| 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 | ### char-literal
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| 90 |
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| 91 | Three kinds of unquoted backslash escapes are allowed in expression mode. They
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| 92 | match what's available in quoted J8-style strings:
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| 93 |
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| 94 | var backslash = \\
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| 95 | var quotes = \' ++ \" # same as u'\'' ++ '"'
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| 96 |
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| 97 | var mu = \u{3bc} # same as u'\u{3bc}'
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| 98 |
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| 99 | var nul = \y00 # same as b'\y00'
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| 100 |
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| 101 | ### ysh-string
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| 102 |
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| 103 | YSH has single and double-quoted strings borrowed from Bourne shell, and
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| 104 | C-style strings borrowed from J8 Notation.
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| 105 |
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| 106 | Double quoted strings respect `$` interpolation:
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| 107 |
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| 108 | var dq = "hello $world and $(hostname)"
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| 109 |
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| 110 | You can add a `$` before the left quote to be explicit: `$"x is $x"` rather
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| 111 | than `"x is $x"`.
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| 112 |
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| 113 | Single quoted strings may be raw:
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| 114 |
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| 115 | var s = r'line\n' # raw string means \n is literal, NOT a newline
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| 116 |
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| 117 | Or *J8 strings* with backslash escapes:
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| 118 |
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| 119 | var s = u'line\n \u{3bc}' # unicode string means \n is a newline
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| 120 | var s = b'line\n \u{3bc} \yff' # same thing, but also allows bytes
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| 121 |
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| 122 | Both `u''` and `b''` strings evaluate to the single `Str` type. The difference
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| 123 | is that `b''` strings allow the `\yff` byte escape.
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| 124 |
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| 125 | #### Notes
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| 126 |
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| 127 | There's no way to express a single quote in raw strings. Use one of the other
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| 128 | forms instead:
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| 129 |
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| 130 | var sq = "single quote: ' "
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| 131 | var sq = u'single quote: \' '
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| 132 |
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| 133 | Sometimes you can omit the `r`, e.g. where there are no backslashes and thus no
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| 134 | ambiguity:
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| 135 |
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| 136 | echo 'foo'
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| 137 | echo r'foo' # same thing
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| 138 |
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| 139 | The `u''` and `b''` strings are called *J8 strings* because the syntax in YSH
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| 140 | **code** matches JSON-like **data**.
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| 141 |
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| 142 | var strU = u'mu = \u{3bc}' # J8 string with escapes
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| 143 | var strB = b'bytes \yff' # J8 string that can express byte strings
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| 144 |
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| 145 | More examples:
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| 146 |
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| 147 | var myRaw = r'[a-z]\n' # raw strings can be used for regexes (not
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| 148 | # eggexes)
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| 149 |
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| 150 | ### triple-quoted
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| 151 |
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| 152 | Triple-quoted string literals have leading whitespace stripped on each line.
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| 153 | They come in the same variants:
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| 154 |
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| 155 | var dq = """
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| 156 | hello $world and $(hostname)
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| 157 | no leading whitespace
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| 158 | """
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| 159 |
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| 160 | var myRaw = r'''
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| 161 | raw string
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| 162 | no leading whitespace
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| 163 | '''
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| 164 |
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| 165 | var strU = u'''
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| 166 | string that happens to be unicode \u{3bc}
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| 167 | no leading whitespace
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| 168 | '''
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| 169 |
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| 170 | var strB = b'''
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| 171 | string that happens to be bytes \u{3bc} \yff
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| 172 | no leading whitespace
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| 173 | '''
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| 174 |
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| 175 | Again, you can omit the `r` prefix if there's no backslash, because it's not
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| 176 | ambiguous:
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| 177 |
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| 178 | var myRaw = '''
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| 179 | raw string
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| 180 | no leading whitespace
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| 181 | '''
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| 182 |
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| 183 | ### str-template
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| 184 |
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| 185 | String templates use the same syntax as double-quoted strings:
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| 186 |
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| 187 | var mytemplate = ^"name = $name, age = $age"
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| 188 |
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| 189 | Related topics:
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| 190 |
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| 191 | - [Str => replace](chap-type-method.html#replace)
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| 192 | - [ysh-string](chap-expr-lang.html#ysh-string)
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| 193 |
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| 194 | ### list-literal
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| 195 |
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| 196 | Lists have a Python-like syntax:
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| 197 |
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| 198 | var mylist = ['one', 'two', [42, 43]]
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| 199 |
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| 200 | And a shell-like syntax:
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| 201 |
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| 202 | var list2 = :| one two |
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| 203 |
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| 204 | The shell-like syntax accepts the same syntax as a simple command:
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| 205 |
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| 206 | ls $mystr @ARGV *.py {foo,bar}@example.com
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| 207 |
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| 208 | # Rather than executing ls, evaluate words into a List
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| 209 | var cmd = :| ls $mystr @ARGV *.py {foo,bar}@example.com |
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| 210 |
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| 211 | ### dict-literal
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| 212 |
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| 213 | Dicts look like JavaScript.
