| 1 | ---
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| 2 | title: Command Language (Oils Reference)
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| 3 | all_docs_url: ..
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| 4 | body_css_class: width40
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| 5 | default_highlighter: oils-sh
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| 6 | preserve_anchor_case: yes
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| 7 | ---
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| 8 |
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| 9 | <div class="doc-ref-header">
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| 10 |
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| 11 | [Oils Reference](index.html) —
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| 12 | Chapter **Command Language**
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| 13 |
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| 14 | </div>
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| 15 |
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| 16 | This chapter describes the command language for OSH, and some YSH extensions.
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| 17 |
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| 18 | <span class="in-progress">(in progress)</span>
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| 19 |
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| 20 | <div id="dense-toc">
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| 21 | </div>
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| 22 |
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| 23 | ## Quick Sketch: What's a Command?
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| 24 |
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| 25 | OSH:
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| 26 |
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| 27 | print-files() {
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| 28 | for name in *.py; do
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| 29 | if test -x "$name"; then
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| 30 | echo "$name is executable"
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| 31 | fi
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| 32 | done
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| 33 | }
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| 34 |
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| 35 | YSH:
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| 36 |
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| 37 | proc print-files {
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| 38 | for name in *.py {
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| 39 | if test -x $name { # no quotes needed
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| 40 | echo "$name is executable"
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| 41 | }
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| 42 | }
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| 43 | }
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| 44 |
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| 45 |
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| 46 | <h2 id="Commands">Commands</h2>
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| 47 |
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| 48 | <h3 id="simple-command" class="osh-ysh-topic">simple-command</h3>
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| 49 |
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| 50 | Commands are composed of words. The first word may be the name of
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| 51 |
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| 52 | 1. A builtin shell command
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| 53 | 1. A YSH `proc` or shell "function"
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| 54 | 1. A Hay node declared with `hay define`
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| 55 | 1. An external command
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| 56 | 1. An alias
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| 57 |
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| 58 | Examples:
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| 59 |
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| 60 | echo hi # a shell builtin doesn't start a process
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| 61 | ls /usr/bin ~/src # starts a new process
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| 62 | myproc "hello $name"
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| 63 | myshellfunc "hello $name"
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| 64 | myalias -l
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| 65 | <!-- TODO: document lookup order -->
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| 66 |
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| 67 | Redirects are also allowed in any part of the command:
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| 68 |
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| 69 | echo 'to stderr' >&2
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| 70 | echo >&2 'to stderr'
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| 71 |
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| 72 | echo 'to file' > out.txt
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| 73 | echo > out.txt 'to file'
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| 74 |
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| 75 | <h3 id="semicolon" class="osh-ysh-topic">semicolon ;</h3>
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| 76 |
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| 77 | Run two commands in sequence like this:
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| 78 |
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| 79 | echo one; echo two
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| 80 |
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| 81 | or this:
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| 82 |
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| 83 | echo one
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| 84 | echo two
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| 85 |
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| 86 | <h2 id="Conditional">Conditional</h2>
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| 87 |
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| 88 | <h3 id="case" class="osh-topic">case</h3>
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| 89 |
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| 90 | Match a string against a series of glob patterns. Execute code in the section
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| 91 | below the matching pattern.
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| 92 |
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| 93 | path='foo.py'
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| 94 | case "$path" in
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| 95 | *.py)
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| 96 | echo 'python'
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| 97 | ;;
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| 98 | *.sh)
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| 99 | echo 'shell'
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| 100 | ;;
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| 101 | esac
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| 102 |
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| 103 | For bash compatibility, the `;;` terminator can be substituted with either:
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| 104 |
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| 105 | - `;&` - fall through to next arm, ignoring the condition
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| 106 | - `;;&` - fall through to next arm, respecting the condition
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| 107 |
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| 108 | <h3 id="if" class="osh-topic">if</h3>
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| 109 |
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| 110 | Test if a command exited with status zero (true). If so, execute the
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| 111 | corresponding block of code.
