| 1 | ---
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| 2 | title: Mini Languages (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 **Mini Languages**
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| 13 |
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| 14 | </div>
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| 15 |
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| 16 | This chapter describes "mini-languages" like glob patterns and brace expansion.
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| 17 |
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| 18 | In contrast, the main sub languages of YSH are [command](chap-cmd-lang.html),
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| 19 | [word](chap-word-lang.html), and [expression](chap-expr-lang.html).
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| 20 |
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| 21 | <span class="in-progress">(in progress)</span>
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| 22 |
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| 23 | <div id="dense-toc">
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| 24 | </div>
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| 25 |
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| 26 | <h2 id="sublang">Other Shell Sublanguages</h2>
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| 27 |
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| 28 | ## Arithmetic
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| 29 |
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| 30 | ### arith-context
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| 31 |
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| 32 | Arithmetic expressions are parsed and evaluated in many parts of POSIX shell
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| 33 | and bash.
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| 34 |
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| 35 | Static:
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| 36 |
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| 37 | a=$(( x + 1 )) # POSIX shell
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| 38 |
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| 39 | # bash
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| 40 | (( a = x + 1 ))
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| 41 |
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| 42 | for (( i = 0; i < n; ++i )); do
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| 43 | echo $i
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| 44 | done
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| 45 |
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| 46 | Dynamic:
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| 47 |
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| 48 | [[ 5 -eq 3+x ]] # but not test 5 -eq 3+x
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| 49 |
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| 50 | Array index contexts:
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| 51 |
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| 52 | echo ${a[i+1]} # get
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| 53 | echo ${#a[i+1]} # calculate
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| 54 |
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| 55 | a[i+1]=foo # set
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| 56 |
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| 57 | printf -v 'a[i+1]' # assign to this location
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| 58 | unset 'a[i+1]' # unset location
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| 59 |
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| 60 | echo ${a[@] : i+1 : i+2 } # bash slicing
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| 61 |
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| 62 | bash allows similar array expressions with `test -v`:
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| 63 |
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| 64 | test -v 'array[i+1]' # is array item set?
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| 65 | test -v 'assoc[$myvar]' # is assoc array key set?
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| 66 |
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| 67 | [[ -v 'array[i+1]' ]] # ditto
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| 68 | [[ -v 'assoc[$myvar]' ]]
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| 69 |
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| 70 | But OSH allows only integers and "bare" string constants:
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| 71 |
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| 72 | test -v 'array[42]' # is array item set?
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| 73 | test -v 'assoc[key]' # is assoc array key set?
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| 74 |
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| 75 | ### sh-numbers
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| 76 |
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| 77 | ### sh-arith
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| 78 |
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| 79 | ### sh-logical
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| 80 |
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| 81 | ### sh-bitwise
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| 82 |
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| 83 | ## Boolean
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| 84 |
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| 85 | ### bool-expr
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| 86 |
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| 87 | Boolean expressions can be use the `test` builtin:
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| 88 |
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| 89 | test ! $x -a $y -o $z
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| 90 |
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| 91 | Or the `[[` command language:
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| 92 |
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| 93 | [[ ! $x && $y || $z ]]
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| 94 |
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| 95 | ### bool-infix
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| 96 |
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| 97 | Examples:
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| 98 |
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| 99 | test $a -nt $b
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| 100 | test $x == $y
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| 101 |
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| 102 | ### bool-path
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| 103 |
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| 104 | Example:
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| 105 |
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| 106 | test -d /etc
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| 107 | test -e /
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| 108 | test -f myfile
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| 109 |
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| 110 | YSH has long flags:
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| 111 |
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| 112 | test --dir /etc
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| 113 | test --exists /
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| 114 | test --file myfile
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| 115 |
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| 116 | ### bool-str
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| 117 |
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| 118 | test -n foo # => status 0 / true -- foo is non-empty
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| 119 | test -z '' # => status 0 / true -- '' is empty / zero-length
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| 120 |
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| 121 | ### bool-other
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| 122 |
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| 123 | Test if a shell option is set:
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| 124 |
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| 125 | test -o errexit
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| 126 |
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| 127 | Test the values of variables:
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| 128 |
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| 129 | test -v var_name # is variable defined?
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| 130 | test -v name[index] # is an entry in a container set?
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| 131 |
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| 132 | Notes:
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| 133 |
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| 134 | - In `name[index]`, OSH doesn't allow arithmetic expressions / dynamic parsing,
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| 135 | as bash does.
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| 136 | - `shopt --set strict_word_eval` exposes "syntax errors" in `name[index]`, and
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| 137 | is recommended.
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| 138 | - Without this option, `test -v` will silently return `1` (false) when given
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| 139 | nonsense input, like `test -v /`.
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| 140 |
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| 141 | ## Patterns
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| 142 |
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| 143 | ### glob-pat
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| 144 |
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| 145 | TODO: glob syntax
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| 146 |
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| 147 | ### extglob
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| 148 |
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| 149 | TODO: extended glob syntax
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| 150 |
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| 151 | ### regex
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| 152 |
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| 153 | Part of [dbracket](chap-cmd-lang.html#dbracket)
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| 154 |
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| 155 | ## Other Sublang
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| 156 |
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| 157 | ### braces
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| 158 |
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| 159 | ### histsub
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| 160 |
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| 161 | History substitution uses `!`.
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| 162 |
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| 163 | ### char-escapes
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| 164 |
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| 165 | These backslash escape sequences are used in [echo
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| 166 | -e](chap-builtin-cmd.html#echo), [printf](chap-builtin-cmd.html#printf), and in
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| 167 | C-style strings like `$'foo\n'`:
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| 168 |
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| 169 | \\ backslash
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| 170 | \a alert (BEL)
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| 171 | \b backspace
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| 172 | \c stop processing remaining input
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| 173 | \e the escape character \x1b
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| 174 | \f form feed
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| 175 | \n newline
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| 176 | \r carriage return
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| 177 | \t tab
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| 178 | \v vertical tab
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| 179 | \xHH the byte with value HH, in hexadecimal
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| 180 | \uHHHH the unicode char with value HHHH, in hexadecimal
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| 181 | \UHHHHHHHH the unicode char with value HHHHHHHH, in hexadecimal
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| 182 |
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| 183 | Also:
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| 184 |
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| 185 | \" Double quote.
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| 186 |
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| 187 | Inconsistent octal escapes:
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| 188 |
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| 189 | \0NNN echo -e '\0123'
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| 190 | \NNN printf '\123'
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| 191 | echo $'\123'
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| 192 |
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| 193 | TODO: Verify other differences between `echo -e`, `printf`, and `$''`. See
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| 194 | `frontend/lexer_def.py`.
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| 195 |
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