| 1 | ---
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| 2 | title: Word 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 **Word 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 word language for OSH and YSH. Words evaluate to
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| 17 | strings, or arrays of strings.
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| 18 |
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| 19 | <span class="in-progress">(in progress)</span>
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| 20 |
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| 21 | <div id="dense-toc">
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| 22 | </div>
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| 23 |
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| 24 | <h2 id="expression">Expressions to Words</h2>
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| 25 |
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| 26 | ### expr-sub
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| 27 |
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| 28 | Try to turn an expression into a string. Examples:
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| 29 |
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| 30 | $ echo $[3 * 2]
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| 31 | 6
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| 32 |
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| 33 | $ var s = 'foo'
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| 34 | $ echo $[s[1:]]
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| 35 | oo
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| 36 |
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| 37 | Some types can't be stringified, like Dict and List:
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| 38 |
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| 39 | $ var d = {k: 42}
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| 40 |
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| 41 | $ echo $[d]
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| 42 | fatal: expected Null, Bool, Int, Float, Eggex
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| 43 |
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| 44 | You can explicitly use `toJson8` or `toJson()`:
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| 45 |
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| 46 | $ echo $[toJson8(d)]
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| 47 | {"k":42}
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| 48 |
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| 49 | (This is similar to `json write (d)`)
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| 50 |
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| 51 | ### expr-splice
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| 52 |
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| 53 | Splicing puts the elements of a `List` into a string array context:
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| 54 |
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| 55 | $ var foods = ['ale', 'bean', 'corn']
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| 56 | $ echo pizza @[foods[1:]] worm
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| 57 | pizza bean corn worm
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| 58 |
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| 59 | This syntax is enabled by `shopt --set` [parse_at][], which is part of YSH.
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| 60 |
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| 61 | [parse_at]: chap-option.html#ysh:upgrade
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| 62 |
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| 63 | ### var-splice
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| 64 |
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| 65 | $ var foods = ['ale', 'bean', 'corn']
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| 66 | echo @foods
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| 67 |
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| 68 | This syntax is enabled by `shopt --set` [parse_at][], which is part of YSH.
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| 69 |
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| 70 |
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| 71 | <h2 id="formatting">Formatting Typed Data as Strings</h2>
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| 72 |
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| 73 | ### ysh-printf
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| 74 |
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| 75 | Not done.
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| 76 |
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| 77 | echo ${x %.3f}
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| 78 |
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| 79 | ### ysh-format
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| 80 |
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| 81 | Not done.
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| 82 |
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| 83 | echo ${x|html}
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| 84 |
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| 85 | ## Quotes
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| 86 |
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| 87 | ### osh-string
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| 88 |
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| 89 | - Single quotes
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| 90 | - Double Quotes
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| 91 | - C-style strings: `$'\n'`
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| 92 |
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| 93 | TODO: elaborate
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| 94 |
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| 95 | ### ysh-string
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| 96 |
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| 97 | YSH strings in the word language are the same as in the expression language.
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| 98 |
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| 99 | See [ysh-string in chap-expr-lang](chap-expr-lang.html#ysh-string).
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| 100 |
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| 101 | ### triple-quoted
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| 102 |
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| 103 | Triple-quoted in the word language are the same as in the expression language.
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| 104 |
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| 105 | See [triple-quoted in chap-expr-lang](chap-expr-lang.html#triple-quoted).
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| 106 |
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| 107 | ### tagged-str
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| 108 |
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| 109 | Not done.
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| 110 |
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| 111 | ## Substitutions
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| 112 |
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| 113 | ### command-sub
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| 114 |
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| 115 | Executes a command and captures its stdout.
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| 116 |
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| 117 | OSH has shell-compatible command sub like `$(echo hi)`. If a trailing newline
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| 118 | is returned, it's removed:
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| 119 |
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| 120 | $ hostname
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| 121 | example.com
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| 122 |
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| 123 | $ echo "/tmp/$(hostname)"
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| 124 | /tmp/example.com
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| 125 |
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| 126 | YSH has spliced command subs, enabled by `shopt --set parse_at`. The result is
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| 127 | a **List** of strings, rather than a single string.
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| 128 |
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| 129 | $ write -- @(echo foo; echo 'with spaces')
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| 130 | foo
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| 131 | with-spaces
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| 132 |
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| 133 | The command's stdout parsed as the "J8 Lines" format, where each line is
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| 134 | either:
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| 135 |
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| 136 | 1. An unquoted string, which must be valid UTF-8. Whitespace is allowed, but
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| 137 | not other ASCII control chars.
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| 138 | 2. A quoted J8 string (JSON style `""` or J8-style `b'' u'' ''`)
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| 139 | 3. An **ignored** empty line
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| 140 |
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| 141 | See [J8 Notation](../j8-notation.html) for more details.
