| 1 | ---
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| 2 | title: Special Variables (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 **Special Variables**
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| 13 |
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| 14 | </div>
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| 15 |
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| 16 | This chapter describes special variables for OSH and YSH.
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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 | ## YSH Vars
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| 24 |
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| 25 | ### ARGV
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| 26 |
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| 27 | ARGV is List of strings contaning an argument array. This is the YSH
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| 28 | replacement for shell's `"$@"`.
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| 29 |
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| 30 | - At the top level, it contains the arguments passed to the shell.
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| 31 | - Inside an **open** [proc][], it contains the arguments passed to the proc.
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| 32 |
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| 33 | For example:
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| 34 |
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| 35 | proc p { # open proc, ARGV is swithout signature
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| 36 | echo @ARGV
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| 37 | }
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| 38 | p a b c # => a b c
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| 39 |
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| 40 | In contrast, inside a closed proc, `ARGV` is empty.
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| 41 |
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| 42 | proc p () { # closed proc
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| 43 | echo @ARGV
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| 44 | }
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| 45 |
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| 46 | [proc]: chap-ysh-cmd.html#proc
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| 47 |
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| 48 | ### ENV
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| 49 |
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| 50 | An `Obj` that's populated with environment variables. Example usage:
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| 51 |
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| 52 | var x = ENV.PYTHONPATH
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| 53 | echo $[ENV.SSH_AUTH_SOCK]
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| 54 | setglobal ENV.PYTHONPATH = '.'
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| 55 |
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| 56 | It's initialized exactly **once** per process, in any of these situations:
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| 57 |
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| 58 | 1. At shell startup, if `shopt --set env_obj` is on. This is true when invoking
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| 59 | `bin/ysh`.
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| 60 | 2. When running `bin/osh -o ysh:upgrade` or `ysh:all`.
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| 61 | 3. When running `shopt --set ysh:upgrade` or `ysh:all`.
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| 62 |
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| 63 | Related: [ysh-shopt][], [osh-usage][]
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| 64 |
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| 65 | [ysh-shopt]: chap-builtin-cmd.html#ysh-shopt
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| 66 | [osh-usage]: chap-front-end.html#osh-usage
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| 67 |
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| 68 | ---
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| 69 |
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| 70 | When launching an external command, the shell creates a Unix `environ` from the
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| 71 | `ENV` Obj. This means that mutating it affects all subsequent processes:
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| 72 |
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| 73 | setglobal ENV.PYTHONPATH = '.'
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| 74 | ./foo.py
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| 75 | ./bar.py
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| 76 |
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| 77 | You can also limit the change to a single process, without `ENV`:
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| 78 |
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| 79 | PYTHONPATH=. ./foo.py
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| 80 | ./bar.py # unaffected
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| 81 |
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| 82 | ---
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| 83 |
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| 84 | YSH reads these ENV variables:
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| 85 |
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| 86 | - `PATH` - where to look for executables
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| 87 | - `PS1` - how to print the prompt
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| 88 | - TODO: `PS4` - how to show execution traces
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| 89 | - `YSH_HISTFILE` (`HISTFILE` in OSH) - where to read/write command history
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| 90 | - `HOME` - for tilde substitution ([tilde-sub])
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| 91 |
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| 92 | [tilde-sub]: chap-word-lang.html#tilde-sub
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| 93 |
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| 94 | ### `__defaults__`
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| 95 |
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| 96 | The shell puts some default settings in this `Dict`. In certain situations, it
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| 97 | consults `__defaults__` after consulting `ENV`. For example:
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| 98 |
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| 99 | - if `ENV.PATH` is not set, consult `__defaults__.PATH`
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| 100 | - if `ENV.PS1` is not set, consult `__defaults__.PS1`
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| 101 |
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| 102 | <!-- TODO: consider renaming to DEF.PS1 ? -->
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| 103 |
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| 104 | ### `__builtins__`
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| 105 |
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| 106 | An object that contains names visible in every module.
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| 107 |
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| 108 | If a name is not visible in the local scope, or module global scope, then it's
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| 109 | looked up in `__builtins__`.
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| 110 |
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| 111 | ### `__sh_function__`
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| 112 |
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| 113 | A Dict that reflects the shell functions defined in the Oils interpreter.
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| 114 |
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| 115 | = keys(__sh_function__) # enumerate all shell functions
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| 116 |
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| 117 | = get(__sh_function__, 'f') # get a value of type Proc
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| 118 |
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| 119 | = __sh_function__ => get('f') # synonym for the above
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| 120 |
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| 121 | You can reflect on [doc comments][doc-comment] by calling the [docComment][]
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| 122 | method on a value of type [Proc][].
