| 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 | ## Joining
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| 86 |
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| 87 | ### osh-word-join
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| 88 |
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| 89 | OSH joins arbitrary word parts:
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| 90 |
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| 91 | $ myvar=/
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| 92 | $ echo 'single'\'$myvar"double $myvar"
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| 93 | single'/double /
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| 94 |
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| 95 | That is, the argument to `echo` is a word that has 4 word parts:
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| 96 |
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| 97 | 'single'
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| 98 | \'
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| 99 | $myvar
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| 100 | "double $myvar"
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| 101 |
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| 102 | When the word is evaluated, the result of each part is evaluated and
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| 103 | concatenated.
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| 104 |
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| 105 | ### ysh-word-join
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| 106 |
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| 107 | In general, YSH doesn't allow single- and double-quoted parts to be joined.
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| 108 | They most often form an entire word:
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| 109 |
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| 110 | echo 'single-quoted word'
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| 111 | echo "double-quoted word"
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| 112 |
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| 113 | YSH allows word joining in these special cases:
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| 114 |
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| 115 | echo --flag='value'
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| 116 | echo NAME="value"
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| 117 |
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| 118 | echo ~/'dir with spaces'
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| 119 | echo ~root/src/"dir with spaces"
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| 120 |
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| 121 | The purpose of this rule is to eliminate ambiguous words like:
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| 122 |
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| 123 | --flag=u'value\n' # does u indicate a J8 string, or is it a literal?
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| 124 |
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| 125 | See [OILS-ERR-17][] for details.
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| 126 |
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| 127 | [OILS-ERR-17]: ../error-catalog.html#oils-err-17
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| 128 |
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| 129 | ## Quotes
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| 130 |
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| 131 |
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| 132 | ### osh-string
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| 133 |
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| 134 | - Single quotes
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| 135 | - Double Quotes
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| 136 | - C-style strings: `$'\n'`
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| 137 |
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| 138 | TODO: elaborate
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| 139 |
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| 140 | ### ysh-string
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| 141 |
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| 142 | YSH strings in the word language are the same as in the expression language.
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| 143 |
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| 144 | See [ysh-string in chap-expr-lang](chap-expr-lang.html#ysh-string).
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| 145 |
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| 146 | ### triple-quoted
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| 147 |
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| 148 | Triple-quoted in the word language are the same as in the expression language.
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| 149 |
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| 150 | See [triple-quoted in chap-expr-lang](chap-expr-lang.html#triple-quoted).
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| 151 |
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| 152 | ### tagged-str
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| 153 |
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| 154 | Not done.
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| 155 |
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| 156 | ## Substitutions
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| 157 |
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| 158 | ### command-sub
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| 159 |
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| 160 | Executes a command and captures its stdout.
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| 161 |
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| 162 | If stdout has a trailing newline, it's removed:
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| 163 |
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| 164 | $ hostname
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| 165 | example.com
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| 166 |
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| 167 | $ echo "/tmp/$(hostname)"
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| 168 | /tmp/example.com
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| 169 |
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| 170 | If stdout has any NUL bytes, they are removed (regardless of position).
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| 171 |
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| 172 | Related: [captureStdout()](chap-type-method.html#captureStdout)
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| 173 |
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| 174 | ### ysh-command-sub
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| 175 |
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| 176 | YSH also has spliced command subs, enabled by `shopt --set parse_at`. The
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| 177 | result is a **List** of strings, rather than a single string.
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| 178 |
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| 179 | $ write -- @(echo foo; echo 'with spaces')
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| 180 | foo
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| 181 | with-spaces
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| 182 |
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| 183 | The command's stdout parsed as the "J8 Lines" format, where each line is
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| 184 | either:
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| 185 |
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| 186 | 1. An unquoted string, which must be valid UTF-8. Whitespace is allowed, but
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| 187 | not other ASCII control chars.
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| 188 | 2. A quoted J8 string (JSON style `""` or J8-style `b'' u'' ''`)
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| 189 | 3. An **ignored** empty line
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| 190 |
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| 191 | See [J8 Notation](../j8-notation.html) for more details.
