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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