source | all docs for version 0.8.4 | all versions | oilshell.org
Warning: Work in progress! Leave feedback on Zulip or Github if you'd like this doc to be updated.
This doc describes every aspect of OSH briefly. It underlies the help
builtin, and is indexed by keywords.
Navigate it with the index of OSH help topics.
bin/osh UsageUsage: osh [OPTION]... SCRIPT [ARG]...
osh [OPTION]... -c COMMAND [ARG]...
The command line accepted by bin/osh is compatible with /bin/sh and bash.
osh -c 'echo hi'
osh myscript.sh
echo 'echo hi' | osh
It also has a few enhancements:
osh -n -c 'hello' # pretty-print the AST
osh --ast-format text -n -c 'hello' # print it full
osh accepts POSIX sh flags, with these additions:
-n parse the program but don't execute it. Print the AST. --ast-format what format the AST should be in
If the --rcfile flag is specified, that file will be executed on startup. Otherwise:
bin/osh runs ~/.config/oil/oshrcbin/oil runs ~/.config/oil/oilrcPass --rcfile /dev/null to disable this behavior.
History is read?
A comment starts with # and goes until the end of the line.
echo hi # print a greeting
A backslash \ at the end of a line continues the line without executing it:
ls /usr/bin \
/usr/lib \
~/src # A single command split over three lines
Commands are composed of words. The first word may by the name of a shell builtin, an Oil proc / shell "function", an external command, or an alias:
echo hi # a shell builtin doesn't start a process
ls /usr/bin ~/src # starts a new process
myproc "hello $name"
myshellfunc "hello $name"
myalias -l
Redirects are also allowed in any part of the command:
echo 'to stderr' >&2
echo >&2 'to stderr'
echo 'to file' > out.txt
echo > out.txt 'to file'
Run two commands in sequence like this:
echo one; echo two
or this:
echo one
echo two
Match a string against a series of glob patterns. Execute code in the section below the matching pattern.
path='foo.py'
case "$path" in
*.py)
echo 'python'
;;
*.sh)
echo 'shell'
;;
esac
Test if a command exited with status zero (true). If so, execute the corresponding block of code.
Shell:
if test -d foo; then
echo 'foo is a directory'
elif test -f foo; then
echo 'foo is a file'
else
echo 'neither'
fi
Oil:
if test -d foo {
echo 'foo is a directory'
} elif test -f foo {
echo 'foo is a file'
} else {
echo 'neither'
}
Do nothing and return status 0.
if true; then
echo hello
fi
Do nothing and return status 1.
if false; then
echo 'not reached'
else
echo hello
fi
Like true: do nothing and return status 0.
Invert an exit code:
if ! test -d /tmp; then
echo "No temp directory
fi
mkdir -p /tmp && cp foo /tmp
ls || die "failed"
POSIX
POSIX
For loops iterate over words.
Oil style:
var mystr = 'one'
var myarray = %(two three)
for i in $mystr @myarray *.py {
echo $i
}
Shell style:
local mystr='one'
local myarray=(two three)
for i in "mystr" "${myarray[@]}" *.py; do
echo $i
done
Both fragments output 3 lines and then Python files on remaining lines.
A bash/ksh construct:
for (( i = 0; i < 5; ++i )); do
echo $i
done
These are keywords in Oil, not builtins!
Break out of a loop. (Not used for case statements!)
Continue to the next iteration of a loop.
Return from a function.
Exit the shell process with the given status:
exit 2
POSIX:
f() {
echo args "$@"
}
f 1 2 3
POSIX:
{ echo one; echo two; }
Note the trailing ; -- which isn't necessary in Oil.
( echo one; echo two )
Use forkwait in Oil instead.
CMD &
The & language construct runs CMD in the background as a job, immediately
returning control to the shell.
The resulting PID is recorded in the $! variable.
Three variants of redirecting stdout:
echo foo > out.txt # write to a file
echo foo >> out.txt # append to a file
echo foo >| out.txt # clobber the file even if set -o noclobber
Redirect stdin:
cat < in.txt
Redirect to a file descriptor:
echo 'to stderr' >&2
TODO: unbalanced HTML if we use <<?
cat <<EOF
here doc with $double ${quoted} substitution
EOF
myfunc() {
cat <<-EOF
here doc with one tab leading tab stripped
EOF
}
cat <<< 'here string'
time [-p] pipeline
Measures the time taken by a command / pipeline. It uses the getrusage()
function from libc.
Note that time is a KEYWORD, not a builtin!
Array literals in shell accept any sequence of words, just like a command does:
ls $mystr "$@" *.py
# Put it in an array
a=(ls $mystr "$@" *.py)
In Oil, use oil-array.
In Oil, use oil-dict.
Alias for declare.
$'\n'Also see oil-string.
