| 1 | ---
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| 2 | title: YSH Expression 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 **YSH Expression 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 YSH expression language, which includes [Egg
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| 17 | Expressions]($xref:eggex).
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| 18 |
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| 19 | <div id="dense-toc">
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| 20 | </div>
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| 21 |
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| 22 | ## Assignment
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| 23 |
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| 24 | ### assign
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| 25 |
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| 26 | The `=` operator is used with assignment keywords:
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| 27 |
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| 28 | var x = 42
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| 29 | setvar x = 43
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| 30 |
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| 31 | const y = 'k'
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| 32 |
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| 33 | setglobal z = 'g'
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| 34 |
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| 35 | ### aug-assign
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| 36 |
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| 37 | The augmented assignment operators are:
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| 38 |
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| 39 | += -= *= /= **= //= %=
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| 40 | &= |= ^= <<= >>=
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| 41 |
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| 42 | They are used with `setvar` and `setglobal`. For example:
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| 43 |
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| 44 | setvar x += 2
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| 45 |
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| 46 | is the same as:
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| 47 |
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| 48 | setvar x = x + 2
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| 49 |
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| 50 | Likewise, these are the same:
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| 51 |
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| 52 | setglobal a[i] -= 1
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| 53 |
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| 54 | setglobal a[i] = a[i] - 1
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| 55 |
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| 56 | ## Literals
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| 57 |
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| 58 | ### atom-literal
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| 59 |
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| 60 | YSH uses JavaScript-like spellings for these three "atoms":
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| 61 |
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| 62 | null # type Null
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| 63 | true false # type Bool
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| 64 |
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| 65 | Note: to signify "no value", you may sometimes use an empty string `''`,
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| 66 | instead of `null`.
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| 67 |
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| 68 | ### int-literal
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| 69 |
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| 70 | Examples of integer literals:
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| 71 |
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| 72 | var decimal = 42
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| 73 | var big = 42_000
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| 74 |
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| 75 | var hex = 0x0010_ffff
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| 76 |
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| 77 | var octal = 0o755
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| 78 |
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| 79 | var binary = 0b0001_0000
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| 80 |
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| 81 | ### float-lit
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| 82 |
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| 83 | Examples of float literals:
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| 84 |
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| 85 | var myfloat = 3.14
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| 86 |
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| 87 | var f2 = -1.5e-100
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| 88 |
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| 89 | ### ysh-string
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| 90 |
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| 91 | YSH has single and double-quoted strings borrowed from Bourne shell, and
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| 92 | C-style strings borrowed from J8 Notation.
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| 93 |
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| 94 | Double quoted strings respect `$` interpolation:
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| 95 |
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| 96 | var dq = "hello $world and $(hostname)"
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| 97 |
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| 98 | You can add a `$` before the left quote to be explicit: `$"x is $x"` rather
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| 99 | than `"x is $x"`.
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| 100 |
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| 101 | Single quoted strings may be raw:
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| 102 |
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| 103 | var s = r'line\n' # raw string means \n is literal, NOT a newline
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| 104 |
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| 105 | Or *J8 strings* with backslash escapes:
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| 106 |
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| 107 | var s = u'line\n \u{3bc}' # unicode string means \n is a newline
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| 108 | var s = b'line\n \u{3bc} \yff' # same thing, but also allows bytes
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| 109 |
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| 110 | Both `u''` and `b''` strings evaluate to the single `Str` type. The difference
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| 111 | is that `b''` strings allow the `\yff` byte escape.
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| 112 |
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| 113 | #### Notes
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| 114 |
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| 115 | There's no way to express a single quote in raw strings. Use one of the other
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| 116 | forms instead:
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| 117 |
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| 118 | var sq = "single quote: ' "
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| 119 | var sq = u'single quote: \' '
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| 120 |
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| 121 | Sometimes you can omit the `r`, e.g. where there are no backslashes and thus no
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| 122 | ambiguity:
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| 123 |
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| 124 | echo 'foo'
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| 125 | echo r'foo' # same thing
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| 126 |
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| 127 | The `u''` and `b''` strings are called *J8 strings* because the syntax in YSH
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| 128 | **code** matches JSON-like **data**.