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| 112 |
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| 113 | Shell:
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| 114 |
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| 115 | if test -d foo; then
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| 116 | echo 'foo is a directory'
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| 117 | elif test -f foo; then
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| 118 | echo 'foo is a file'
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| 119 | else
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| 120 | echo 'neither'
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| 121 | fi
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| 122 |
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| 123 | YSH:
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| 124 |
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| 125 | if test -d foo {
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| 126 | echo 'foo is a directory'
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| 127 | } elif test -f foo {
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| 128 | echo 'foo is a file'
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| 129 | } else {
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| 130 | echo 'neither'
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| 131 | }
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| 132 |
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| 133 | <h3 id="dbracket" class="osh-topic">dbracket [[</h3>
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| 134 |
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| 135 | Statically parsed boolean expressions, from bash and other shells:
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| 136 |
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| 137 | x=42
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| 138 | if [[ $x -eq 42 ]]; then
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| 139 | echo yes
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| 140 | fi # => yes
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| 141 |
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| 142 | Compare with the [test][] builtin, which is dynamically parsed.
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| 143 |
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| 144 | See [bool-expr][] for the expression syntax.
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| 145 |
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| 146 | [test]: chap-builtin-cmd.html#test
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| 147 | [bool-expr]: chap-mini-lang.html#bool-expr
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| 148 |
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| 149 |
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| 150 | <h3 id="true" class="osh-ysh-topic">true</h3>
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| 151 |
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| 152 | Do nothing and return status 0.
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| 153 |
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| 154 | if true; then
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| 155 | echo hello
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| 156 | fi
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| 157 |
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| 158 | <h3 id="false" class="osh-ysh-topic">false</h3>
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| 159 |
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| 160 | Do nothing and return status 1.
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| 161 |
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| 162 | if false; then
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| 163 | echo 'not reached'
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| 164 | else
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| 165 | echo hello
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| 166 | fi
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| 167 |
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| 168 | <h3 id="colon" class="osh-topic">colon :</h3>
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| 169 |
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| 170 | Like `true`: do nothing and return status 0.
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| 171 |
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| 172 | <h3 id="bang" class="osh-ysh-topic">bang !</h3>
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| 173 |
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| 174 | Invert an exit code:
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| 175 |
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| 176 | if ! test -d /tmp; then
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| 177 | echo "No temp directory
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| 178 | fi
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| 179 |
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| 180 | <h3 id="and" class="osh-ysh-topic">and &&</h3>
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| 181 |
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| 182 | mkdir -p /tmp && cp foo /tmp
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| 183 |
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| 184 | <h3 id="or" class="osh-ysh-topic">or ||</h3>
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| 185 |
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| 186 | ls || die "failed"
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| 187 |
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| 188 | <h2 id="Iteration">Iteration</h2>
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| 189 |
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| 190 | <h3 id="while" class="osh-ysh-topic">while</h3>
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| 191 |
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| 192 | POSIX
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| 193 |
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| 194 | <h3 id="until" class="osh-topic">until</h3>
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| 195 |
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| 196 | POSIX
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| 197 |
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| 198 | <h3 id="for" class="osh-ysh-topic">for</h3>
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| 199 |
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| 200 | For loops iterate over words.
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| 201 |
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| 202 | YSH style:
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| 203 |
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| 204 | var mystr = 'one'
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| 205 | var myarray = :| two three |
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| 206 |
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| 207 | for i in $mystr @myarray *.py {
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| 208 | echo $i
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| 209 | }
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| 210 |
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| 211 |
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| 212 | Shell style:
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| 213 |
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| 214 | local mystr='one'
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| 215 | local myarray=(two three)
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| 216 |
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| 217 | for i in "mystr" "${myarray[@]}" *.py; do
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| 218 | echo $i
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| 219 | done
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| 220 |
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| 221 | Both fragments output 3 lines and then Python files on remaining lines.
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| 222 |
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| 223 | <h3 id="for-expr-sh" class="osh-topic">for-expr-sh</h3>
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| 224 |
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| 225 | A bash/ksh construct:
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| 226 |
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| 227 | for (( i = 0; i < 5; ++i )); do
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| 228 | echo $i
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| 229 | done
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| 230 |
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| 231 | <h2 id="Control Flow">Control Flow</h2>
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| 232 |
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| 233 | These are keywords in Oils, not builtins!
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| 234 |
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| 235 | ### break
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| 236 |
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| 237 | Break out of a loop. (Not used for case statements!)
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| 238 |
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| 239 | ### continue
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| 240 |
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| 241 | Continue to the next iteration of a loop.
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| 242 |
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| 243 | ### return
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| 244 |
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| 245 | Return from a function.