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| 214 |
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| 215 | var d = {
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| 216 | key1: 'value', # key can be unquoted if it looks like a var name
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| 217 | 'key2': 42, # or quote it
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| 218 |
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| 219 | ['key2' ++ suffix]: 43, # bracketed expression
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| 220 | }
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| 221 |
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| 222 | Omitting a value means that the corresponding key takes the value of a var of
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| 223 | the same name:
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| 224 |
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| 225 | ysh$ var x = 42
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| 226 | ysh$ var y = 43
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| 227 |
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| 228 | ysh$ var d = {x, y} # values omitted
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| 229 | ysh$ = d
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| 230 | (Dict) {x: 42, y: 43}
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| 231 |
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| 232 | ### range
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| 233 |
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| 234 | A range is a sequence of numbers that can be iterated over:
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| 235 |
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| 236 | for i in (0 .. 3) {
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| 237 | echo $i
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| 238 | }
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| 239 | => 0
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| 240 | => 1
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| 241 | => 2
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| 242 |
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| 243 | As with slices, the last number isn't included. To iterate from 1 to n, you
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| 244 | can use this idiom:
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| 245 |
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| 246 | for i in (1 .. n+1) {
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| 247 | echo $i
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| 248 | }
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| 249 |
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| 250 | ### block-expr
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| 251 |
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| 252 | In YSH expressions, we use `^()` to create a [Command][] object:
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| 253 |
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| 254 | var myblock = ^(echo $PWD; ls *.txt)
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| 255 |
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| 256 | It's more common for [Command][] objects to be created with block arguments,
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| 257 | which are not expressions:
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| 258 |
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| 259 | cd /tmp {
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| 260 | echo $PWD
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| 261 | ls *.txt
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| 262 | }
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| 263 |
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| 264 | [Command]: chap-type-method.html#Command
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| 265 |
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| 266 | ### expr-literal
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| 267 |
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| 268 | An expression literal is an object that holds an unevaluated expression:
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| 269 |
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| 270 | var myexpr = ^[1 + 2*3]
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| 271 |
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| 272 | [Expr]: chap-type-method.html#Expr
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| 273 |
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| 274 | ## Operators
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| 275 |
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| 276 | ### op-precedence
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| 277 |
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| 278 | YSH operator precedence is identical to Python's operator precedence.
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| 279 |
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| 280 | New operators:
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| 281 |
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| 282 | - `++` has the same precedence as `+`
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| 283 | - `->` and `=>` have the same precedence as `.`
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| 284 |
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| 285 | <!-- TODO: show grammar -->
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| 286 |
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| 287 |
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| 288 | <h3 id="concat">concat <code>++</code></h3>
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| 289 |
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| 290 | The concatenation operator works on `Str` objects:
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| 291 |
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| 292 | ysh$ var s = 'hello'
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| 293 | ysh$ var t = s ++ ' world'
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| 294 |
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| 295 | ysh$ = t
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| 296 | (Str) "hello world"
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| 297 |
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| 298 | and `List` objects:
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| 299 |
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| 300 | ysh$ var L = ['one', 'two']
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| 301 | ysh$ var M = L ++ ['three', '4']
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| 302 |
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| 303 | ysh$ = M
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| 304 | (List) ["one", "two", "three", "4"]
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| 305 |
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| 306 | String interpolation can be nicer than `++`:
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| 307 |
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| 308 | var t2 = "${s} world" # same as t
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| 309 |
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| 310 | Likewise, splicing lists can be nicer:
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| 311 |
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| 312 | var M2 = :| @L three 4 | # same as M
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| 313 |
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| 314 | ### ysh-equals
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| 315 |
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| 316 | YSH has strict equality:
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| 317 |
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| 318 | a === b # Python-like, without type conversion
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| 319 | a !== b # negated
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| 320 |
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| 321 | And type converting equality:
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| 322 |
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| 323 | '3' ~== 3 # True, type conversion
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| 324 |
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| 325 | The `~==` operator expects a string as the left operand.