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| 129 |
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| 130 | var strU = u'mu = \u{3bc}' # J8 string with escapes
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| 131 | var strB = b'bytes \yff' # J8 string that can express byte strings
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| 132 |
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| 133 | More examples:
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| 134 |
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| 135 | var myRaw = r'[a-z]\n' # raw strings can be used for regexes (not
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| 136 | # eggexes)
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| 137 |
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| 138 | ### triple-quoted
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| 139 |
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| 140 | Triple-quoted string literals have leading whitespace stripped on each line.
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| 141 | They come in the same variants:
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| 142 |
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| 143 | var dq = """
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| 144 | hello $world and $(hostname)
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| 145 | no leading whitespace
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| 146 | """
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| 147 |
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| 148 | var myRaw = r'''
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| 149 | raw string
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| 150 | no leading whitespace
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| 151 | '''
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| 152 |
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| 153 | var strU = u'''
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| 154 | string that happens to be unicode \u{3bc}
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| 155 | no leading whitespace
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| 156 | '''
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| 157 |
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| 158 | var strB = b'''
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| 159 | string that happens to be bytes \u{3bc} \yff
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| 160 | no leading whitespace
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| 161 | '''
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| 162 |
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| 163 | Again, you can omit the `r` prefix if there's no backslash, because it's not
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| 164 | ambiguous:
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| 165 |
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| 166 | var myRaw = '''
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| 167 | raw string
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| 168 | no leading whitespace
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| 169 | '''
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| 170 |
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| 171 | ### str-template
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| 172 |
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| 173 | String templates use the same syntax as double-quoted strings:
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| 174 |
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| 175 | var mytemplate = ^"name = $name, age = $age"
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| 176 |
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| 177 | Related topics:
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| 178 |
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| 179 | - [Str => replace](chap-type-method.html#replace)
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| 180 | - [ysh-string](chap-expr-lang.html#ysh-string)
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| 181 |
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| 182 | ### list-literal
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| 183 |
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| 184 | Lists have a Python-like syntax:
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| 185 |
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| 186 | var mylist = ['one', 'two', [42, 43]]
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| 187 |
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| 188 | And a shell-like syntax:
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| 189 |
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| 190 | var list2 = :| one two |
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| 191 |
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| 192 | The shell-like syntax accepts the same syntax as a simple command:
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| 193 |
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| 194 | ls $mystr @ARGV *.py {foo,bar}@example.com
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| 195 |
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| 196 | # Rather than executing ls, evaluate words into a List
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| 197 | var cmd = :| ls $mystr @ARGV *.py {foo,bar}@example.com |
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| 198 |
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| 199 | ### dict-literal
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| 200 |
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| 201 | Dicts look like JavaScript.
