGNALs are received. If the CMD is empty, then the signal is ignored.
Flags:
-l Lists all signals and their signal number
-p Prints a list of the installed signal handlers
Tip:
Prefer passing the name of a shell function to trap.
The set and shopt builtins set global shell options. YSH code should use
the more natural shopt.
set FLAG* ARG*
Sets global shell options. Short style:
set -e
Long style:
set -o errexit
Set the arguments array:
set -- 1 2 3
shopt FLAG* OPTION* BLOCK?
Sets global shell options.
Flags:
-s --set Turn the named options on
-u --unset Turn the named options off
-p Print option values
-o Use older set of options, normally controlled by 'set -o'
-q Return 0 if the option is true, else 1
Examples:
shopt --set errexit
You can set or unset multiple options with the groups strict:all,
ysh:upgrade, and ysh:all.
If a block is passed, then the mutated options are pushed onto a stack, the block is executed, and then options are restored to their original state.
These 5 builtins deal with the working directory of the shell.
cd FLAG* DIR
Changes the working directory of the current shell process to DIR.
If DIR isn't specified, change to $HOME. If DIR is -, change to $OLDPWD
(a variable that the sets to the previous working directory.)
Flags:
-L Follow symbolic links, i.e. change to the TARGET of the symlink.
(default).
-P Don't follow symbolic links.
pwd FLAG*
Prints the current working directory.
Flags:
-L Follow symbolic links if present (default)
-P Don't follow symbolic links. Print the link instead of the target.
pushd DIR
Add DIR to the directory stack, then change the working directory to DIR.
Typically used with popd and dirs.
popd
Removes a directory from the directory stack, and changes the working directory
to it. Typically used with pushd and dirs.
dirs FLAG*
Shows the contents of the directory stack. Typically used with pushd and
popd.
Flags:
-c Clear the dir stack.
-l Show the dir stack, but with the real path instead of ~.
-p Show the dir stack, but formatted as one line per entry.
-v Like -p, but numbering each line.
These builtins implement our bash-compatible autocompletion system.
Registers completion policies for different commands.
Generates completion candidates inside a user-defined completion function.
It can also be used in scripts, i.e. outside a completion function.
Changes completion options inside a user-defined completion function.
Adjusts COMP_ARGV according to specified delimiters, and optionally set
variables cur, prev, words (an array), and cword. May also set 'split'.
This is an OSH extension that makes it easier to run the bash-completion project.
Complete an entire shell command string. For example,
compexport -c 'echo $H'
will complete variables like $HOME. And
compexport -c 'ha'
will complete builtins like hay, as well as external commands.
These builtins mutate the state of the shell process.
exec BIN_PATH ARG*
Replaces the running shell with the binary specified, which is passed ARGs. BIN_PATH must exist on the file system; i.e. it can't be a shell builtin or function.
umask MODE?
Sets the bit mask that determines the permissions for new files and directories. The mask is subtracted from 666 for files and 777 for directories.
Oils currently supports writing masks in octal.
If no MODE, show the current mask.
ulimit --all
ulimit -a
ulimit FLAGS* -RESOURCE_FLAG VALUE?
ulimit FLAGS* VALUE? # discouraged
Show and modify process resource limits.
Flags:
-S for soft limit
-H for hard limit
-c -d -f ... # ulimit --all shows all resource flags
Show a table of resources:
ulimit --all
ulimit -a
For example, the table shows that -n is the flag that controls the number
file descriptors, the soft and hard limit for -n, and the multiplication
"factor" for the integer VALUE you pass.
Here are examples of using resource flags.
Get the soft limit for the number of file descriptors:
ulimit -S -n
ulimit -n # same thing
Get the hard limit:
ulimit -H -n
Set the soft or hard limit:
ulimit -S -n 100
ulimit -H -n 100
Set both limits:
ulimit -n 100
A special case that's discouraged: with no resource flag, -f is assumed:
ulimit # equivalent to ulimit -f
ulimit 100 # equivalent to ulimit -f 100
times
Shows the user and system time used by the shell and its child processes.
jobs
Shows all jobs running in the shell and their status.
wait FLAG* ARG
Wait for processes to exit.
If the ARG is a PID, wait only for that job, and return its status.
If there's no ARG, wait for all child processes.
Flags:
-n Wait for the next process to exit, rather than a specific process.
Wait can be interrupted by a signal, in which case the exit code indicates the signal number.
fg JOB?
Returns a job running in the background to the foreground. If no JOB is specified, use the latest job.
test OP ARG
test ARG OP ARG
[ OP ARG ] # [ is an alias for test that requires closing ]
[ ARG OP ARG ]
Evaluates a conditional expression and returns 0 (true) or 1 (false).
Note that [ is the name of a builtin, not an operator in the language. Use 'test' to avoid this confusion.
String expressions:
-n STR True if STR is not empty.
'test STR' is usually equivalent, but discouraged.
-z STR True if STR is empty.