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| 123 |
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| 124 | [doc-comment]: chap-front-end.html#doc-comment
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| 125 | [docComment]: chap-type-method.html#docComment
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| 126 | [Proc]: chap-type-method.html#Proc
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| 127 |
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| 128 | ### `_this_dir`
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| 129 |
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| 130 | The directory the current script resides in. This knows about 3 situations:
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| 131 |
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| 132 | - The location of `oshrc` in an interactive shell
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| 133 | - The location of the main script, e.g. in `osh myscript.sh`
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| 134 | - The location of script loaded with the `source` builtin
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| 135 |
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| 136 | It's useful for "relative imports".
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| 137 |
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| 138 | ## YSH Status
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| 139 |
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| 140 | ### `_status`
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| 141 |
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| 142 | DEPRECATED: Use `_error.code` instead.
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| 143 |
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| 144 | ### `_error`
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| 145 |
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| 146 | A `Dict` that's set by the `try` builtin.
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| 147 |
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| 148 | The integer `_error.code` is always present:
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| 149 |
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| 150 | try {
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| 151 | ls /tmp
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| 152 | }
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| 153 | echo "status is $[_error.code]"
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| 154 |
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| 155 | Some errors also have a `message` field, like JSON/J8 encoding/decoding errors,
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| 156 | and user errors from the [error][] builtin.
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| 157 |
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| 158 | try {
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| 159 | echo $[toJson( /d+/ )] # invalid Eggex type
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| 160 | }
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| 161 | echo "failed: $[_error.message]" # => failed: Can't serialize ...
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| 162 |
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| 163 | [error]: chap-builtin-cmd.html#error
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| 164 |
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| 165 |
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| 166 | ### `_pipeline_status`
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| 167 |
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| 168 | After a pipeline of processes is executed, this array contains the exit code of
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| 169 | each process.
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| 170 |
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| 171 | Each exit code is an [Int](chap-type-method.html#Int). Compare with
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| 172 | [`PIPESTATUS`](#PIPESTATUS).
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| 173 |
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| 174 | ### `_process_sub_status`
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| 175 |
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| 176 | The exit status of all the process subs in the last command.
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| 177 |
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| 178 | ## YSH Tracing
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| 179 |
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| 180 | ### SHX_indent
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| 181 |
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| 182 | ### SHX_punct
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| 183 |
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| 184 | ### SHX_pid_str
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| 185 |
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| 186 | ## YSH Read
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| 187 |
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| 188 | ### _reply
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| 189 |
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| 190 | Builtins that `read` set this variable:
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| 191 |
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| 192 | read --all < foo.txt
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| 193 | = _reply # => 'contents of file'
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| 194 |
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| 195 | json read < foo.json
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| 196 | = _reply # => (Dict) {}
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| 197 |
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| 198 | ## Oils VM
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| 199 |
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| 200 | ### `OILS_VERSION`
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| 201 |
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| 202 | The version of Oils that's being run, e.g. `0.23.0`.
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| 203 |
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| 204 | <!-- TODO: specify comparison algorithm. -->
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| 205 |
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| 206 | ### `LIB_OSH`
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| 207 |
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| 208 | The string `///osh`, which you can use with the [source][] builtin.
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| 209 |
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| 210 | source $LIB_OSH/two.sh
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| 211 |
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| 212 | [source]: chap-builtin-cmd.html#source
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| 213 |
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| 214 | ### `LIB_YSH`
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| 215 |
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| 216 | The string `///ysh`, which you can use with the [source][] builtin.
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| 217 |
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| 218 | source $LIB_YSH/yblocks.ysh
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| 219 |
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| 220 | [source]: chap-builtin-cmd.html#source
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| 221 |
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| 222 | ### `OILS_GC_THRESHOLD`
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| 223 |
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| 224 | At a GC point, if there are more than this number of live objects, collect
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| 225 | garbage.
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| 226 |
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| 227 | ### `OILS_GC_ON_EXIT`
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| 228 |
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| 229 | Set `OILS_GC_ON_EXIT=1` to explicitly collect and `free()` before the process
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| 230 | exits. By default, we let the OS clean up.
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| 231 |
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| 232 | Useful for ASAN testing.
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| 233 |
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| 234 | ### `OILS_GC_STATS`
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| 235 |
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| 236 | When the shell process exists, print GC stats to stderr.
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| 237 |
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| 238 | ### `OILS_GC_STATS_FD`
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| 239 |
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| 240 | When the shell process exists, print GC stats to this file descriptor.
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| 241 |
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| 242 | ### `OILS_LOCALE_OK`
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| 243 |
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| 244 | Suppress the warning about `libc` locales that are not UTF-8.
