| 1 | ---
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| 2 | default_highlighter: oils-sh
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| 3 | in_progress: true
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| 4 | ---
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| 5 |
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| 6 | Strings: Quotes, Interpolation, Escaping, and Buffers
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| 7 | =====================================================
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| 8 |
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| 9 | Strings are the most important data structure in shell. YSH makes them easier
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| 10 | and safer!
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| 11 |
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| 12 | This doc addresses these questions:
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| 13 |
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| 14 | - How do you write different kinds of strings in YSH programs?
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| 15 | - How do they behave at runtime? What are the common operations?
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| 16 | - What are the recommended ways to use them?
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| 17 |
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| 18 | Shell Features:
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| 19 |
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| 20 | - Quotes (single or double quoted)
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| 21 | - Interpolation aka substitution (variable, command, etc.)
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| 22 |
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| 23 | YSH Features:
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| 24 |
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| 25 | - Escaping for safety: `${x|html}`, etc.
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| 26 | - Buffers for efficiency and readability: `${.myproc arg1}`, etc.
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| 27 | - (buffers are PHP-like)
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| 28 |
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| 29 | <div id="toc">
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| 30 | </div>
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| 31 |
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| 32 | ## Summary
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| 33 |
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| 34 | - YSH has three ways to write strings: single quoted, double quoted, and
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| 35 | C-style (which is also QSN-style).
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| 36 | - Each of the three types has a multiline variant. They are Python-style
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| 37 | triple-quoted, but they also strip leading space in an intelligent way.
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| 38 | - TODO: Tagged strings, like `"<h2>$x</h2>"html`
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| 39 | - TODO: For string safety, YSH adds the concept of "escapers" and interpolation
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| 40 | with `$[x]` (square brackets)
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| 41 | - TODO: For convenience and performance, YSH adds buffers and *builtin
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| 42 | substitution*: `${.myproc arg1}`.
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| 43 |
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| 44 | ### For Python/JS/C Users
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| 45 |
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| 46 | - Single and double quotes are different. Double quotes allow interpolation.
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| 47 | - Neither style of string respects backslash escapes like `\n` for newline.
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| 48 | You have to use the third form.
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| 49 |
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| 50 | ### For Shell Users
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| 51 |
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| 52 | - YSH replaces here docs with Python-style triple-quoted strings.
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| 53 |
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| 54 | Preferences:
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| 55 |
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| 56 | - Unquoted strings (command mode only)
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| 57 | - Single-quoted strings
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| 58 | - when you need to express special characters
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| 59 | - QSN
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| 60 | - Double-quoted strings
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| 61 | - with `$[]` interpolation
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| 62 | - with `${}` interpolation
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| 63 | - with fast command sub `${.myproc arg1}
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| 64 |
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| 65 | ### Quick Reference
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| 66 |
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| 67 | echo unquoted # bare words are allowed in command mode
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| 68 |
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| 69 | echo 'with spaces' # single quoted string
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| 70 | var s = 'with spaces'
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| 71 |
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| 72 | # Raw single quoted string, to emphasize literal backslashes
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| 73 | var s = r'C:\Program Files\'
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| 74 |
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| 75 | # C-escaped single quoted string
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| 76 | var line = $'foo\n'
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| 77 |
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| 78 | # double quoted with safe interpolation (TODO)
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| 79 | echo "<p>hello $[name]</p>" # default_escaper must be set
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| 80 | echo "<p>hello ${name|html}</p>" # explicit escaper
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| 81 |
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| 82 | # double quoted with unsafe interpolation
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| 83 | echo "hello $name"
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| 84 | echo "hello ${name}_suffix" # braces delimit variable name
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| 85 |
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| 86 | echo $(date +%x) # command sub
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| 87 |
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| 88 | Still TODO:
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| 89 |
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| 90 | echo ${.myproc arg1}
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| 91 |
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| 92 | cat <<< '''
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| 93 | one
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| 94 | two
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| 95 | '''
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| 96 |
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| 97 | cat <<< $'''
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| 98 | mu = \u{3bc}
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| 99 | nul = \x00
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| 100 | '''
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| 101 |
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| 102 | var s = """
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| 103 | multiline with ${vars}
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| 104 | $(date +%x)
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| 105 | ${.myproc arg1}
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| 106 | """
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| 107 |
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| 108 |
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| 109 | ## Use Unquoted Strings in Command Mode
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| 110 |
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| 111 | Shell is unique! You don't have to quote strings.
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| 112 |
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| 113 | - link: command vs. expression mode
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| 114 |
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| 115 | and quoted strings in expression mode
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| 116 |
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| 117 | ## Two Kinds of Single-Quoted Strings
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| 118 |
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| 119 | ### Raw with `r'C:\Program Files\'`
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| 120 |
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| 121 | - TODO: `parse_raw_strings`
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| 122 |
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| 123 | ### C-Escaped With `$'foo\n'`
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| 124 |
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| 125 | - Use the [QSN]($xref) subset
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| 126 |
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| 127 | ### QSN For *Data* Interchange
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| 128 |
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| 129 | TODO: explain the difference.