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| 326 |
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| 327 | ---
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| 328 |
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| 329 | Note that:
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| 330 |
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| 331 | - `3 === 3.0` is false because integers and floats are different types, and
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| 332 | there is no type conversion.
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| 333 | - `3 ~== 3.0` is an error, because the left operand isn't a string.
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| 334 |
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| 335 | You may want to use explicit `int()` and `float()` to convert numbers, and then
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| 336 | compare them.
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| 337 |
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| 338 | ---
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| 339 |
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| 340 | Compare objects for identity with `is`:
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| 341 |
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| 342 | ysh$ var d = {}
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| 343 | ysh$ var e = d
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| 344 |
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| 345 | ysh$ = d is d
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| 346 | (Bool) true
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| 347 |
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| 348 | ysh$ = d is {other: 'dict'}
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| 349 | (Bool) false
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| 350 |
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| 351 | To negate `is`, use `is not` (like Python:
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| 352 |
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| 353 | ysh$ d is not {other: 'dict'}
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| 354 | (Bool) true
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| 355 |
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| 356 | ### ysh-in
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| 357 |
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| 358 | The `in` operator tests if a key is in a dictionary:
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| 359 |
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| 360 | var d = {k: 42}
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| 361 | if ('k' in d) {
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| 362 | echo yes
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| 363 | } # => yes
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| 364 |
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| 365 | Unlike Python, `in` doesn't work on `Str` and `List` instances. This because
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| 366 | those operations take linear time rather than constant time (O(n) rather than
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| 367 | O(1)).
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| 368 |
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| 369 | TODO: Use `includes() / contains()` methods instead.
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| 370 |
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| 371 | ### ysh-compare
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| 372 |
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| 373 | The comparison operators apply to integers or floats:
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| 374 |
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| 375 | 4 < 4 # => false
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| 376 | 4 <= 4 # => true
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| 377 |
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| 378 | 5.0 > 5.0 # => false
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| 379 | 5.0 >= 5.0 # => true
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| 380 |
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| 381 | Example in context:
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| 382 |
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| 383 | if (x < 0) {
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| 384 | echo 'x is negative'
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| 385 | }
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| 386 |
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| 387 | ### ysh-logical
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| 388 |
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| 389 | The logical operators take boolean operands, and are spelled like Python:
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| 390 |
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| 391 | not
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| 392 | and or
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| 393 |
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| 394 | Note that they are distinct from `! && ||`, which are part of the [command
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| 395 | language](chap-cmd-lang.html).
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| 396 |
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| 397 | ### ysh-arith
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| 398 |
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| 399 | YSH supports most of the arithmetic operators from Python. Notably, `/` and `%`
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| 400 | differ from Python as [they round toward zero, not negative
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| 401 | 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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| 402 |
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| 403 | Use `+ - *` for `Int` or `Float` addition, subtraction and multiplication. If
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| 404 | any of the operands are `Float`s, then the output will also be a `Float`.
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| 405 |
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| 406 | Use `/` and `//` for `Float` division and `Int` division, respectively. `/`
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| 407 | will _always_ result in a `Float`, meanwhile `//` will _always_ result in an
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| 408 | `Int`.
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| 409 |
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| 410 | = 1 / 2 # => (Float) 0.5
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| 411 | = 1 // 2 # => (Int) 0
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| 412 |
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| 413 | Use `%` to compute the _remainder_ of integer division. The left operand must
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| 414 | be an `Int` and the right a _positive_ `Int`.
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| 415 |
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| 416 | = 1 % 2 # -> (Int) 1
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| 417 | = -4 % 2 # -> (Int) 0
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| 418 |
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| 419 | Use `**` for exponentiation. The left operand must be an `Int` and the right a
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| 420 | _positive_ `Int`.
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| 421 |
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| 422 | All arithmetic operators may coerce either of their operands from strings to a
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| 423 | number, provided those strings are formatted as numbers.
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| 424 |
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| 425 | = 10 + '1' # => (Int) 11
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| 426 |
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| 427 | Operators like `+ - * /` will coerce strings to _either_ an `Int` or `Float`.
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| 428 | However, operators like `// ** %` and bit shifts will coerce strings _only_ to
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| 429 | an `Int`.
