| 1 | ---
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| 2 | title: Front End (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 **Front End**
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| 13 |
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| 14 | </div>
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| 15 |
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| 16 | This chapter describes command line usage and lexing.
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| 17 |
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| 18 | <span class="in-progress">(in progress)</span>
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| 19 |
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| 20 | <div id="dense-toc">
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| 21 | </div>
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| 22 |
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| 23 | <h2 id="usage">Command Line Usage</h3>
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| 24 |
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| 25 | <h3 id="oils-usage" class="osh-ysh-topic" oils-embed="1">
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| 26 | oils-usage
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| 27 | </h3>
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| 28 |
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| 29 | <!-- pre-formatted for help builtin -->
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| 30 |
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| 31 | ```
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| 32 | bin/oils-for-unix is an executable that contains OSH, YSH, and more.
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| 33 |
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| 34 | Usage: oils-for-unix MAIN_NAME ARG*
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| 35 | MAIN_NAME ARG*
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| 36 |
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| 37 | It behaves like busybox. The command name can be passed as the first argument:
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| 38 |
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| 39 | oils-for-unix ysh -c 'echo hi'
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| 40 |
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| 41 | More commonly, it's invoked through a symlink like 'ysh', which causes it to
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| 42 | behave like that command:
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| 43 |
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| 44 | ysh -c 'echo hi'
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| 45 |
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| 46 | ```
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| 47 |
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| 48 | <h3 id="osh-usage" class="osh-topic" oils-embed="1">
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| 49 | osh-usage
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| 50 | </h3>
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| 51 |
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| 52 | <!-- pre-formatted for help builtin -->
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| 53 |
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| 54 | ```
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| 55 | bin/osh is compatible with POSIX shell, bash, and other shells.
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| 56 |
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| 57 | Usage: osh FLAG* SCRIPT ARG*
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| 58 | osh FLAG* -c COMMAND ARG*
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| 59 | osh FLAG*
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| 60 |
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| 61 | The command line accepted by `bin/osh` is compatible with /bin/sh and bash.
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| 62 |
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| 63 | osh -c 'echo hi'
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| 64 | osh myscript.sh
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| 65 | echo 'echo hi' | osh
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| 66 |
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| 67 | It also has a few enhancements:
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| 68 |
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| 69 | osh -n -c 'hello' # pretty-print the AST
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| 70 | osh --ast-format text -n -c 'hello' # print it full
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| 71 |
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| 72 | osh accepts POSIX sh flags, with these additions:
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| 73 |
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| 74 | -n parse the program but don't execute it. Print the AST.
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| 75 | --ast-format what format the AST should be in
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| 76 | ```
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| 77 |
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| 78 | <h3 id="ysh-usage" class="ysh-topic" oils-embed="1">
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| 79 | ysh-usage
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| 80 | </h3>
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| 81 |
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| 82 | <!-- pre-formatted for help builtin -->
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| 83 |
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| 84 | ```
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| 85 | bin/ysh is the shell with data tYpes, influenced by pYthon, JavaScript, ...
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| 86 |
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| 87 | Usage: ysh FLAG* SCRIPT ARG*
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| 88 | ysh FLAG* -c COMMAND ARG*
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| 89 | ysh FLAG*
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| 90 |
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| 91 | `bin/ysh` is the same as `bin/osh` with a the `ysh:all` option group set. So
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| 92 | `bin/ysh` also accepts shell flags.
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| 93 |
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| 94 | ysh -c 'echo hi'
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| 95 | ysh myscript.ysh
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| 96 | echo 'echo hi' | ysh
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| 97 | ```
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| 98 |
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| 99 |
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| 100 | <h3 id="config" class="osh-ysh-topic">config</h3>
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| 101 |
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| 102 | If the --rcfile flag is specified, that file will be executed on startup.
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| 103 | Otherwise:
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| 104 |
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| 105 | - `bin/osh` runs `~/.config/oils/oshrc`
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| 106 | - `bin/ysh` runs `~/.config/oils/yshrc`
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| 107 |
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| 108 | Pass --rcfile /dev/null or --norc to disable the startup file.
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| 109 |
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| 110 | If the --rcdir flag is specified, files in that folder will be executed on
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| 111 | startup.
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| 112 | Otherwise:
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| 113 |
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| 114 | - `bin/osh` runs everything in `~/.config/oils/oshrc.d/`
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| 115 | - `bin/ysh` runs everything in `~/.config/oils/yshrc.d/`
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| 116 |
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| 117 | Pass --norc to disable the startup directory.
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| 118 |
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| 119 | <h3 id="startup" class="osh-ysh-topic">startup</h3>
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| 120 |
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| 121 | History is read?
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| 122 |
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| 123 | <h3 id="line-editing" class="osh-ysh-topic">line-editing</h3>
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| 124 |
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| 125 | Oils is often built with GNU readline, which recognizes many terminal commands
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| 126 | for editing input.
