| 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 | Glob patterns look like:
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| 146 |
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| 147 | echo *.py # Ends with .py
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| 148 | echo *.[ch] # Ends with .c or .h
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| 149 |
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| 150 | This syntax is used in:
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| 151 |
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| 152 | - "Array of words" contexts ([osh-glob][], [ysh-glob][])
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| 153 | - [simple-command][] - like `echo *.py`
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| 154 | - bash arrays `a=( *.py )`
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| 155 | - YSH arrays `var a = :| *.py |`
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| 156 | - for loops `for x in *.py; do ...`
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| 157 | - [case][] patterns
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| 158 | - [dbracket][] matching - `[[ x == *.py ]]`
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| 159 | - Word operations
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| 160 | - [op-strip][] - `${x#*.py}`
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| 161 | - [op-patsub][] - `${x//*.py/replace}` -
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| 162 |
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| 163 | [osh-glob]: chap-word-lang.html#osh-glob
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| 164 | [ysh-glob]: chap-word-lang.html#ysh-glob
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| 165 |
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| 166 | [simple-command]: chap-cmd-lang.html#simple-command
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| 167 | [case]: chap-cmd-lang.html#case
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| 168 | [dbracket]: chap-cmd-lang.html#dbracket
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| 169 |
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| 170 | [op-strip]: chap-word-lang.html#op-strip
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| 171 | [op-patsub]: chap-word-lang.html#op-patsub
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| 172 |
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| 173 | ### extglob
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| 174 |
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| 175 | Extended globs let you use logical operations with globs.
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| 176 |
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| 177 | They may be **slow**. Regexes and eggexes are preferred.
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| 178 |
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| 179 | echo @(*.cc|*.h) # Show files ending with .cc or .h
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| 180 | echo !(*.cc|*.h) # Show every file that does NOT end with .cc or .h
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| 181 |
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| 182 | Extended globs can appear in most of the places globs can, except
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| 183 | [op-patsub][] (because we implement it by translating.
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| 184 |
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| 185 | ### regex
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| 186 |
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| 187 | POSIX ERE (extended regular expressions) are part of bash's [dbracket][]:
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| 188 |
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| 189 | x=123
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| 190 | if [[ x =~ '[0-9]+ ]]; then
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| 191 | echo 'looks like a number'
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| 192 | fi
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| 193 |
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| 194 | ## Other Sublang
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| 195 |
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| 196 | ### braces
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| 197 |
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| 198 | Brace expansion saves you typing:
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| 199 |
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| 200 | $ echo {foo,bar}@example.com
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| 201 | foo@example.com bar@example.com
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| 202 |
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| 203 | You can use it with number ranges:
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| 204 |
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| 205 | $ echo foo{1..3}
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| 206 | foo1 foo2 foo3
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| 207 |
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| 208 | (The numbers must be **constant**.)
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| 209 |
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| 210 | Technically, it does a cartesian product, which is 3 X 2 in this case:
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| 211 |
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| 212 | $ for x in foo{1..3}-{X,Y}; do echo $x; done
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| 213 | foo1-X
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| 214 | foo1-Y
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| 215 | foo2-X
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| 216 | foo2-Y
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| 217 | foo3-X
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| 218 | foo3-Y
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| 219 |
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| 220 | ### histsub
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| 221 |
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| 222 | History substitution uses `!`.
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| 223 |
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| 224 | ### char-escapes
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| 225 |
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| 226 | These backslash escape sequences are used in [echo
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| 227 | -e](chap-builtin-cmd.html#echo), [printf](chap-builtin-cmd.html#printf), and in
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| 228 | C-style strings like `$'foo\n'`:
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| 229 |
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| 230 | \\ backslash
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| 231 | \a alert (BEL)
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| 232 | \b backspace
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| 233 | \c stop processing remaining input
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| 234 | \e the escape character \x1b
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| 235 | \f form feed
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| 236 | \n newline
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| 237 | \r carriage return
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| 238 | \t tab
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| 239 | \v vertical tab
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| 240 | \xHH the byte with value HH, in hexadecimal
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| 241 | \uHHHH the unicode char with value HHHH, in hexadecimal
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| 242 | \UHHHHHHHH the unicode char with value HHHHHHHH, in hexadecimal
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| 243 |
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| 244 | Also:
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| 245 |
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| 246 | \" Double quote.
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| 247 |
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| 248 | Inconsistent octal escapes:
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| 249 |
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| 250 | \0NNN echo -e '\0123'
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| 251 | \NNN printf '\123'
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| 252 | echo $'\123'
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| 253 |
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| 254 | TODO: Verify other differences between `echo -e`, `printf`, and `$''`. See
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| 255 | `frontend/lexer_def.py`.
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| 256 |
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