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| 130 |
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| 131 | This is different! It's data and not code. Analogy to JSON.
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| 132 |
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| 133 | - When you want represent any string on a single line (filenames)
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| 134 | - To make binary data readable
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| 135 | - To display data in a terminal (protect against terminal codes)
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| 136 |
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| 137 | ## Use Double-Quoted Strings For Interpolation
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| 138 |
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| 139 | ### Implicit Safe Interpolation with `$[x]` (TODO)
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| 140 |
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| 141 | - Use `$[x]` for safe interpolation
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| 142 | - Respects `shopt --set default_escaper`
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| 143 |
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| 144 | ### Explicit Safe Interpolation With `${x|html}` (TODO)
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| 145 |
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| 146 | - Use `${x|html}` for safe interpolation
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| 147 |
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| 148 | Note you can have bugs if you use the wrong escaper!
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| 149 |
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| 150 | ### Raw Interpolation with `$x` (may be unsafe)
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| 151 |
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| 152 | - Use `$x` or `${x}`
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| 153 | - These are identical except for syntax
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| 154 | - Useful for log messages, which aren't security sensitive
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| 155 |
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| 156 | Note that you should **not** use `"${var}"` in YSH code. Use `$var` or
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| 157 | `${var}` because of simple word evaluation.
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| 158 |
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| 159 | ### Command Sub `$(echo hi)`
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| 160 |
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| 161 | ### Fast Command Sub `${.myproc}` (stdout capture)
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| 162 |
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| 163 | Note that only words are allowed here; not full commands. Wrap other commands
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| 164 | in a proc.
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| 165 |
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| 166 | - Using `write_to_buffer`
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| 167 |
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| 168 | TODO:
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| 169 |
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| 170 | echo ${.myproc foo|html} # I think this should be supported
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| 171 |
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| 172 | ## Escapers / Codecs (TODO)
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| 173 |
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| 174 | For `${x|html}` and `${.myproc|html}`
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| 175 |
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| 176 | TODO
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| 177 |
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| 178 | - how to register them
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| 179 | - wasm plugins?
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| 180 |
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| 181 | ## Use Triple Quoted Strings Instead of Here Docs (TODO)
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| 182 |
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| 183 | TODO
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| 184 |
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| 185 | ## Concatenate With `"$str1$str2"`
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| 186 |
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| 187 | Or `"${str1}${str2}"`
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| 188 |
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| 189 | - is `s ++ t` valid?. It isn't necessary for strings and lists
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| 190 | - `:| @a @b |` is the same for lists
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| 191 | - does this Python syntax also work? `[*a, *b]`
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| 192 | - Dicts: `{d, **e}` might be better
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| 193 |
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| 194 | ### Avoid Concatenation in a Loop
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| 195 |
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| 196 | setvar s = "${s}${suffix}"
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| 197 |
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| 198 | ## Append with Two Styles
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| 199 |
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| 200 | Since there is no `++` operator, there is no `++=` operator.
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| 201 |
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| 202 | ### `echo`, `printf`, `write`, and `${.myproc}` (`write_to_buffer`)
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| 203 |
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| 204 | echo, printf, and write have their output captured.
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| 205 |
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| 206 | proc p(arg) {
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| 207 | ### A proc that has its output captured quickly.
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| 208 |
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| 209 | echo $arg
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| 210 | write two
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| 211 |
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| 212 | const x = 'three'
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| 213 | printf '%s\n' $x
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| 214 |
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| 215 | # newline for interactive testing, but not when captured
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| 216 | if ! shopt -q write_to_buffer {
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| 217 | echo
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| 218 | }
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| 219 | }
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| 220 |
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| 221 | echo ${.p one} # $'one\ntwo\nthree\n'
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| 222 |
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| 223 | ### `append` and `join`
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| 224 |
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| 225 | var buf = :| |
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| 226 | append 'one ' (buf)
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| 227 | append $'two\n' (buf)
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| 228 | echo $[join(buf)]
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| 229 |
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| 230 | ## Appendix A: Deprecated Shell Constructs
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| 231 |
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| 232 | - here docs!
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| 233 | - Use tripled quoted strings.
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| 234 | - Backticks for command sub
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| 235 | - Use `$(echo hi)`
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| 236 | - Arithmetic substitution like `$((1 + 2))`
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| 237 | - Use YSH expressions: `$[1 + 2]`
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| 238 | - `${x%%prefix}` and so forth
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| 239 | - Use builtin YSH functions (TODO)
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| 240 | - Unused: bash `$""` for localization?
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| 241 |
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| 242 | ## Appendix B: Related Documents
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| 243 |
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| 244 | - Simple Word Eval: you don't need quoting as much
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| 245 | - Expression Language
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| 246 | - [QSN](qsn.html)
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