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| 245 |
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| 246 | ## libc locale
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| 247 |
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| 248 | ### osh-locale
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| 249 |
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| 250 | At startup, reads these env vars and sets global vars in `libc`:
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| 251 |
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| 252 | - `LC_CTYPE`
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| 253 | - Affects how certain `libc` string functions handle bytes versus code
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| 254 | points. For example, what do `?` in globs and `.` in regexes mean?
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| 255 | - `LC_COLLATE`
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| 256 | - Affects [glob][osh-glob] sort order.
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| 257 |
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| 258 | This is done with libc's `setlocale()` function.
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| 259 |
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| 260 | [osh-glob]: chap-word-lang.html#osh-glob
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| 261 |
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| 262 | ### ysh-locale
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| 263 |
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| 264 | At startup, reads these env vars and sets global vars in `libc`:
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| 265 |
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| 266 | - `LC_CTYPE`
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| 267 |
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| 268 | This is done with libc's `setlocale()` function.
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| 269 |
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| 270 | [ysh-glob]: chap-word-lang.html#ysh-glob
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| 271 |
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| 272 | ## Interactive
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| 273 |
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| 274 | ### OILS_COMP_UI
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| 275 |
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| 276 | Set which completion UI to use. Defaults to `minimal`.
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| 277 |
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| 278 | - `minimal` - a UI that approximates the default behavior of GNU readline.
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| 279 | - `nice` - a UI with a fancy pager and a prompt with horizontal scrolling instead of wrapping.
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| 280 |
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| 281 | This variable is currently only checked once during shell initialization.
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| 282 |
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| 283 | ### HISTFILE
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| 284 |
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| 285 | Override the default OSH history location.
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| 286 |
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| 287 | ### YSH_HISTFILE
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| 288 |
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| 289 | Override the default YSH history location.
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| 290 |
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| 291 | ## Float
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| 292 |
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| 293 | ### NAN
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| 294 |
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| 295 | The float value for "not a number".
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| 296 |
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| 297 | (The name is consistent with the C language.)
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| 298 |
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| 299 | ### INFINITY
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| 300 |
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| 301 | The float value for "infinity". You can negate it to get "negative infinity".
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| 302 |
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| 303 | (The name is consistent with the C language.)
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| 304 |
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| 305 | ## Module
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| 306 |
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| 307 | ### `__provide__`
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| 308 |
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| 309 | A module is evaluated upon `use`. After evaluation, the names in the
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| 310 | `__provide__` `List` are put in the resulting module `Obj` instance.
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| 311 |
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| 312 | <!--
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| 313 | `__provide__` may also be a string, where 'p' stands for --procs, and 'f' stands for funcs.
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| 314 |
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| 315 | Or we could make it [1, 2] insetad
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| 316 | -->
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| 317 |
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| 318 | ## POSIX Special
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| 319 |
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| 320 | $@ $* all arguments
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| 321 | $0 ... $9 ${10} each argument
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| 322 | $# the number of arguments
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| 323 | $? last exit status
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| 324 | $-
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| 325 | $$ PID of shell (does not change when shell forks)
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| 326 | $! ID of last job started, with & or bg
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| 327 |
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| 328 | Details on `$!`:
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| 329 |
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| 330 | - It's either
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| 331 | - the PID of a process
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| 332 | - the PID of the *last* part of the pipeline. (In contrast, the PGID of the
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| 333 | pipeline is the PID of the first part.)
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| 334 | - The [`wait`](chap-builtin-cmd.html#wait) builtin knows how to find a
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| 335 | background pipeline job, given this ID.
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| 336 | - It's set by:
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| 337 | - [`ampersand &`](chap-cmd-lang.html#ampersand)
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| 338 | - [`bg`](chap-builtin-cmd.html#bg)
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| 339 | - In particular, it's not set after Ctrl-Z, only after `bg`.
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| 340 |
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| 341 | ## Shell Vars
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| 342 |
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| 343 | ### IFS
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| 344 |
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| 345 | Used for word splitting. And the builtin `shSplit()` function.
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| 346 |
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| 347 | ### LANG
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| 348 |
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| 349 | TODO: bash compat
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| 350 |
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| 351 | ### GLOBIGNORE
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| 352 |
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| 353 | TODO: bash compat
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| 354 |
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| 355 | ## Shell Options
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| 356 |
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| 357 | ### SHELLOPTS
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| 358 |
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| 359 | bash compat: serialized options for the `set` builtin.
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| 360 |
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| 361 | ### BASHOPTS
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| 362 |
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| 363 | bash compat: serialized options for the `shopt` builtin.