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| 127 |
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| 128 | A useful option is `set -o vi`, which tells GNU readline to accept vi keys.
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| 129 |
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| 130 | <h3 id="exit-codes" class="osh-ysh-topic">exit-codes</h3>
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| 131 |
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| 132 | The meaning of exit codes is a convention, and generally follows one of two
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| 133 | paradigms.
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| 134 |
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| 135 | #### The Success / Failure Paradigm
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| 136 |
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| 137 | - `0` for **success**.
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| 138 | - `1` for **runtime error**
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| 139 | - Example: `echo foo > out.txt` and `out.txt` can't be opened.
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| 140 | - Example: `fg` and there's not job to put in the foreground.
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| 141 | - `2` for **parse error**. This means that we didn't *attempt* to do
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| 142 | anything, rather than doing something, then it fails.
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| 143 | - Example: A language parse error, like `echo $(`.
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| 144 | - Example: Builtin usage error, like `read -z`.
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| 145 | - `3` for runtime **expression errors**. The expression language is new to
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| 146 | Oils, so its errors have a new exit code.
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| 147 | - Example: divide by zero `42 / 0`
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| 148 | - Example: index out of range `a[1000]`
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| 149 |
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| 150 | POSIX exit codes:
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| 151 |
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| 152 | - `126` for permission denied when running a command (`errno EACCES`)
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| 153 | - `127` for command not found
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| 154 |
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| 155 | Hint: Error checking often looks like this:
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| 156 |
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| 157 | try {
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| 158 | ls /bad
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| 159 | }
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| 160 | if (_status !== 0) {
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| 161 | echo 'failed'
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| 162 | }
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| 163 |
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| 164 | #### The Boolean Paradigm
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| 165 |
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| 166 | - `0` for **true**
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| 167 | - `1` for **false**.
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| 168 | - Example: `test -f foo` and `foo` isn't a file.
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| 169 | - `2` for **error** (usage error, parse error, etc.)
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| 170 | - Example: `test -q`: the flag isn't accepted.
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| 171 |
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| 172 | Hint: The `boolstatus` builtin ensures that false and error aren't confused:
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| 173 |
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| 174 | if boolstatus test -f foo {
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| 175 | echo 'foo exists'
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| 176 | }
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| 177 |
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| 178 | See [YSH Fixes Shell's Error Handling](../error-handling.html) for more detail.
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| 179 |
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| 180 | ## Lexing
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| 181 |
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| 182 | <h3 id="comment" class="osh-ysh-topic">comment</h3>
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| 183 |
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| 184 | A comment starts with `#` and goes until the end of the line.
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| 185 |
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| 186 | echo hi # print a greeting
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| 187 |
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| 188 | <h3 id="line-continuation" class="osh-ysh-topic">line-continuation</h3>
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| 189 |
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| 190 | A backslash `\` at the end of a line continues the line without executing it:
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| 191 |
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| 192 | ls /usr/bin \
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| 193 | /usr/lib \
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| 194 | ~/src # A single command split over three lines
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| 195 |
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| 196 | <h3 id="ascii-whitespace" class="osh-ysh-topic">ascii-whitespace</h3>
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| 197 |
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| 198 | In most places, Oils uses the same definition of ASCII whitespace as JSON.
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| 199 | That is, any of these 4 bytes are considered whitespace:
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| 200 |
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| 201 | [ \t\r\n] # space, tab, carriage return, newline
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| 202 |
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| 203 | Sometimes newlines are significant, e.g. after shell commands. Then the set of
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| 204 | whitespace characters is:
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| 205 |
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| 206 | [ \t\r]
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| 207 |
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| 208 | (We don't handle the Windows `\r\n` sequence in a special way. Instead, `\r`
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| 209 | is often treated like space and tab.)
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| 210 |
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| 211 | Examples:
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| 212 |
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| 213 | - Inside shell arithmetic `$(( 1 + 2 ))`, ASCII whitespace is ignored.
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| 214 | - Inside YSH expressions `42 + a[i] * f(x)`, ASCII whitespace is ignored.
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| 215 |
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| 216 | Exceptions:
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| 217 |
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| 218 | - Carriage return `\r` may not always be whitespace.
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| 219 | - It can appear in an unquoted shell words, a rule that all POSIX shells
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| 220 | follow.
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| 221 | - The default `$IFS` doesn't include `\r`.
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| 222 | - YSH `trim()` functions also respect Unicode space.
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| 223 |
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| 224 | <h3 id="ascii-control-chars" class="osh-ysh-topic">ascii-control-chars</h3>
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| 225 |
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| 226 | The ASCII control chars have byte values `0x00` to `0x1F`. This set includes 3
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| 227 | whitespace chars:
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| 228 |
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| 229 | - tab - `\t` aka `0x09`
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| 230 | - newline - `\n` aka `0x0a`
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| 231 | - carriage return - `\r` aka `0x0d`
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| 232 |
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| 233 | (It doesn't include the space - `0x20`.)