STR1 = STR2 True if the strings are equal.
STR1 != STR2 True if the strings are not equal.
STR1 < STR2 True if STR1 sorts before STR2 lexicographically.
STR1 > STR2 True if STR1 sorts after STR2 lexicographically.
Note: < and > should be quoted like \< and \>
File expressions:
-a FILE Synonym for -e.
-b FILE True if FILE is a block special file.
-c FILE True if FILE is a character special file.
-d FILE True if FILE is a directory.
-e FILE True if FILE exists.
-f FILE True if FILE is a regular file.
-g FILE True if FILE has the sgid bit set.
-G FILE True if current user's group is also FILE's group.
-h FILE True if FILE is a symbolic link.
-L FILE True if FILE is a symbolic link.
-k FILE True if FILE has the sticky bit set.
-O FILE True if current user is the file owner.
-p FILE True if FILE is a named pipe (FIFO).
-r FILE True if FILE is readable.
-s FILE True if FILE has size bigger than 0.
-S FILE True if FILE is a socket file.
-t FD True if file descriptor FD is open and refers to a terminal.
-u FILE True if FILE has suid bit set.
-w FILE True if FILE is writable.
-x FILE True if FILE is executable.
FILE1 -nt FILE2 True if FILE1 is newer than FILE2 (mtime).
FILE1 -ot FILE2 True if FILE1 is older than FILE2 (mtime).
FILE1 -ef FILE2 True if FILE1 is a hard link to FILE2.
Arithmetic expressions coerce arguments to integers, then compare:
INT1 -eq INT2 True if they're equal.
INT1 -ne INT2 True if they're not equal.
INT1 -lt INT2 True if INT1 is less than INT2.
INT1 -le INT2 True if INT1 is less or equal than INT2.
INT1 -gt INT2 True if INT1 is greater than INT2.
INT1 -ge INT2 True if INT1 is greater or equal than INT2.
Other expressions:
-o OPTION True if the shell option OPTION is set.
-v VAR True if the variable VAR is set.
The test builtin also supports POSIX conditionals like -a, -o, !, and ( ), but these are discouraged.
Oils supports these long flags:
--dir same as -d
--exists same as -e
--file same as -f
--symlink same as -L
getopts SPEC VAR ARG*
A single iteration of flag parsing. The SPEC is a sequence of flag characters,
with a trailing : to indicate that the flag takes an argument:
ab # accept -a and -b
xy:z # accept -x, -y arg, and -z
The input is "$@" by default, unless ARGs are passed.
On each iteration, the flag character is stored in VAR. If the flag has an
argument, it's stored in $OPTARG. When an error occurs, VAR is set to ?
and $OPTARG is unset.
Returns 0 if a flag is parsed, or 1 on end of input or another error.
Example:
while getopts "ab:" flag; do
case $flag in
a) flag_a=1 ;;
b) flag_b=$OPTARG" ;;
'?') echo 'Invalid Syntax'; break ;;
esac
done
Notes:
$OPTIND is initialized to 1 every time a shell starts, and is used to
maintain state between invocations of getopts.: and ? can't be flags.Unimplemented.
Usage: help TOPIC?
Examples:
help # this help
help echo # help on the 'echo' builtin
help command-sub # help on command sub $(date)
help oils-usage # identical to oils-for-unix --help
help osh-usage # osh --help
help ysh-usage # ysh --help
hash
Display information about remembered commands.
hash FLAG* CMD+
Determine the locations of commands using $PATH, and remember them.
Flag:
-r Discard all remembered locations.
type FLAG* NAME+
Print the type of each NAME, if it were the first word of a command. Is it a shell keyword, builtin command, shell function, alias, or executable file on $PATH?
Flags:
-a Show all possible candidates, not just the first one
-f Don't search for shell functions
-P Only search for executable files
-t Print a single word: alias, builtin, file, function, or keyword
Similar names: type
Modeled after the bash type
builtin.
command FLAG* CMD ARG*
Look up CMD as a shell builtin or executable file, and execute it with the given ARGs. That is, the lookup ignores shell functions named CMD.
Flags:
-v Instead of executing CMD, print a description of it.
Similar to the 'type' builtin.
builtin CMD ARG*
Look up CMD as a shell builtin, and execute it with the given ARGs. That is, the lookup ignores shell functions and executables named CMD.
alias NAME=CODE
Make NAME a shortcut for executing CODE, e.g. alias hi='echo hello'.
alias NAME
Show the value of this alias.
alias
Show a list of all aliases.
Tips:
Prefer shell functions like:
ls() {
command ls --color "$@"
}
to aliases like:
alias ls='ls --color'
Functions are less likely to cause parsing problems.
\ls or 'ls' disables alias expansionunalias NAME
Remove the alias NAME.
history FLAG*
Display and manipulate the shell's history entries.
history NUM
Show the last NUM history entries.
Flags:
-c Clears the history.
-d POS Deletes the history entry at position POS.
Bash has this, but OSH won't implement it.