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| 192 |
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| 193 | ### var-sub
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| 194 |
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| 195 | Evaluates to the value of a variable:
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| 196 |
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| 197 | $ x=X
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| 198 | $ echo $x ${x}
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| 199 | X X
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| 200 |
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| 201 | ### arith-sub
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| 202 |
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| 203 | Shell has C-style arithmetic:
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| 204 |
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| 205 | $ echo $(( 1 + 2*3 ))
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| 206 | 7
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| 207 |
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| 208 | ### tilde-sub
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| 209 |
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| 210 | Used as a shortcut for a user's home directory:
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| 211 |
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| 212 | ~/src # my home dir
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| 213 | ~bob/src # user bob's home dir
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| 214 |
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| 215 | ### proc-sub
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| 216 |
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| 217 | Open stdout as a named file in `/dev/fd`, which can be passed to a command:
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| 218 |
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| 219 | diff <(sort L.txt) <(sort R.txt)
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| 220 |
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| 221 | Open stdin as a named file in `/dev/fd`:
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| 222 |
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| 223 | seq 3 | tee >(sleep 1; tac)
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| 224 |
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| 225 |
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| 226 | ## Var Ops
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| 227 |
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| 228 | There are three types of braced variable expansions:
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| 229 |
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| 230 | ${!name*} or ${!name@}
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| 231 | ${!name[@]} or ${!name[*]}
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| 232 | ${ops var ops}
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| 233 |
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| 234 | `name` needs to be a valid identifier. If the expansion matches the first
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| 235 | form, the variable names starting with `name` are generated. Otherwise, if the
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| 236 | expansion matches the second form, the keys of the indexed or associative array
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| 237 | named `name` are generated. When the expansion does not much either the first
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| 238 | or second forms, it is interpreted as the third form of the variable name
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| 239 | surrounded by operators.
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| 240 |
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| 241 |
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| 242 | ### op-bracket
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| 243 |
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| 244 | The value within brackets is called an "index", and retrieves a value from an
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| 245 | array:
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| 246 |
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| 247 | ${A[i+1]}
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| 248 | ${A['key']}
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| 249 |
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| 250 | If `A` is an indexed array, the index is interpreted as an arithmetic
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| 251 | expression. Arithmetic evaluation is performed, and the value at that numeric
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| 252 | offset is retrieved.
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| 253 |
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| 254 | If `A` is an associative array, the index is interpreted as a string. The
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| 255 | value associated with that string is retrieved.
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| 256 |
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| 257 | If `A` is a string, it's treated as an indexed array with a single element,
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| 258 | i.e. so that `${A[0]}` is `${A}`.
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| 259 |
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| 260 | ---
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| 261 |
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| 262 | ${A[*]}
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| 263 | ${A[@]}
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| 264 |
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| 265 | The index expressions `[*]` and `[@]` are special cases. Both generate a word
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| 266 | list of all elements in `a`.
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| 267 |
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| 268 | When the variable substitution is **unquoted**, there's no difference between
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| 269 | `[*]` and `[@]`:
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| 270 |
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| 271 | $ A=(1 2 3)
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| 272 | $ printf '<%s>\n' ${A[*]}
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| 273 | <1>
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| 274 | <2>
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| 275 | <3>
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| 276 |
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| 277 | $ printf '<%s>\n' ${A[@]}
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| 278 | <1>
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| 279 | <2>
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| 280 | <3>
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| 281 |
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| 282 | When double-quoted, the `[*]` form joins the elements by the first character of
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| 283 | `IFS`:
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| 284 |
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| 285 | $ IFS=x
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| 286 | $ printf '<%s>\n' "${A[*]}"
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| 287 | <1x2x3>
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| 288 |
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| 289 | When double-quoted, the `[@]` form generates a word list by splitting the word
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| 290 | at the boundary of every element in `A`:
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| 291 |
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| 292 | $ printf '<%s>\n' "-${A[@]}-"
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| 293 | <-1>
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| 294 | <2>
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| 295 | <3->
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| 296 |
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| 297 | If the container `A` has no elements, and the variable substitution has no
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| 298 | other parts, `[@]` evaluates to an empty word list:
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| 299 |
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| 300 | $ empty=()
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| 301 | $ set -- "${empty[@]}"
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| 302 | $ echo $#
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| 303 | 0
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| 304 |
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| 305 | ---
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| 306 |
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| 307 | These rules for `[*]` and `[@]` also apply to:
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| 308 |
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| 309 | - `$*` and `$@`
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| 310 | - `${!name*}` and `${!name@}`
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| 311 | - `${!name[*]}` and `${!name[@]}`, etc.