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| 364 |
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| 365 | (Not implemented.)
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| 366 |
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| 367 | ## Other Env
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| 368 |
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| 369 | ### HOME
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| 370 |
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| 371 | The `$HOME` env var is read by the shell, for:
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| 372 |
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| 373 | 1. `~` expansion
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| 374 | 2. `~` abbreviation in the UI (the dirs builtin, `\W` in `$PS1`).
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| 375 |
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| 376 | The shell does not set $HOME. According to POSIX, the program that invokes the
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| 377 | login shell should set it, based on `/etc/passwd`.
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| 378 |
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| 379 | ### PATH
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| 380 |
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| 381 | A colon-separated string that's used to find executables to run.
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| 382 |
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| 383 | In YSH, it's `ENV.PATH`.
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| 384 |
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| 385 | ## Other Special
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| 386 |
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| 387 | ### BASH_REMATCH
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| 388 |
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| 389 | Result of regex evaluation `[[ $x =~ $pat ]]`.
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| 390 |
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| 391 | ### PIPESTATUS
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| 392 |
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| 393 | After a pipeline of processes is executed, this array contains the exit code of
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| 394 | each process.
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| 395 |
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| 396 | Each exit code is a [Str](chap-type-method.html#Str). Compare with
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| 397 | [`_pipeline_status`](#_pipeline_status).
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| 398 |
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| 399 | ## Platform
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| 400 |
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| 401 | ### HOSTNAME
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| 402 |
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| 403 | The name of the "host" or machine that Oils is running on, determined by
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| 404 | `gethostname()`.
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| 405 |
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| 406 | ### OSTYPE
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| 407 |
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| 408 | The operating system that Oils is running on, determined by `uname()`.
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| 409 |
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| 410 | Examples: `linux darwin ...`
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| 411 |
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| 412 | ## Call Stack
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| 413 |
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| 414 | ### BASH_SOURCE
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| 415 |
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| 416 | ### FUNCNAME
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| 417 |
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| 418 | ### BASH_LINENO
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| 419 |
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| 420 | ## Tracing
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| 421 |
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| 422 | ### LINENO
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| 423 |
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| 424 | ## Process State
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| 425 |
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| 426 | ### BASHPID
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| 427 |
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| 428 | TODO
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| 429 |
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| 430 | ### PPID
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| 431 |
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| 432 | TODO
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| 433 |
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| 434 | ### UID
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| 435 |
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| 436 | ### EUID
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| 437 |
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| 438 | ## Process Stack
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| 439 |
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| 440 | ## Shell State
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| 441 |
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| 442 | ## Completion
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| 443 |
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| 444 | ### COMP_WORDS
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| 445 |
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| 446 | An array of words, split by : and = for compatibility with bash. New
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| 447 | completion scripts should use COMP_ARGV instead.
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| 448 |
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| 449 | ### COMP_CWORD
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| 450 |
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| 451 | Discouraged; for compatibility with bash.
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| 452 |
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| 453 | ### COMP_LINE
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| 454 |
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| 455 | Discouraged; for compatibility with bash.
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| 456 |
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| 457 | ### COMP_POINT
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| 458 |
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| 459 | Discouraged; for compatibility with bash.
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| 460 |
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| 461 | ### COMP_WORDBREAKS
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| 462 |
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| 463 | Discouraged; for compatibility with bash.
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| 464 |
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| 465 | ### COMPREPLY
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| 466 |
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| 467 | User-defined completion functions should Fill this array with candidates. It
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| 468 | is cleared on every completion request.
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| 469 |
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| 470 | ### COMP_ARGV
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| 471 |
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| 472 | An array of partial command arguments to complete. Preferred over COMP_WORDS.
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| 473 | The compadjust builtin uses this variable.
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| 474 |
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| 475 | (An OSH extension to bash.)
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| 476 |
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| 477 | ## cd
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| 478 |
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| 479 | ### PWD
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| 480 |
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| 481 | ### OLDPWD
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| 482 |
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| 483 | ### CDPATH
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| 484 |
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| 485 | ## getopts
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| 486 |
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| 487 | ### OPTIND
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| 488 |
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| 489 | ### OPTARG
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| 490 |
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| 491 | ### OPTERR
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| 492 |
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| 493 | ## read
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| 494 |
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| 495 | ### REPLY
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| 496 |
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| 497 | OSH read sets this:
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| 498 |
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| 499 | read < myfile
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| 500 |
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| 501 | ## Functions
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| 502 |
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| 503 | ### RANDOM
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| 504 |
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| 505 | bash compat
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| 506 |
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| 507 | ### SECONDS
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| 508 |
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| 509 | bash compat
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| 510 |
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