Evaluates to the stdout of a command. If a trailing newline is returned, it's stripped:
$ hostname
example.com
$ x=$(hostname)
$ echo $x
example.com
Evaluates to the value of a variable:
$ x=X
$ echo $x ${x}
X X
Shell has C-style arithmetic:
$ echo $(( 1 + 2*3 ))
7
Used as a shortcut for a user's home directory:
~/src # my home dir
~bob/src # user bob's home dir
${a[i+1]}
${x@P} evaluates x as a prompt string, e.g. the string that would be printed if PS1=$x.
Compatible with bash.
Part of dbracket
These backslash escape sequences are used in echo -e, printf,
and in C-style strings like $'foo\n':
\\ backslash
\a alert (BEL)
\b backspace
\c stop processing remaining input
\e the escape character \x1b
\f form feed
\n newline
\r carriage return
\t tab
\v vertical tab
\xHH the byte with value HH, in hexadecimal
\uHHHH the unicode char with value HHHH, in hexadecimal
\UHHHHHHHH the unicode char with value HHHHHHHH, in hexadecimal
Also:
\" Double quote.
Inconsistent octal escapes:
\0NNN echo -e '\0123'
\NNN printf '\123'
echo $'\123'
TODO: Verify other differences between echo -e, printf, and $''. See
frontend/lexer_def.py.
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.
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 numbe 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, onlye 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
source SCRIPT ARG*
Executes SCRIPT with given ARGs in the context of the current shell. It will modify existing variables.
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 is usually unnecessary in Oil code. Using it can confuse code and
user-supplied data, leading to security issues.
Prefer passing single string ARG to eval.
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 builtin modifies the shell's configuration and behavior.
The shopt builtin configures 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.
The complete builtin registers completion policies for different commands.
The compgen builtin generates completion candidates inside a user-defined completion function.
It can also be used in scripts, i.e. outside a completion function.
The compopt builtin changes completion options inside a user-defined completion function.
The compadjust builtin 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.
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.
Oil currently supports writing masks in octal.
If no MODE, show the current mask.
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
Waits for a a process to exit, and returns its status.
The ARG can be a PID (tracked by the kernel), or a job number (tracked by the
shell). Specify jobs with the syntax %jobnumber.
If there's no ARG, wait for all child processes.
Flags:
-n Wait for the next process to exit, rather than a specific process.
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.
Oil 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:
$OPTIND is initialized to 1 every time a shell starts, and is used to
maintain state between invocations of getopts.: and ? can't be flags.TODO
Bash has this, but OSH won't implement it.
help oil # list Oil language help topics
help osh # list OSH language help topics
help TOPIC # show help on a given topic
help osh-usage # same as osh --help
help oil-usage # same as oil --help
View on the web:
https://www.oilshell.org/release/$VERSION/doc/
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. Is it a keyword, shell builtin, shell function, alias, or executable file?
Flags:
-f Don't look for functions
-P Only look for executable files in $PATH
-t Print a single word: alias, builtin, file, function, or keyword
command FLAG* CMD ARG*
Look up CMD as a shell builtin or executable file, and execute it with the given ARGs. That is, the lookup ignores shell functions named CMD.
Flags:
-v Instead of executing CMD, print a description of it.
Similar to the 'type' builtin.
builtin CMD ARG*
Look up CMD as a shell builtin, and execute it with the given ARGs. That is, the lookup ignores shell functions and executables named CMD.
alias NAME=CODE
Make NAME a shortcut for executing CODE, e.g. alias hi='echo hello'.
alias NAME
Show the value of this alias.
alias
Show a list of all aliases.
Tips:
Prefer shell functions like:
ls() {
command ls --color "$@"
}
to aliases like:
alias ls='ls --color'
Functions are less likely to cause parsing problems.
\ls or 'ls' disables alias expansinoTODO: Turn off aliases in Oil.
unalias 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.
Normally, when no files match a glob, the glob itself is returned:
$ echo L *.py R # no Python files in this dir
L *.py R
With nullglob on, the glob expands to no arguments:
shopt -s nullglob
$ echo L *.py R
L R
(This option is in GNU bash as well.)
Do globs return results that start with -? It's on by default in bin/osh,
but off when Oil is enabled.
Turning it off prevents a command like rm * from being confused by a file
called -rf.
$ touch -- myfile -rf
$ echo *
-rf myfile
$ shopt -u dashglob
$ echo *
myfile
For the 'set' builtin.
For the 'shopt' builtin.
$HOME is used for:
Note: The shell doesn't set $HOME. According to POSIX, the program that invokes the login shell sets it based on /etc/passwd.
A colon-separated string that's used to find executables to run.
Used for word splitting. And the builtin split() function.
An array of words, split by : and = for compatibility with bash. New completion scripts should use COMP_ARGV instead.
Discouraged; for compatibility with bash.
Discouraged; for compatibility with bash.
Discouraged; for compatibility with bash.
User-defined completion functions should Fill this array with candidates. It is cleared on every completion request.
An array of partial command arguments to complete. Preferred over COMP_WORDS. The compadjust builtin uses this variable.
(An OSH extension to bash.)
First line of a prompt.
Second line of a prompt.
For the 'select' builtin (unimplemented).
For 'set -o xtrace'. The leading character is special.