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| 430 |
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| 431 | = '1.14' + '2' # => (Float) 3.14
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| 432 | = '1.14' % '2' # Type Error: Left operand is a Str
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| 433 |
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| 434 | ### ysh-bitwise
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| 435 |
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| 436 | Bitwise operators are like Python and C:
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| 437 |
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| 438 | ~ # unary complement
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| 439 |
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| 440 | & | ^ # binary and, or, xor
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| 441 |
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| 442 | >> << # bit shift
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| 443 |
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| 444 | ### ysh-ternary
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| 445 |
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| 446 | The ternary operator is borrowed from Python:
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| 447 |
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| 448 | display = 'yes' if len(s) else 'empty'
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| 449 |
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| 450 | ### ysh-index
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| 451 |
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| 452 | `Str` objects can be indexed by byte:
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| 453 |
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| 454 | ysh$ var s = 'cat'
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| 455 | ysh$ = mystr[1]
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| 456 | (Str) 'a'
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| 457 |
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| 458 | ysh$ = mystr[-1] # index from the end
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| 459 | (Str) 't'
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| 460 |
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| 461 | `List` objects:
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| 462 |
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| 463 | ysh$ var mylist = [1, 2, 3]
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| 464 | ysh$ = mylist[2]
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| 465 | (Int) 3
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| 466 |
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| 467 | `Dict` objects are indexed by string key:
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| 468 |
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| 469 | ysh$ var mydict = {'key': 42}
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| 470 | ysh$ = mydict['key']
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| 471 | (Int) 42
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| 472 |
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| 473 | ### ysh-attr
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| 474 |
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| 475 | The expression `mydict.key` is short for `mydict['key']`.
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| 476 |
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| 477 | (Like JavaScript, but unlike Python.)
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| 478 |
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| 479 | ### ysh-slice
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| 480 |
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| 481 | Slicing gives you a subsequence of a `Str` or `List`, as in Python.
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| 482 |
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| 483 | Negative indices are relative to the end.
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| 484 |
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| 485 | String example:
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| 486 |
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| 487 | $ var s = 'spam eggs'
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| 488 | $ pp line (s[1:-1])
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| 489 | (Str) "pam egg"
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| 490 |
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| 491 | $ echo "x $[s[2:]]"
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| 492 | x am eggs
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| 493 |
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| 494 | List example:
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| 495 |
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| 496 | $ var foods = ['ale', 'bean', 'corn']
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| 497 | $ pp line (foods[-2:])
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| 498 | (List) ["bean","corn"]
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| 499 |
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| 500 | $ write -- @[foods[:2]]
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| 501 | ale
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| 502 | bean
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| 503 |
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| 504 | ### func-call
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| 505 |
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| 506 | A function call expression looks like Python:
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| 507 |
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| 508 | ysh$ = f('s', 't', named=42)
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| 509 |
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| 510 | A semicolon `;` can be used after positional args and before named args, but
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| 511 | isn't always required:
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| 512 |
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| 513 | ysh$ = f('s', 't'; named=42)
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| 514 |
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| 515 | In these cases, the `;` is necessary:
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| 516 |
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| 517 | ysh$ = f(...args; ...kwargs)
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| 518 |
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| 519 | ysh$ = f(42, 43; ...kwargs)
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| 520 |
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| 521 | ### thin-arrow
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| 522 |
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| 523 | The thin arrow is for mutating methods:
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| 524 |
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| 525 | var mylist = ['bar']
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| 526 | call mylist->pop()
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| 527 |
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| 528 | <!--
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| 529 | TODO
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| 530 | var mydict = {name: 'foo'}
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| 531 | call mydict->erase('name')
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| 532 | -->
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| 533 |
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| 534 | ### fat-arrow
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| 535 |
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| 536 | The fat arrow is for transforming methods:
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| 537 |
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| 538 | if (s => startsWith('prefix')) {
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| 539 | echo 'yes'
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| 540 | }
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| 541 |
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| 542 | If the method lookup on `s` fails, it looks for free functions. This means it
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| 543 | can be used for "chaining" transformations:
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| 544 |
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| 545 | var x = myFunc() => list() => join()
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| 546 |
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| 547 | ### match-ops
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| 548 |
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| 549 | YSH has four pattern matching operators: `~ !~ ~~ !~~`.
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| 550 |
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| 551 | Does string match an **eggex**?
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| 552 |
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| 553 | var filename = 'x42.py'
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| 554 | if (filename ~ / d+ /) {
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| 555 | echo 'number'
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| 556 | }
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| 557 |
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| 558 | Does a string match a POSIX regular expression (ERE syntax)?