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| 142 |
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| 143 | ### var-sub
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| 144 |
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| 145 | Evaluates to the value of a variable:
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| 146 |
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| 147 | $ x=X
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| 148 | $ echo $x ${x}
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| 149 | X X
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| 150 |
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| 151 | ### arith-sub
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| 152 |
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| 153 | Shell has C-style arithmetic:
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| 154 |
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| 155 | $ echo $(( 1 + 2*3 ))
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| 156 | 7
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| 157 |
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| 158 | ### tilde-sub
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| 159 |
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| 160 | Used as a shortcut for a user's home directory:
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| 161 |
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| 162 | ~/src # my home dir
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| 163 | ~bob/src # user bob's home dir
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| 164 |
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| 165 | ### proc-sub
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| 166 |
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| 167 | Open stdout as a named file in `/dev/fd`, which can be passed to a command:
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| 168 |
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| 169 | diff <(sort L.txt) <(sort R.txt)
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| 170 |
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| 171 | Open stdin as a named file in `/dev/fd`:
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| 172 |
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| 173 | seq 3 | tee >(sleep 1; tac)
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| 174 |
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| 175 |
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| 176 | ## Var Ops
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| 177 |
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| 178 | There are three types of braced variable expansions:
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| 179 |
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| 180 | ${!name*} or ${!name@}
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| 181 | ${!name[@]} or ${!name[*]}
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| 182 | ${ops var ops}
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| 183 |
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| 184 | `name` needs to be a valid identifier. If the expansion matches the first
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| 185 | form, the variable names starting with `name` are generated. Otherwise, if the
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| 186 | expansion matches the second form, the keys of the indexed or associative array
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| 187 | named `name` are generated. When the expansion does not much either the first
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| 188 | or second forms, it is interpreted as the third form of the variable name
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| 189 | surrounded by operators.
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| 190 |
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| 191 |
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| 192 | ### op-indirect
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| 193 |
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| 194 | The indirection operator `!` is a prefix operator, and it interprets the
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| 195 | received string as a variable name `name`, an array element `name[key]`, or an
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| 196 | arrat list `name[@]` / `name[*]` and reads its values.
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| 197 |
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| 198 | $ a=1234
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| 199 | $ v=a
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| 200 | $ echo $v
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| 201 | a
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| 202 | $ echo ${!v}
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| 203 | 1234
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| 204 |
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| 205 | ### op-test
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| 206 |
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| 207 | Shell has boolean operations within `${}`. I use `:-` most frequently:
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| 208 |
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| 209 | x=${1:-default}
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| 210 | osh=${OSH:-default}
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| 211 |
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| 212 | This idiom is also useful:
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| 213 |
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| 214 | : ${LIB_OSH=stdlib/osh}
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| 215 |
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| 216 | ### op-strip
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| 217 |
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| 218 | Remove prefixes or suffixes from strings:
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| 219 |
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| 220 | echo ${y#prefix}
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| 221 | echo ${y##'prefix'}
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| 222 |
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| 223 | echo ${y%suffix}
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| 224 | echo ${y%%'suffix'}
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| 225 |
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| 226 | The prefix and suffix can be glob patterns, but this usage is discouraged
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| 227 | because it may be slow.
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| 228 |
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| 229 | ### op-patsub
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| 230 |
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| 231 | Replace a substring or pattern.
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| 232 |
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| 233 | The character after the first `/` can be `/` to replace all occurrences:
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| 234 |
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| 235 | $ x=food
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| 236 |
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| 237 | $ echo ${x//o/--} # replace 1 o with 2 --
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| 238 | f----d
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| 239 |
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| 240 | It can be `#` or `%` for an anchored replacement:
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| 241 |
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| 242 | $ echo ${x/#f/--} # left anchored f
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| 243 | --ood
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| 244 |
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| 245 | $ echo ${x/%d/--} # right anchored d
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| 246 | foo--
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| 247 |
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| 248 | The pattern can also be a glob:
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| 249 |
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| 250 | $ echo ${x//[a-z]/o} # replace 1 char with o
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| 251 | oooo
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| 252 |
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| 253 | $ echo ${x//[a-z]+/o} # replace multiple chars
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| 254 | o
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| 255 |
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| 256 | ### op-index
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| 257 |
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| 258 | echo ${a[i+1]}
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| 259 |
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| 260 | ### op-slice
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| 261 |
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| 262 | echo ${a[@]:1:2}
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| 263 | echo ${@:1:2}
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| 264 |
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| 265 | ### op-format
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| 266 |
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| 267 | ${x@P} evaluates x as a prompt string, i.e. the string that would be printed if
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| 268 | PS1=$x.
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| 269 |
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| 270 | ---
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| 271 |
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| 272 | `${x@Q}` quotes the value of `x`, if necessary, so that it can be evaluated as
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| 273 | a shell word.
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| 274 |
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| 275 | $ x='<'
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| 276 | $ echo "value = $x, quoted = ${x@Q}."
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| 277 | value = <, quoted = '<'.
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| 278 |
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| 279 | $ x=a
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| 280 | $ echo "value = $x, quoted = ${x@Q}."
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| 281 | value = a, quoted = a.
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| 282 |
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| 283 | In the second case, the string `a` doesn't need to be quoted.
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| 284 |
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| 285 | ---
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| 286 |
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| 287 | Format operations like `@Q` generally treat **empty** variables differently
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| 288 | than **unset** variables.
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| 289 |
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| 290 | That is, `${empty@Q}` is the string `''`, while `${unset@Q}` is an empty
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| 291 | string:
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| 292 |
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| 293 | $ x=''
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| 294 | $ echo "value = $x, quoted = ${x@Q}."
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| 295 | value = , quoted = ''.
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| 296 |
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| 297 | $ unset -v x
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| 298 | $ echo "value = $x, quoted = ${x@Q}."
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| 299 | value = , quoted = .
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