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| 312 |
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| 313 | <!--
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| 314 | Note: OSH currently joins the values by `IFS` even for unquoted `$*` and
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| 315 | performs word splitting afterward. This is different from the POSIX standard.
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| 316 | -->
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| 317 |
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| 318 | ### op-indirect
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| 319 |
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| 320 | The indirection operator `!` is a prefix operator, and it interprets the
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| 321 | received string as a variable name `name`, an array element `name[key]`, or an
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| 322 | arrat list `name[@]` / `name[*]` and reads its values.
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| 323 |
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| 324 | $ a=1234
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| 325 | $ v=a
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| 326 | $ echo $v
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| 327 | a
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| 328 | $ echo ${!v}
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| 329 | 1234
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| 330 |
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| 331 | ### op-test
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| 332 |
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| 333 | Shell has boolean operations within `${}`. I use `:-` most frequently:
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| 334 |
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| 335 | x=${1:-default}
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| 336 | osh=${OSH:-default}
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| 337 |
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| 338 | This idiom is also useful:
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| 339 |
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| 340 | : ${LIB_OSH=stdlib/osh}
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| 341 |
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| 342 | ---
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| 343 |
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| 344 | There are test operators with colons, and without:
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| 345 |
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| 346 | ${x-default}
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| 347 | ${x:-default}
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| 348 |
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| 349 | ${x=default}
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| 350 | ${x:=default}
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| 351 |
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| 352 | ${x+other}
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| 353 | ${x:+other}
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| 354 |
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| 355 | ${x?error}
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| 356 | ${x:?error}
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| 357 |
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| 358 | **Without** the colon, the shell checks whether a value is **defined**. In the
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| 359 | case of a word list, e.g. generated by `$*` or `$@`, it tests whether there is
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| 360 | at least one element.
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| 361 |
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| 362 | **With** the colon, the shell checks whether the value is **non-empty** (is not
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| 363 | the empty string). In the case of a word list, the test is performed after
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| 364 | joining the elements by a space.
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| 365 |
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| 366 | Elements are joined by the first character of `IFS` only with double-quoted
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| 367 | `"${*:-}"`.
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| 368 |
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| 369 | In contrast, `${*:-}`, `${@:-}`, and `"${@:-}"` are joined by a space. This is
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| 370 | because the joining of `"$*"` by `IFS` is performed earlier than the joining by
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| 371 | space for the test.
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| 372 |
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| 373 | <!--
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| 374 | Note: OSH currently joins the values by `IFS` even for unquoted `$*`. This is
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| 375 | different from Bash.
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| 376 | -->
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| 377 |
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| 378 | ### op-strip
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| 379 |
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| 380 | Remove prefixes or suffixes from strings:
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| 381 |
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| 382 | echo ${y#prefix}
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| 383 | echo ${y##'prefix'}
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| 384 |
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| 385 | echo ${y%suffix}
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| 386 | echo ${y%%'suffix'}
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| 387 |
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| 388 | The prefix and suffix can be glob patterns, but this usage is discouraged
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| 389 | because it may be slow.
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| 390 |
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| 391 | ### op-patsub
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| 392 |
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| 393 | Replace a substring or pattern.
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| 394 |
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| 395 | The character after the first `/` can be `/` to replace all occurrences:
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| 396 |
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| 397 | $ x=food
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| 398 |
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| 399 | $ echo ${x//o/--} # replace 1 o with 2 --
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| 400 | f----d
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| 401 |
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| 402 | It can be `#` or `%` for an anchored replacement:
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| 403 |
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| 404 | $ echo ${x/#f/--} # left anchored f
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| 405 | --ood
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| 406 |
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| 407 | $ echo ${x/%d/--} # right anchored d
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| 408 | foo--
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| 409 |
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| 410 | The pattern can also be a glob:
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| 411 |
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| 412 | $ echo ${x//[a-z]/o} # replace 1 char with o
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| 413 | oooo
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| 414 |
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| 415 | $ echo ${x//[a-z]+/o} # replace multiple chars
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| 416 | o
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| 417 |
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| 418 | ### op-slice
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| 419 |
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| 420 | echo ${a[@]:1:2}
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| 421 | echo ${@:1:2}
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| 422 |
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| 423 | ### op-format
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| 424 |
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| 425 | ${x@P} evaluates x as a prompt string, i.e. the string that would be printed if
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| 426 | PS1=$x.