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| 559 |
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| 560 | if (filename ~ '[[:digit:]]+') {
|
| 561 | echo 'number'
|
| 562 | }
|
| 563 |
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| 564 | Negate the result with the `!~` operator:
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| 565 |
|
| 566 | if (filename !~ /space/ ) {
|
| 567 | echo 'no space'
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| 568 | }
|
| 569 |
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| 570 | if (filename !~ '[[:space:]]' ) {
|
| 571 | echo 'no space'
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| 572 | }
|
| 573 |
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| 574 | Does a string match a **glob**?
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| 575 |
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| 576 | if (filename ~~ '*.py') {
|
| 577 | echo 'Python'
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| 578 | }
|
| 579 |
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| 580 | if (filename !~~ '*.py') {
|
| 581 | echo 'not Python'
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| 582 | }
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| 583 |
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| 584 | Take care not to confuse glob patterns and regular expressions.
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| 585 |
|
| 586 | - Related doc: [YSH Regex API](../ysh-regex-api.html)
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| 587 |
|
| 588 | ## Eggex
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| 589 |
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| 590 | ### re-literal
|
| 591 |
|
| 592 | An eggex literal looks like this:
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| 593 |
|
| 594 | / expression ; flags ; translation preference /
|
| 595 |
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| 596 | The flags and translation preference are both optional.
|
| 597 |
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| 598 | Examples:
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| 599 |
|
| 600 | var pat = / d+ / # => [[:digit:]]+
|
| 601 |
|
| 602 | You can specify flags passed to libc `regcomp()`:
|
| 603 |
|
| 604 | var pat = / d+ ; reg_icase reg_newline /
|
| 605 |
|
| 606 | You can specify a translation preference after a second semi-colon:
|
| 607 |
|
| 608 | var pat = / d+ ; ; ERE /
|
| 609 |
|
| 610 | Right now the translation preference does nothing. It could be used to
|
| 611 | translate eggex to PCRE or Python syntax.
|
| 612 |
|
| 613 | - Related doc: [Egg Expressions](../eggex.html)
|
| 614 |
|
| 615 | ### re-primitive
|
| 616 |
|
| 617 | There are two kinds of eggex primitives.
|
| 618 |
|
| 619 | "Zero-width assertions" match a position rather than a character:
|
| 620 |
|
| 621 | %start # translates to ^
|
| 622 | %end # translates to $
|
| 623 |
|
| 624 | Literal characters appear within **single** quotes:
|
| 625 |
|
| 626 | 'oh *really*' # translates to regex-escaped string
|
| 627 |
|
| 628 | Double-quoted strings are **not** eggex primitives. Instead, you can use
|
| 629 | splicing of strings:
|
| 630 |
|
| 631 | var dq = "hi $name"
|
| 632 | var eggex = / @dq /
|
| 633 |
|
| 634 | ### class-literal
|
| 635 |
|
| 636 | An eggex character class literal specifies a set. It can have individual
|
| 637 | characters and ranges:
|
| 638 |
|
| 639 | [ 'x' 'y' 'z' a-f A-F 0-9 ] # 3 chars, 3 ranges
|
| 640 |
|
| 641 | Omit quotes on ASCII characters:
|
| 642 |
|
| 643 | [ x y z ] # avoid typing 'x' 'y' 'z'
|
| 644 |
|
| 645 | Sets of characters can be written as strings
|
| 646 |
|
| 647 | [ 'xyz' ] # any of 3 chars, not a sequence of 3 chars
|
| 648 |
|
| 649 | Backslash escapes are respected:
|
| 650 |
|
| 651 | [ \\ \' \" \0 ]
|
| 652 | [ \xFF \u{3bc} ]
|
| 653 |
|
| 654 | (Note that we don't use `\yFF`, as in J8 strings.)
|
| 655 |
|
| 656 | Splicing:
|
| 657 |
|
| 658 | [ @str_var ]
|
| 659 |
|
| 660 | Negation always uses `!`
|
| 661 |
|
| 662 | ![ a-f A-F 'xyz' @str_var ]
|
| 663 |
|
| 664 | ### named-class
|
| 665 |
|
| 666 | Perl-like shortcuts for sets of characters:
|
| 667 |
|
| 668 | [ dot ] # => .
|
| 669 | [ digit ] # => [[:digit:]]
|
| 670 | [ space ] # => [[:space:]]
|
| 671 | [ word ] # => [[:alpha:]][[:digit:]]_
|
| 672 |
|
| 673 | Abbreviations:
|
| 674 |
|
| 675 | [ d s w ] # Same as [ digit space word ]
|
| 676 |
|
| 677 | Valid POSIX classes:
|
| 678 |
|
| 679 | alnum cntrl lower space
|
| 680 | alpha digit print upper
|
| 681 | blank graph punct xdigit
|
| 682 |
|
| 683 | Negated:
|
| 684 |
|
| 685 | !digit !space !word
|
| 686 | !d !s !w
|
| 687 | !alnum # etc.