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| 246 |
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| 247 | ### exit
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| 248 |
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| 249 | Exit the shell process with the given status:
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| 250 |
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| 251 | exit 2
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| 252 |
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| 253 | <h2 id="Grouping">Grouping</h2>
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| 254 |
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| 255 | ### sh-func
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| 256 |
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| 257 | POSIX:
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| 258 |
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| 259 | f() {
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| 260 | echo args "$@"
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| 261 | }
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| 262 | f 1 2 3
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| 263 |
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| 264 | ### sh-block
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| 265 |
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| 266 | POSIX:
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| 267 |
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| 268 | { echo one; echo two; }
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| 269 |
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| 270 | The trailing `;` is necessary in OSH, but not YSH. In YSH, `parse_brace` makes
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| 271 | `}` is more of a special word.
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| 272 |
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| 273 |
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| 274 | ### subshell
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| 275 |
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| 276 | ( echo one; echo two )
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| 277 |
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| 278 | In YSH, use [forkwait](chap-builtin-cmd.html#forkwait) instead of parentheses.
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| 279 |
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| 280 | <h2 id="Concurrency">Concurrency</h2>
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| 281 |
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| 282 | ### pipe
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| 283 |
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| 284 | Pipelines are a traditional POSIX shell construct:
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| 285 |
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| 286 | ls /tmp | grep ssh | sort
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| 287 |
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| 288 | Related:
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| 289 |
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| 290 | - [`PIPESTATUS`]() in OSH
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| 291 | - [`_pipeline_status`]() in YSH
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| 292 |
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| 293 | [PIPESTATUS]: chap-special-var.html#PIPESTATUS
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| 294 | [_pipeline_status]: chap-special-var.html#_pipeline_status
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| 295 |
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| 296 | <h3 id="ampersand" class="osh-topic">ampersand &</h3>
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| 297 |
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| 298 | Start a command as a background job. Don't wait for it to finish, and return
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| 299 | control to the shell.
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| 300 |
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| 301 | The PID of the job is recorded in the `$!` variable.
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| 302 |
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| 303 | sleep 1 &
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| 304 | echo pid=$!
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| 305 | { echo two; sleep 2 } &
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| 306 | wait
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| 307 | wait
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| 308 |
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| 309 | In YSH, use the [fork][] builtin.
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| 310 |
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| 311 | [fork]: chap-builtin-cmd.html#fork
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| 312 |
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| 313 |
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| 314 | <h2 id="Redirects">Redirects</h2>
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| 315 |
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| 316 | ### redir-file
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| 317 |
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| 318 | The operators `>` and `>>` redirect the `stdout` of a process to a disk file.
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| 319 | The `<` operator redirects `stdin` from a disk file.
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| 320 |
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| 321 | ---
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| 322 |
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| 323 | Examples of redirecting the `stdout` of a command:
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| 324 |
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| 325 | echo foo > out.txt # overwrite out.txt
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| 326 | date >> stamp.txt # append to stamp.txt
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| 327 |
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| 328 | <!--
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| 329 | echo foo >| out.txt # clobber the file even if set -o noclobber
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| 330 | -->
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| 331 |
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| 332 | Redirect to the `stdin` of a command:
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| 333 |
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| 334 | cat < in.txt
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| 335 |
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| 336 | Redirects are compatible with POSIX and bash, so they take descriptor numbers
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| 337 | on the left:
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| 338 |
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| 339 | make 2> stderr.txt # '2>' is valid, but '2 >' is not
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| 340 |
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| 341 | Note that the word argument to **file** redirects is evaluated like bash, which
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| 342 | is different than other arguments to other redirects:
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| 343 |
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| 344 | tar -x -z < Python* # glob must expand to exactly 1 file
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| 345 | tar -x -z < $myvar # $myvar is split because it's unquoted
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| 346 |
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| 347 | In other words, it's evaluated **as** a sequence of 1 word, which **produces**
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| 348 | zero to N strings. But redirects are only valid when it produces exactly 1
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| 349 | string.
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| 350 |
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| 351 | (Related: YSH uses `shopt --set simple_word_eval`, which means that globs that
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| 352 | match nothing evaluate to zero strings, not themselves.)
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| 353 |
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| 354 | <!-- They also take a file descriptor on the left -->
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| 355 |
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| 356 |
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| 357 | ### redir-desc
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| 358 |
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| 359 | Redirect to a file descriptor:
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| 360 |
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| 361 | echo 'to stderr' >&2
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| 362 |
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| 363 | <!--
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| 364 | NOTE: >&2 is just like <&2
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| 365 | There's no real difference.
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| 366 | -->
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| 367 |
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| 368 | ### here-doc
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| 369 |
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| 370 | Here documents let you write the `stdin` of a process in the shell program.