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| 427 |
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| 428 | ---
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| 429 |
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| 430 | `${x@Q}` quotes the value of `x`, if necessary, so that it can be evaluated as
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| 431 | a shell word.
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| 432 |
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| 433 | $ x='<'
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| 434 | $ echo "value = $x, quoted = ${x@Q}."
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| 435 | value = <, quoted = '<'.
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| 436 |
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| 437 | $ x=a
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| 438 | $ echo "value = $x, quoted = ${x@Q}."
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| 439 | value = a, quoted = a.
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| 440 |
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| 441 | In the second case, the string `a` doesn't need to be quoted.
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| 442 |
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| 443 | ---
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| 444 |
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| 445 | Format operations like `@Q` generally treat **empty** variables differently
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| 446 | than **unset** variables.
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| 447 |
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| 448 | That is, `${empty@Q}` is the string `''`, while `${unset@Q}` is an empty
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| 449 | string:
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| 450 |
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| 451 | $ x=''
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| 452 | $ echo "value = $x, quoted = ${x@Q}."
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| 453 | value = , quoted = ''.
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| 454 |
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| 455 | $ unset -v x
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| 456 | $ echo "value = $x, quoted = ${x@Q}."
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| 457 | value = , quoted = .
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| 458 |
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| 459 | ---
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| 460 |
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| 461 | `${x@a}` returns characters that represent the attributes of the `${x}`, or
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| 462 | more precisely, the *h-value* of `${x}`.
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| 463 |
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| 464 | Definitions:
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| 465 |
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| 466 | - *h-value* is the variable (or the object that the variable directly points)
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| 467 | from which the result of `${x}` would originally come.
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| 468 | - *r-value* is the value of the expansion of `${x}`
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| 469 |
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| 470 | For example, with `arr=(1 2 3)`:
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| 471 |
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| 472 | <style>
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| 473 | table {
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| 474 | width: 100%;
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| 475 | margin-left: 2em; /* matches p text in manual.css */
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| 476 | }
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| 477 | thead {
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| 478 | text-align: left;
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| 479 | }
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| 480 | </style>
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| 481 |
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| 482 | <table>
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| 483 |
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| 484 | - thead
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| 485 | - Reference
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| 486 | - Expression
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| 487 | - H-value
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| 488 | - R-value
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| 489 | - Flags returned
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| 490 | - tr
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| 491 | - <!-- empty -->
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| 492 | - `${arr[0]@a}` or <br/> `${arr@a}`
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| 493 | - array<br/> `(1 2 3)`
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| 494 | - string<br/> `1`
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| 495 | - `a`
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| 496 | - tr
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| 497 | - <!-- empty -->
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| 498 | - `${arr[@]@a}`
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| 499 | - array<br/> `(1 2 3)`
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| 500 | - array<br/> `(1 2 3)`
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| 501 | - `a a a`
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| 502 | - tr
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| 503 | - `ref=arr` or `ref=arr[0]`
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| 504 | - `${!ref@a}`
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| 505 | - array<br/> `(1 2 3)`
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| 506 | - string<br/> `1`
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| 507 | - `a`
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| 508 | - <!-- empty -->
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| 509 | - tr
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| 510 | - `ref=arr[@]`
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| 511 | - `${!ref@a}`
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| 512 | - array<br/> `(1 2 3)`
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| 513 | - array<br/> `(1 2 3)`
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| 514 | - `a a a`
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| 515 |
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| 516 | </table>
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| 517 |
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| 518 | When `${x}` would result in a word list, `${x@a}` returns a word list
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| 519 | containing the attributes of the *h-value* of each word.
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| 520 |
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| 521 | ---
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| 522 |
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| 523 | These characters may be returned:
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| 524 |
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| 525 | <table>
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| 526 |
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| 527 | - thead
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| 528 | - Character
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| 529 | - Where `${x}` would be obtained
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| 530 | - tr
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| 531 | - `a`
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| 532 | - indexed array
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| 533 | - tr
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| 534 | - `A`
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| 535 | - associative array
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| 536 | - tr
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| 537 | - `r`
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| 538 | - readonly container
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| 539 | - tr
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| 540 | - `x`
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| 541 | - exported variable
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| 542 | - tr
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| 543 | - `n`
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| 544 | - name reference (OSH extension)
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| 545 |
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| 546 | </table>
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