|
| 688 |
|
| 689 | ### re-repeat
|
| 690 |
|
| 691 | Eggex repetition looks like POSIX syntax:
|
| 692 |
|
| 693 | / 'a'? / # zero or one
|
| 694 | / 'a'* / # zero or more
|
| 695 | / 'a'+ / # one or more
|
| 696 |
|
| 697 | Counted repetitions:
|
| 698 |
|
| 699 | / 'a'{3} / # exactly 3 repetitions
|
| 700 | / 'a'{2,4} / # between 2 to 4 repetitions
|
| 701 |
|
| 702 | ### re-compound
|
| 703 |
|
| 704 | Sequence expressions with a space:
|
| 705 |
|
| 706 | / word digit digit / # Matches 3 characters in sequence
|
| 707 | # Examples: a42, b51
|
| 708 |
|
| 709 | (Compare `/ [ word digit ] /`, which is a set matching 1 character.)
|
| 710 |
|
| 711 | Alternation with `|`:
|
| 712 |
|
| 713 | / word | digit / # Matches 'a' OR '9', for example
|
| 714 |
|
| 715 | Grouping with parentheses:
|
| 716 |
|
| 717 | / (word digit) | \\ / # Matches a9 or \
|
| 718 |
|
| 719 | ### re-capture
|
| 720 |
|
| 721 | To retrieve a substring of a string that matches an Eggex, use a "capture
|
| 722 | group" like `<capture ...>`.
|
| 723 |
|
| 724 | Here's an eggex with a **positional** capture:
|
| 725 |
|
| 726 | var pat = / 'hi ' <capture d+> / # access with _group(1)
|
| 727 | # or Match => _group(1)
|
| 728 |
|
| 729 | Captures can be **named**:
|
| 730 |
|
| 731 | <capture d+ as month> # access with _group('month')
|
| 732 | # or Match => group('month')
|
| 733 |
|
| 734 | Captures can also have a type **conversion func**:
|
| 735 |
|
| 736 | <capture d+ : int> # _group(1) returns Int
|
| 737 |
|
| 738 | <capture d+ as month: int> # _group('month') returns Int
|
| 739 |
|
| 740 | Related docs and help topics:
|
| 741 |
|
| 742 | - [YSH Regex API](../ysh-regex-api.html)
|
| 743 | - [`_group()`](chap-builtin-func.html#_group)
|
| 744 | - [`Match => group()`](chap-type-method.html#group)
|
| 745 |
|
| 746 | ### re-splice
|
| 747 |
|
| 748 | To build an eggex out of smaller expressions, you can **splice** eggexes
|
| 749 | together:
|
| 750 |
|
| 751 | var D = / [0-9][0-9] /
|
| 752 | var time = / @D ':' @D / # [0-9][0-9]:[0-9][0-9]
|
| 753 |
|
| 754 | If the variable begins with a capital letter, you can omit `@`:
|
| 755 |
|
| 756 | var ip = / D ':' D /
|
| 757 |
|
| 758 | You can also splice a string:
|
| 759 |
|
| 760 | var greeting = 'hi'
|
| 761 | var pat = / @greeting ' world' / # hi world
|
| 762 |
|
| 763 | Splicing is **not** string concatenation; it works on eggex subtrees.
|
| 764 |
|
| 765 | ### re-flags
|
| 766 |
|
| 767 | Valid ERE flags, which are passed to libc's `regcomp()`:
|
| 768 |
|
| 769 | - `reg_icase` aka `i` - ignore case
|
| 770 | - `reg_newline` - 4 matching changes related to newlines
|
| 771 |
|
| 772 | See `man regcomp`.
|
| 773 |
|
| 774 | ### re-multiline
|
| 775 |
|
| 776 | Multi-line eggexes aren't yet implemented. Splicing makes it less necessary:
|
| 777 |
|
| 778 | var Name = / <capture [a-z]+ as name> /
|
| 779 | var Num = / <capture d+ as num> /
|
| 780 | var Space = / <capture s+ as space> /
|
| 781 |
|
| 782 | # For variables named like CapWords, splicing @Name doesn't require @
|
| 783 | var lexer = / Name | Num | Space /
|