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| 202 |
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| 203 | var d = {
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| 204 | key1: 'value', # key can be unquoted if it looks like a var name
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| 205 | 'key2': 42, # or quote it
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| 206 |
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| 207 | ['key2' ++ suffix]: 43, # bracketed expression
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| 208 | }
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| 209 |
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| 210 | Omitting a value means that the corresponding key takes the value of a var of
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| 211 | the same name:
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| 212 |
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| 213 | ysh$ var x = 42
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| 214 | ysh$ var y = 43
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| 215 |
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| 216 | ysh$ var d = {x, y} # values omitted
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| 217 | ysh$ = d
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| 218 | (Dict) {x: 42, y: 43}
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| 219 |
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| 220 | ### range
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| 221 |
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| 222 | A range is a sequence of numbers that can be iterated over:
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| 223 |
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| 224 | for i in (0 .. 3) {
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| 225 | echo $i
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| 226 | }
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| 227 | => 0
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| 228 | => 1
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| 229 | => 2
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| 230 |
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| 231 | As with slices, the last number isn't included. To iterate from 1 to n, you
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| 232 | can use this idiom:
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| 233 |
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| 234 | for i in (1 .. n+1) {
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| 235 | echo $i
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| 236 | }
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| 237 |
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| 238 | ### block-expr
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| 239 |
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| 240 | In YSH expressions, we use `^()` to create a [Command][] object:
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| 241 |
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| 242 | var myblock = ^(echo $PWD; ls *.txt)
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| 243 |
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| 244 | It's more common for [Command][] objects to be created with block arguments,
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| 245 | which are not expressions:
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| 246 |
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| 247 | cd /tmp {
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| 248 | echo $PWD
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| 249 | ls *.txt
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| 250 | }
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| 251 |
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| 252 | [Command]: chap-type-method.html#Command
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| 253 |
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| 254 | ### expr-literal
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| 255 |
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| 256 | An expression literal is an object that holds an unevaluated expression:
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| 257 |
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| 258 | var myexpr = ^[1 + 2*3]
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| 259 |
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| 260 | [Expr]: chap-type-method.html#Expr
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| 261 |
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| 262 | ## Operators
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| 263 |
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| 264 | ### op-precedence
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| 265 |
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| 266 | YSH operator precedence is identical to Python's operator precedence.
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| 267 |
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| 268 | New operators:
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| 269 |
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| 270 | - `++` has the same precedence as `+`
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| 271 | - `->` and `=>` have the same precedence as `.`
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| 272 |
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| 273 | <!-- TODO: show grammar -->
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| 274 |
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| 275 |
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| 276 | <h3 id="concat">concat <code>++</code></h3>
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| 277 |
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| 278 | The concatenation operator works on `Str` objects:
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| 279 |
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| 280 | ysh$ var s = 'hello'
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| 281 | ysh$ var t = s ++ ' world'
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| 282 |
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| 283 | ysh$ = t
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| 284 | (Str) "hello world"
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| 285 |
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| 286 | and `List` objects:
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| 287 |
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| 288 | ysh$ var L = ['one', 'two']
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| 289 | ysh$ var M = L ++ ['three', '4']
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| 290 |
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| 291 | ysh$ = M
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| 292 | (List) ["one", "two", "three", "4"]
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| 293 |
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| 294 | String interpolation can be nicer than `++`:
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| 295 |
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| 296 | var t2 = "${s} world" # same as t
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| 297 |
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| 298 | Likewise, splicing lists can be nicer:
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| 299 |
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| 300 | var M2 = :| @L three 4 | # same as M
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| 301 |
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| 302 | ### ysh-equals
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| 303 |
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| 304 | YSH has strict equality:
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| 305 |
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| 306 | a === b # Python-like, without type conversion
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| 307 | a !== b # negated
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| 308 |
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| 309 | And type converting equality:
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| 310 |
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| 311 | '3' ~== 3 # True, type conversion
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| 312 |
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| 313 | The `~==` operator expects a string as the left operand.
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| 314 |
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| 315 | ---
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| 316 |
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| 317 | Note that:
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| 318 |
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| 319 | - `3 === 3.0` is false because integers and floats are different types, and
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| 320 | there is no type conversion.
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| 321 | - `3 ~== 3.0` is an error, because the left operand isn't a string.
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| 322 |
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| 323 | You may want to use explicit `int()` and `float()` to convert numbers, and then
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| 324 | compare them.
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| 325 |
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| 326 | ---
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| 327 |
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| 328 | Compare objects for identity with `is`:
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| 329 |
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| 330 | ysh$ var d = {}
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| 331 | ysh$ var e = d
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| 332 |
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| 333 | ysh$ = d is d
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| 334 | (Bool) true
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| 335 |
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| 336 | ysh$ = d is {other: 'dict'}
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| 337 | (Bool) false
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| 338 |
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| 339 | To negate `is`, use `is not` (like Python:
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| 340 |
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| 341 | ysh$ d is not {other: 'dict'}
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| 342 | (Bool) true
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| 343 |
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| 344 | ### ysh-in
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| 345 |
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| 346 | The `in` operator tests if a key is in a dictionary:
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| 347 |
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| 348 | var d = {k: 42}
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| 349 | if ('k' in d) {
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| 350 | echo yes
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| 351 | } # => yes
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| 352 |
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| 353 | Unlike Python, `in` doesn't work on `Str` and `List` instances. This because
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| 354 | those operations take linear time rather than constant time (O(n) rather than
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| 355 | O(1)).
