| 1 | ---
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| 2 | default_highlighter: oils-sh
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| 3 | ---
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| 4 |
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| 5 | YSH Language Warts
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| 6 | ==================
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| 7 |
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| 8 | This documents describes parts of the YSH language that may be surprising.
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| 9 |
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| 10 | All languages have warts, but most of them don't document them for you! Even a
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| 11 | nice language like Python has surprising cases like `42,` and `f(x),` being a
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| 12 | 1-tuple (because of the trailing comma).
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| 13 |
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| 14 | The goal of YSH is to remove the many warts of shell, documented at [Shell
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| 15 | WTFs][wtfs]. Nonetheless it has some of its own.
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| 16 |
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| 17 | [wtfs]: https://github.com/oilshell/oil/wiki/Shell-WTFs
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| 18 |
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| 19 | <div id="toc">
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| 20 | </div>
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| 21 |
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| 22 | ## For Bash Compatibility
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| 23 |
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| 24 | ### Two Left Parens Should be Separated By Space
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| 25 |
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| 26 | No:
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| 27 |
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| 28 | if ((x + 1) < n) { # note ((
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| 29 | echo 'less'
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| 30 | }
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| 31 |
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| 32 | Yes:
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| 33 |
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| 34 | if ( (x + 1) < n) { # add a space
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| 35 | echo 'less'
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| 36 | }
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| 37 |
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| 38 | This is because the `((` token is for bash arithmetic, which is disallowed in
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| 39 | YSH.
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| 40 |
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| 41 | ### Two Different Syntaxes For `Block` and `Expr` Literals
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| 42 |
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| 43 | Blocks look different in command vs expression mode:
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| 44 |
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| 45 | cd /tmp { # command mode { }
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| 46 | echo $PWD
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| 47 | }
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| 48 | var myblock = ^(echo $PWD) # expression mode, lazy ^( )
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| 49 |
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| 50 | So do expressions:
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| 51 |
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| 52 | myproc | where (age > 10) # command mode, lazy ( )
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| 53 | var myval = age > 10 # expression mode
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| 54 | var myexpr = ^[age > 10] # expression mode, lazy ^[ ]
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| 55 |
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| 56 | It would have been nicer if they were consistent, but shell is already
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| 57 | inconsistent with `$(echo hi)` and `{ echo hi; }`.
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| 58 |
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| 59 | There is consistency in other directions:
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| 60 |
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| 61 | - `^(echo $PWD)` is consistent with shell's eagerly evaluated `$(echo $PWD)`.
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| 62 | - `^[42 + f(x)]` is consistent with expression sub `$[42 + f(x)]`.
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| 63 |
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| 64 | Most users won't see these literal forms very much. They're more useful for
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| 65 | testing and frameworks rather than simple scripts/applications.
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| 66 |
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| 67 | ## Related
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| 68 |
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| 69 | - The doc on [compatibility quirks](quirks.html) relates to the OSH language.
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| 70 |
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