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