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| 356 |
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| 357 | TODO: Use `includes() / contains()` methods instead.
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| 358 |
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| 359 | ### ysh-compare
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| 360 |
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| 361 | The comparison operators apply to integers or floats:
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| 362 |
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| 363 | 4 < 4 # => false
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| 364 | 4 <= 4 # => true
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| 365 |
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| 366 | 5.0 > 5.0 # => false
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| 367 | 5.0 >= 5.0 # => true
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| 368 |
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| 369 | Example in context:
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| 370 |
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| 371 | if (x < 0) {
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| 372 | echo 'x is negative'
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| 373 | }
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| 374 |
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| 375 | ### ysh-logical
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| 376 |
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| 377 | The logical operators take boolean operands, and are spelled like Python:
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| 378 |
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| 379 | not
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| 380 | and or
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| 381 |
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| 382 | Note that they are distinct from `! && ||`, which are part of the [command
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| 383 | language](chap-cmd-lang.html).
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| 384 |
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| 385 | ### ysh-arith
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| 386 |
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| 387 | YSH supports most of the arithmetic operators from Python. Notably, `/` and `%`
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| 388 | differ from Python as [they round toward zero, not negative
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| 389 | infinity](https://www.oilshell.org/blog/2024/03/release-0.21.0.html#integers-dont-do-whatever-python-or-c-does).
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| 390 |
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| 391 | Use `+ - *` for `Int` or `Float` addition, subtraction and multiplication. If
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| 392 | any of the operands are `Float`s, then the output will also be a `Float`.
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| 393 |
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| 394 | Use `/` and `//` for `Float` division and `Int` division, respectively. `/`
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| 395 | will _always_ result in a `Float`, meanwhile `//` will _always_ result in an
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| 396 | `Int`.
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| 397 |
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| 398 | = 1 / 2 # => (Float) 0.5
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| 399 | = 1 // 2 # => (Int) 0
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| 400 |
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| 401 | Use `%` to compute the _remainder_ of integer division. The left operand must
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| 402 | be an `Int` and the right a _positive_ `Int`.
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| 403 |
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| 404 | = 1 % 2 # -> (Int) 1
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| 405 | = -4 % 2 # -> (Int) 0
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| 406 |
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| 407 | Use `**` for exponentiation. The left operand must be an `Int` and the right a
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| 408 | _positive_ `Int`.
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| 409 |
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| 410 | All arithmetic operators may coerce either of their operands from strings to a
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| 411 | number, provided those strings are formatted as numbers.
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| 412 |
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| 413 | = 10 + '1' # => (Int) 11
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| 414 |
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| 415 | Operators like `+ - * /` will coerce strings to _either_ an `Int` or `Float`.
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| 416 | However, operators like `// ** %` and bit shifts will coerce strings _only_ to
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| 417 | an `Int`.