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| 234 |
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| 235 | General rules:
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| 236 |
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| 237 | - In J8 **data** languages, control chars other than whitespace are illegal.
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| 238 | This is consistent with the JSON spec.
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| 239 | - In **source code**, control chars are allowed (but discouraged).
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| 240 | - For example, in OSH, we don't check for control chars unquoted words
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| 241 | words or string literals. They are treated like printable chars.
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| 242 | - TODO: YSH should only allow printable characters, which implies valid
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| 243 | UTF-8.
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| 244 |
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| 245 | Note about `NUL` aka `0x00`:
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| 246 |
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| 247 | - The NUL byte is often used to terminate buffers, i.e. as a sentinel for
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| 248 | [re2c](https://re2c.org) lexing. This means that data after the NUL will be
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| 249 | ignored.
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| 250 | - J8 **data** input is read all at once, i.e. **not** split into lines. So
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| 251 | everything after the first NUL may be ignored.
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| 252 | - Shell **source code** is split into lines.
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| 253 |
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| 254 | <h3 id="doc-comment" class="ysh-topic">doc-comment</h3>
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| 255 |
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| 256 | Doc comments look like this:
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| 257 |
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| 258 | proc deploy {
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| 259 | ### Deploy the app
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| 260 | echo hi
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| 261 | }
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| 262 |
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| 263 | <h3 id="multiline-command" class="ysh-topic">multiline-command</h3>
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| 264 |
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| 265 | The ... prefix starts a single command over multiple lines. It allows writing
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| 266 | long commands without \ continuation lines, and the resulting limitations on
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| 267 | where you can put comments.
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| 268 |
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| 269 | Single command example:
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| 270 |
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| 271 | ... chromium-browser
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| 272 | # comment on its own line
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| 273 | --no-proxy-server
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| 274 | --incognito # comment to the right
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| 275 | ;
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| 276 |
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| 277 | Long pipelines and and-or chains:
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| 278 |
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| 279 | ... find .
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| 280 | # exclude tests
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| 281 | | grep -v '_test.py'
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| 282 | | xargs wc -l
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| 283 | | sort -n
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| 284 | ;
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| 285 |
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| 286 | ... ls /
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| 287 | && ls /bin
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| 288 | && ls /lib
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| 289 | || error "oops"
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| 290 | ;
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| 291 |
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| 292 | ## Tools
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| 293 |
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| 294 | ### cat-em
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| 295 |
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| 296 | Print files embedded in the `oils-for-unix` binary to stdout. Example:
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| 297 |
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| 298 | osh --tool cat-em stdlib/math.ysh stdlib/other.ysh
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| 299 |
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| 300 |
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| 301 | ## Help Chapters
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| 302 |
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| 303 | <h3 id="osh-chapters" class="osh-topic" oils-embed="1">
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| 304 | osh-chapters
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| 305 | </h3>
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| 306 |
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| 307 | <!-- shown at the bottom of 'help' -->
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| 308 |
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| 309 | ```
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| 310 | The reference is divided in to "chapters", each of which has its own table of
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| 311 | contents. Type:
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| 312 |
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| 313 | help osh-$CHAPTER
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| 314 |
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| 315 | Where $CHAPTER is one of:
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| 316 |
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| 317 | front-end
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| 318 | command-lang
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| 319 | osh-assign
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| 320 | word-lang
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| 321 | mini-lang
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| 322 | builtin-cmd
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| 323 | option
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| 324 | special-var
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| 325 | plugin
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| 326 |
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| 327 | Example:
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| 328 |
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| 329 | help osh-word-lang
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| 330 | ```
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| 331 |
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| 332 |
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| 333 | <h3 id="ysh-chapters" class="ysh-topic" oils-embed="1">
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| 334 | ysh-chapters
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| 335 | </h3>
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| 336 |
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| 337 | <!-- shown at the bottom of 'help' -->
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| 338 |
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| 339 | ```
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| 340 | The reference is divided in to "chapters", each of which has its own table of
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| 341 | contents. Type:
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| 342 |
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| 343 | help ysh-$CHAPTER
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| 344 |
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| 345 | Where $CHAPTER is one of:
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| 346 |
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| 347 | front-end
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| 348 | command-lang
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| 349 | expr-lang
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| 350 | word-lang
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| 351 | builtin-cmd
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| 352 | option
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| 353 | special-var
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| 354 | type-method
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| 355 | builtin-func
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| 356 |
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| 357 | Example:
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| 358 |
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| 359 | help ysh-expr-lang
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| 360 | ```
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| 361 |
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| 362 | <!-- h4 needed to end last card: ysh-chapters -->
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| 363 | <h4></h4>
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