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| 371 |
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| 372 | Specify a delimiter word (like EOF) after the redir operator (like `<<`).
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| 373 |
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| 374 | If it's unquoted, then `$` expansion happens, like a double-quoted string:
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| 375 |
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| 376 | cat <<EOF
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| 377 | here doc with $double ${quoted} substitution
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| 378 | EOF
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| 379 |
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| 380 | If the delimiter is quoted, then `$` expansion does **not** happen, like a
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| 381 | single-quoted string:
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| 382 |
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| 383 | cat <<'EOF'
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| 384 | price is $3.99
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| 385 | EOF
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| 386 |
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| 387 | Leading tabs can be stripped with the `<<-` operator:
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| 388 |
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| 389 | myfunc() {
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| 390 | cat <<-EOF
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| 391 | here doc with one tab leading tab stripped
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| 392 | EOF
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| 393 | }
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| 394 |
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| 395 | ### here-str
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| 396 |
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| 397 | The `<<<` operator means that the argument is a `stdin` string, not a
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| 398 | chosen delimiter.
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| 399 |
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| 400 | cat <<< 'here string'
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| 401 |
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| 402 | The string **plus a newline** is the `stdin` value, which is consistent with
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| 403 | GNU bash.
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| 404 |
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| 405 | ### ysh-here-str
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| 406 |
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| 407 | You can also use YSH multi-line strings as "here strings". For example:
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| 408 |
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| 409 | Double-quoted:
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| 410 |
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| 411 | cat <<< """
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| 412 | double
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| 413 | quoted = $x
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| 414 | """
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| 415 |
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| 416 | Single-quoted:
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| 417 |
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| 418 | cat <<< '''
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| 419 | price is
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| 420 | $3.99
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| 421 | '''
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| 422 |
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| 423 | J8-style with escapes:
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| 424 |
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| 425 | cat <<< u'''
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| 426 | j8 style string price is
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| 427 | mu = \u{3bc}
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| 428 | '''
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| 429 |
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| 430 | In these cases, a trailing newline is **not** added. For example, the first
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| 431 | example is equivalent to:
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| 432 |
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| 433 | write --end '' -- """
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| 434 | double
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| 435 | quoted = $x
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| 436 | """
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| 437 |
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| 438 | ## Other Command
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| 439 |
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| 440 | <h3 id="dparen" class="osh-topic">dparen ((</h3>
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| 441 |
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| 442 | <h3 id="time" class="osh-ysh-topic">time</h3>
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| 443 |
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| 444 | time [-p] pipeline
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| 445 |
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| 446 | Measures the time taken by a command / pipeline. It uses the `getrusage()`
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| 447 | function from `libc`.
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| 448 |
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| 449 | Note that time is a KEYWORD, not a builtin!
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| 450 |
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| 451 | <!-- Note: bash respects TIMEFORMAT -->
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| 452 |
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| 453 |
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| 454 | ## YSH Simple
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| 455 |
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| 456 | ### typed-arg
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| 457 |
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| 458 | Internal commands (procs and builtins) accept typed arguments in parentheses:
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| 459 |
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| 460 | json write (myobj)
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| 461 |
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| 462 | Redirects can also appear after the typed args:
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| 463 |
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| 464 | json write (myobj) >out.txt
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| 465 |
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| 466 | ### lazy-expr-arg
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| 467 |
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| 468 | Expressions in brackets like this:
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| 469 |
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| 470 | assert [42 === x]
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| 471 |
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| 472 | Are syntactic sugar for:
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| 473 |
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| 474 | assert (^[42 === x])
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| 475 |
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| 476 | That is, it's single arg of type `value.Expr`.
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| 477 |
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| 478 | Redirects can also appear after the lazy typed args:
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| 479 |
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| 480 | assert [42 === x] >out.txt
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| 481 |
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| 482 | ### block-arg
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| 483 |
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| 484 | Blocks can be passed to simple commands, either literally:
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| 485 |
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| 486 | cd /tmp {
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| 487 | echo $PWD # prints /tmp
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| 488 | }
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| 489 | echo $PWD
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| 490 |
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| 491 | Or as an expression:
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| 492 |
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| 493 | var block = ^(echo $PWD)
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| 494 | cd /tmp (; ; block)
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| 495 |
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| 496 | Note that `cd` has no typed or named arguments, so the two semicolons are
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| 497 | preceded by nothing.
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| 498 |
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| 499 | Compare with [sh-block](#sh-block).