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| 418 |
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| 419 | = '1.14' + '2' # => (Float) 3.14
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| 420 | = '1.14' % '2' # Type Error: Left operand is a Str
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| 421 |
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| 422 | ### ysh-bitwise
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| 423 |
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| 424 | Bitwise operators are like Python and C:
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| 425 |
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| 426 | ~ # unary complement
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| 427 |
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| 428 | & | ^ # binary and, or, xor
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| 429 |
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| 430 | >> << # bit shift
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| 431 |
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| 432 | ### ysh-ternary
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| 433 |
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| 434 | The ternary operator is borrowed from Python:
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| 435 |
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| 436 | display = 'yes' if len(s) else 'empty'
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| 437 |
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| 438 | ### ysh-index
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| 439 |
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| 440 | `Str` objects can be indexed by byte:
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| 441 |
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| 442 | ysh$ var s = 'cat'
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| 443 | ysh$ = mystr[1]
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| 444 | (Str) 'a'
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| 445 |
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| 446 | ysh$ = mystr[-1] # index from the end
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| 447 | (Str) 't'
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| 448 |
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| 449 | `List` objects:
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| 450 |
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| 451 | ysh$ var mylist = [1, 2, 3]
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| 452 | ysh$ = mylist[2]
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| 453 | (Int) 3
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| 454 |
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| 455 | `Dict` objects are indexed by string key:
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| 456 |
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| 457 | ysh$ var mydict = {'key': 42}
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| 458 | ysh$ = mydict['key']
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| 459 | (Int) 42
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| 460 |
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| 461 | ### ysh-attr
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| 462 |
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| 463 | The expression `mydict.key` is short for `mydict['key']`.
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| 464 |
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| 465 | (Like JavaScript, but unlike Python.)
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| 466 |
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| 467 | ### ysh-slice
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| 468 |
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| 469 | Slicing gives you a subsequence of a `Str` or `List`, like Python.
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| 470 |
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| 471 | Negative indices are relative to the end.
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| 472 |
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| 473 | ### func-call
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| 474 |
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| 475 | A function call expression looks like Python:
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| 476 |
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| 477 | ysh$ = f('s', 't', named=42)
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| 478 |
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| 479 | A semicolon `;` can be used after positional args and before named args, but
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| 480 | isn't always required:
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| 481 |
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| 482 | ysh$ = f('s', 't'; named=42)
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| 483 |
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| 484 | In these cases, the `;` is necessary:
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| 485 |
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| 486 | ysh$ = f(...args; ...kwargs)
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| 487 |
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| 488 | ysh$ = f(42, 43; ...kwargs)
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| 489 |
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| 490 | ### thin-arrow
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| 491 |
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| 492 | The thin arrow is for mutating methods:
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| 493 |
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| 494 | var mylist = ['bar']
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| 495 | call mylist->pop()
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| 496 |
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| 497 | <!--
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| 498 | TODO
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| 499 | var mydict = {name: 'foo'}
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| 500 | call mydict->erase('name')
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| 501 | -->
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| 502 |
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| 503 | ### fat-arrow
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| 504 |
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| 505 | The fat arrow is for transforming methods:
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| 506 |
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| 507 | if (s => startsWith('prefix')) {
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| 508 | echo 'yes'
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| 509 | }
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| 510 |
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| 511 | If the method lookup on `s` fails, it looks for free functions. This means it
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| 512 | can be used for "chaining" transformations:
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| 513 |
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| 514 | var x = myFunc() => list() => join()
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| 515 |
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| 516 | ### match-ops
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| 517 |
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| 518 | YSH has four pattern matching operators: `~ !~ ~~ !~~`.
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| 519 |
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| 520 | Does string match an **eggex**?
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| 521 |
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| 522 | var filename = 'x42.py'
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| 523 | if (filename ~ / d+ /) {
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| 524 | echo 'number'
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| 525 | }
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| 526 |
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| 527 | Does a string match a POSIX regular expression (ERE syntax)?
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| 528 |
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| 529 | if (filename ~ '[[:digit:]]+') {
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| 530 | echo 'number'
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| 531 | }
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| 532 |
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| 533 | Negate the result with the `!~` operator:
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| 534 |
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| 535 | if (filename !~ /space/ ) {
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| 536 | echo 'no space'
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| 537 | }
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| 538 |
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| 539 | if (filename !~ '[[:space:]]' ) {
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| 540 | echo 'no space'
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| 541 | }
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| 542 |
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| 543 | Does a string match a **glob**?
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| 544 |
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| 545 | if (filename ~~ '*.py') {
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| 546 | echo 'Python'
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| 547 | }
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| 548 |
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| 549 | if (filename !~~ '*.py') {
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| 550 | echo 'not Python'
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| 551 | }
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| 552 |
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| 553 | Take care not to confuse glob patterns and regular expressions.
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| 554 |
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| 555 | - Related doc: [YSH Regex API](../ysh-regex-api.html)
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| 556 |
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| 557 | ## Eggex
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| 558 |
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| 559 | ### re-literal
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| 560 |
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| 561 | An eggex literal looks like this:
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| 562 |
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| 563 | / expression ; flags ; translation preference /
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| 564 |
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| 565 | The flags and translation preference are both optional.
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| 566 |
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| 567 | Examples:
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| 568 |
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| 569 | var pat = / d+ / # => [[:digit:]]+
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| 570 |
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| 571 | You can specify flags passed to libc `regcomp()`:
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| 572 |
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| 573 | var pat = / d+ ; reg_icase reg_newline /
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| 574 |
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| 575 | You can specify a translation preference after a second semi-colon:
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| 576 |
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| 577 | var pat = / d+ ; ; ERE /
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| 578 |
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| 579 | Right now the translation preference does nothing. It could be used to
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| 580 | translate eggex to PCRE or Python syntax.
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| 581 |
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| 582 | - Related doc: [Egg Expressions](../eggex.html)
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| 583 |
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| 584 | ### re-primitive
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| 585 |
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| 586 | There are two kinds of eggex primitives.
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| 587 |
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| 588 | "Zero-width assertions" match a position rather than a character:
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| 589 |
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| 590 | %start # translates to ^
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| 591 | %end # translates to $
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| 592 |
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| 593 | Literal characters appear within **single** quotes:
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| 594 |
|
| 595 | 'oh *really*' # translates to regex-escaped string
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| 596 |
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| 597 | Double-quoted strings are **not** eggex primitives. Instead, you can use
|
| 598 | splicing of strings:
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| 599 |
|
| 600 | var dq = "hi $name"
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| 601 | var eggex = / @dq /
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| 602 |
|
| 603 | ### class-literal
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| 604 |
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| 605 | An eggex character class literal specifies a set. It can have individual
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| 606 | characters and ranges:
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| 607 |
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| 608 | [ 'x' 'y' 'z' a-f A-F 0-9 ] # 3 chars, 3 ranges
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| 609 |
|
| 610 | Omit quotes on ASCII characters:
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| 611 |
|
| 612 | [ x y z ] # avoid typing 'x' 'y' 'z'
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| 613 |
|
| 614 | Sets of characters can be written as strings
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| 615 |
|
| 616 | [ 'xyz' ] # any of 3 chars, not a sequence of 3 chars
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| 617 |
|
| 618 | Backslash escapes are respected:
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| 619 |
|
| 620 | [ \\ \' \" \0 ]
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| 621 | [ \xFF \u0100 ]
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| 622 |
|
| 623 | Splicing:
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| 624 |
|
| 625 | [ @str_var ]
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| 626 |
|
| 627 | Negation always uses `!`
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| 628 |
|
| 629 | ![ a-f A-F 'xyz' @str_var ]
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| 630 |
|
| 631 | ### named-class
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| 632 |
|
| 633 | Perl-like shortcuts for sets of characters:
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| 634 |
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| 635 | [ dot ] # => .
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| 636 | [ digit ] # => [[:digit:]]
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| 637 | [ space ] # => [[:space:]]
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| 638 | [ word ] # => [[:alpha:]][[:digit:]]_
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| 639 |
|
| 640 | Abbreviations:
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| 641 |
|
| 642 | [ d s w ] # Same as [ digit space word ]
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| 643 |
|
| 644 | Valid POSIX classes:
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| 645 |
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| 646 | alnum cntrl lower space
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| 647 | alpha digit print upper
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| 648 | blank graph punct xdigit
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| 649 |
|
| 650 | Negated:
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| 651 |
|
| 652 | !digit !space !word
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| 653 | !d !s !w
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| 654 | !alnum # etc.