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| 500 |
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| 501 | Redirects can appear after the block arg:
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| 502 |
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| 503 | cd /tmp {
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| 504 | echo $PWD # prints /tmp
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| 505 | } >out.txt
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| 506 |
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| 507 | ## YSH Cond
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| 508 |
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| 509 | ### ysh-case
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| 510 |
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| 511 | Like the shell case statement, the Ysh case statement has **string/glob** patterns.
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| 512 |
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| 513 | var s = 'README.md'
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| 514 | case (s) {
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| 515 | *.py { echo 'Python' }
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| 516 | *.cc | *.h { echo 'C++' }
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| 517 | * { echo 'Other' }
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| 518 | }
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| 519 | # => Other
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| 520 |
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| 521 | We also generated it to **typed data** within `()`:
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| 522 |
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| 523 | var x = 43
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| 524 | case (x) {
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| 525 | (30 + 12) { echo 'the integer 42' }
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| 526 | (else) { echo 'neither' }
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| 527 | }
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| 528 | # => neither
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| 529 |
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| 530 | The `else` is a special keyword that matches any value.
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| 531 |
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| 532 | case (s) {
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| 533 | / dot* '.md' / { echo 'Markdown' }
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| 534 | (else) { echo 'neither' }
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| 535 | }
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| 536 | # => Markdown
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| 537 |
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| 538 | ### ysh-if
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| 539 |
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| 540 | Like shell, you can use a command:
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| 541 |
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| 542 | if test --file $x {
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| 543 | echo "$x is a file"
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| 544 | }
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| 545 |
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| 546 | You can also use an expression:
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| 547 |
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| 548 | if (x > 0) {
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| 549 | echo 'positive'
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| 550 | }
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| 551 |
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| 552 | ## YSH Iter
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| 553 |
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| 554 | ### ysh-for
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| 555 |
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| 556 | #### Words
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| 557 |
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| 558 | This is a shell-style loop over "words":
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| 559 |
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| 560 | for name in README.md *.py {
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| 561 | echo $name
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| 562 | }
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| 563 | # => README.md
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| 564 | # => foo.py
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| 565 |
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| 566 | You can also ask for the index:
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| 567 |
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| 568 | for i, name in README.md *.py {
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| 569 | echo "$i $name"
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| 570 | }
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| 571 | # => 0 README.md
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| 572 | # => 1 foo.py
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| 573 |
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| 574 | #### Lines of `stdin`
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| 575 |
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| 576 | Here's how to iterate over the lines of stdin:
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| 577 |
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| 578 | for line in (io.stdin) {
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| 579 | echo $line
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| 580 | }
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| 581 |
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| 582 | Likewise, you can ask for the index with `for i, line in (io.stdin) { ...`.
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| 583 |
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| 584 | ### ysh-while
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| 585 |
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| 586 | You can use an expression as the condition:
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| 587 |
|
| 588 | var x = 5
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| 589 | while (x < 0) {
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| 590 | setvar x -= 1
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| 591 | }
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| 592 |
|
| 593 | You or a command:
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| 594 |
|
| 595 | while test -f myfile {
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| 596 | echo 'myfile'
|
| 597 | sleep 1
|
| 598 | }
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| 599 |
|
| 600 | #### Expressions
|
| 601 |
|
| 602 | Expressions are enclosed in `()`.
|
| 603 |
|
| 604 | Iterating over a `List` or `Range` is like iterating over words or lines:
|
| 605 |
|
| 606 | var mylist = [42, 43]
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| 607 | for item in (mylist) {
|
| 608 | echo $item
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| 609 | }
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| 610 | # => 42
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| 611 | # => 43
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| 612 |
|
| 613 | var n = 5
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| 614 | for i in (3 .. n) {
|
| 615 | echo $i
|
| 616 | }
|
| 617 | # => 3
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| 618 | # => 4
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| 619 |
|
| 620 | However, there are **three** ways of iterating over a `Dict`:
|
| 621 |
|
| 622 | for key in (mydict) {
|
| 623 | echo $key
|
| 624 | }
|
| 625 |
|
| 626 | for key, value in (mydict) {
|
| 627 | echo "$key $value"
|
| 628 | }
|
| 629 |
|
| 630 | for i, key, value in (mydict) {
|
| 631 | echo "$i $key $value"
|
| 632 | }
|
| 633 |
|
| 634 | That is, if you ask for two things, you'll get the key and value. If you ask
|
| 635 | for three, you'll also get the index.
|
| 636 |
|