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| 655 |
|
| 656 | ### re-repeat
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| 657 |
|
| 658 | Eggex repetition looks like POSIX syntax:
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| 659 |
|
| 660 | / 'a'? / # zero or one
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| 661 | / 'a'* / # zero or more
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| 662 | / 'a'+ / # one or more
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| 663 |
|
| 664 | Counted repetitions:
|
| 665 |
|
| 666 | / 'a'{3} / # exactly 3 repetitions
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| 667 | / 'a'{2,4} / # between 2 to 4 repetitions
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| 668 |
|
| 669 | ### re-compound
|
| 670 |
|
| 671 | Sequence expressions with a space:
|
| 672 |
|
| 673 | / word digit digit / # Matches 3 characters in sequence
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| 674 | # Examples: a42, b51
|
| 675 |
|
| 676 | (Compare `/ [ word digit ] /`, which is a set matching 1 character.)
|
| 677 |
|
| 678 | Alternation with `|`:
|
| 679 |
|
| 680 | / word | digit / # Matches 'a' OR '9', for example
|
| 681 |
|
| 682 | Grouping with parentheses:
|
| 683 |
|
| 684 | / (word digit) | \\ / # Matches a9 or \
|
| 685 |
|
| 686 | ### re-capture
|
| 687 |
|
| 688 | To retrieve a substring of a string that matches an Eggex, use a "capture
|
| 689 | group" like `<capture ...>`.
|
| 690 |
|
| 691 | Here's an eggex with a **positional** capture:
|
| 692 |
|
| 693 | var pat = / 'hi ' <capture d+> / # access with _group(1)
|
| 694 | # or Match => _group(1)
|
| 695 |
|
| 696 | Captures can be **named**:
|
| 697 |
|
| 698 | <capture d+ as month> # access with _group('month')
|
| 699 | # or Match => group('month')
|
| 700 |
|
| 701 | Captures can also have a type **conversion func**:
|
| 702 |
|
| 703 | <capture d+ : int> # _group(1) returns Int
|
| 704 |
|
| 705 | <capture d+ as month: int> # _group('month') returns Int
|
| 706 |
|
| 707 | Related docs and help topics:
|
| 708 |
|
| 709 | - [YSH Regex API](../ysh-regex-api.html)
|
| 710 | - [`_group()`](chap-builtin-func.html#_group)
|
| 711 | - [`Match => group()`](chap-type-method.html#group)
|
| 712 |
|
| 713 | ### re-splice
|
| 714 |
|
| 715 | To build an eggex out of smaller expressions, you can **splice** eggexes
|
| 716 | together:
|
| 717 |
|
| 718 | var D = / [0-9][0-9] /
|
| 719 | var time = / @D ':' @D / # [0-9][0-9]:[0-9][0-9]
|
| 720 |
|
| 721 | If the variable begins with a capital letter, you can omit `@`:
|
| 722 |
|
| 723 | var ip = / D ':' D /
|
| 724 |
|
| 725 | You can also splice a string:
|
| 726 |
|
| 727 | var greeting = 'hi'
|
| 728 | var pat = / @greeting ' world' / # hi world
|
| 729 |
|
| 730 | Splicing is **not** string concatenation; it works on eggex subtrees.
|
| 731 |
|
| 732 | ### re-flags
|
| 733 |
|
| 734 | Valid ERE flags, which are passed to libc's `regcomp()`:
|
| 735 |
|
| 736 | - `reg_icase` aka `i` - ignore case
|
| 737 | - `reg_newline` - 4 matching changes related to newlines
|
| 738 |
|
| 739 | See `man regcomp`.
|
| 740 |
|
| 741 | ### re-multiline
|
| 742 |
|
| 743 | Multi-line eggexes aren't yet implemented. Splicing makes it less necessary:
|
| 744 |
|
| 745 | var Name = / <capture [a-z]+ as name> /
|
| 746 | var Num = / <capture d+ as num> /
|
| 747 | var Space = / <capture s+ as space> /
|
| 748 |
|
| 749 | # For variables named like CapWords, splicing @Name doesn't require @
|
| 750 | var lexer = / Name | Num | Space /
|