| 1 | ---
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| 2 | title: Global Shell Options (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 **Global Shell Options**
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| 13 |
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| 14 | </div>
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| 15 |
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| 16 | This chapter describes global shell options in Oils. Some options are from
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| 17 | POSIX shell, and some are from [bash]($xref). We also use options to turn
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| 18 | [OSH]($xref) into [YSH]($xref).
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| 19 |
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| 20 | <span class="in-progress">(in progress)</span>
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| 21 |
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| 22 | <div id="dense-toc">
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| 23 | </div>
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| 24 |
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| 25 | ## Errors
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| 26 |
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| 27 | These options are from POSIX shell:
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| 28 |
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| 29 | nounset -u
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| 30 | errexit -e
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| 31 | pipefail
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| 32 |
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| 33 | These are from bash:
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| 34 |
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| 35 | inherit_errexit
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| 36 |
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| 37 | ## Globbing
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| 38 |
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| 39 | These options are from POSIX shell:
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| 40 |
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| 41 | noglob -f # don't perform globbing
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| 42 |
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| 43 | From bash:
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| 44 |
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| 45 | nullglob # if the glob matches nothing, it expands to no args
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| 46 | failglob # if the glob matches nothing, it's a fatal error
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| 47 | dotglob # include files starting with . like .gitignore
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| 48 | globskipdots # by default, omit . and .. (even if pattern starts with .)
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| 49 |
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| 50 | From Oils:
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| 51 |
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| 52 | no_dash_glob
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| 53 |
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| 54 | Some details:
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| 55 |
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| 56 | ### dotglob
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| 57 |
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| 58 | Does glob expansion return files that start with a period?
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| 59 |
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| 60 | # By default, we don't return say .gitignore
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| 61 | $ echo * # foo
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| 62 |
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| 63 | $ shopt -s dotglob # set this option
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| 64 | $ echo * # => .gitignore foo
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| 65 |
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| 66 | This option is on by default in OSH and YSH.
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| 67 |
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| 68 | ### nullglob
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| 69 |
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| 70 | When `nullglob` is on, a glob matching no files expands to no arguments:
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| 71 |
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| 72 | shopt -s nullglob
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| 73 | $ echo L *.py R
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| 74 | L R
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| 75 |
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| 76 | Without this option, the glob string itself is returned:
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| 77 |
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| 78 | $ echo L *.py R # no Python files in this dir
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| 79 | L *.py R
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| 80 |
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| 81 | (This option is from GNU bash.)
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| 82 |
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| 83 | YSH doesn't use this option, but its [Simple Word
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| 84 | Evaluation](../simple-word-eval.html) algorithm behaves similarly.
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| 85 |
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| 86 | ### no_dash_glob
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| 87 |
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| 88 | Do globs return results that start with `-`? It's on by default in `bin/osh`,
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| 89 | but off when YSH is enabled.
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| 90 |
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| 91 | Turning it off prevents a command like `rm *` from being confused by a file
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| 92 | called `-rf`.
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| 93 |
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| 94 | $ touch -- myfile -rf
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| 95 |
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| 96 | $ echo *
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| 97 | -rf myfile
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| 98 |
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| 99 | $ shopt -s no_dash_glob
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| 100 | $ echo *
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| 101 | myfile
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| 102 |
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| 103 | This option is off in OSH, and on in YSH.
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| 104 |
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| 105 | ## Other Option
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| 106 |
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| 107 | noclobber -C # Redirects can't overwrite files
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| 108 |
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| 109 | ## Debugging
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| 110 |
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| 111 | <h3 id="errtrace">errtrace (-E)</h3>
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| 112 |
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| 113 | Enable the ERR [trap][] in both shell functions and subshells.
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| 114 |
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| 115 | The option is also `set -E`. It's designed to be compatible with bash.
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| 116 |
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| 117 | [trap]: chap-builtin-cmd.html#trap
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| 118 |
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| 119 | ### extdebug
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| 120 |
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| 121 | Show more info in when printing functions with `declare -f`. Used by
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| 122 | `task-five.sh`.
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| 123 |
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| 124 | <h3 id="xtrace">xtrace (-x)</h3>
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| 125 |
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| 126 | Show execution traces.
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| 127 |
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| 128 | - In OSH, the [PS4][] variables control the display.
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| 129 | - In YSH, the `SHX_*` variables control the display.
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| 130 |
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| 131 | [PS4]: chap-plugin.html#PS4
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| 132 |
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| 133 | This option is also `set -x`. It's required by POSIX shell.
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| 134 |
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| 135 | ### verbose
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| 136 |
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| 137 | Not implemented.
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| 138 |
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| 139 | This option is from POSIX shell.
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| 140 |
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| 141 | ## Interactive
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| 142 |
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| 143 | These options are from bash.
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| 144 |
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| 145 | emacs vi
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| 146 |
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| 147 |
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| 148 | ## Compat
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| 149 |
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| 150 | ### eval_unsafe_arith
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| 151 |
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| 152 | Allow dynamically parsed `a[$(echo 42)]` For bash compatibility.
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| 153 |
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| 154 | ### ignore_flags_not_impl
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| 155 |
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| 156 | Suppress failures from unimplemented flags. Example:
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| 157 |
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| 158 | shopt --set ignore_flags_not_impl
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| 159 |
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| 160 | declare -i foo=2+3 # not evaluated to 5, but doesn't fail either
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| 161 |
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| 162 | This option can be useful for "getting past" errors while testing.
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| 163 |
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| 164 | ### ignore_shopt_not_impl
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| 165 |
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| 166 | Suppress failures from unimplemented shell options. Example:
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| 167 |
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| 168 | shopt --set ignore_shopt_not_impl
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| 169 |
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| 170 | shopt --set xpg_echo # exit with status 0, not 1
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| 171 | # this is a bash option that OSH doesn't implement
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| 172 |
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| 173 | This option can be useful for "getting past" errors while testing.
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| 174 |
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| 175 | ## Optimize
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| 176 |
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| 177 | ### rewrite_extern
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| 178 |
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| 179 | This option enables a transparent rewriting of external commands to
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| 180 | **builtins**.
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| 181 |
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| 182 | Currently, these commands **may** be rewritten, depending on their `argv`:
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| 183 |
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| 184 | - [cat][]
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| 185 | - [rm][]
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| 186 |
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| 187 | These optimizations are *sound* - they should not affect the behavior of
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| 188 | programs on a POSIX system.
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| 189 |
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| 190 | ---
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| 191 |
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| 192 | This option is on by default in OSH and YSH, but it applies only in
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| 193 | non-interactive shells. That is, in interactive shells, commands are **never**
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| 194 | rewritten, regardless of the value of `rewrite_extern`.
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| 195 |
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| 196 | [cat]: chap-builtin-cmd.html#cat
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| 197 | [rm]: chap-builtin-cmd.html#rm
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| 198 |
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| 199 | ### ysh_rewrite_extern
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| 200 |
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| 201 | This option transparently avoids compatibility workarounds when rewriting
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| 202 | external commands to **builtins**, providing a performance improvement.
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| 203 | It might affect the behavior of programs on a POSIX system.
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| 204 |
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| 205 | Currently, this only affects [cat][], which otherwise runs in a separate
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| 206 | process (so that its errors do not crash the main process).
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| 207 |
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| 208 | [cat]: chap-builtin-cmd.html#cat
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| 209 |
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| 210 | ## Groups
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| 211 |
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| 212 | To turn OSH into YSH, we use three option groups. Some of them allow new
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| 213 | features, and some disallow old features.
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| 214 |
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| 215 | <!-- note: explicit anchor necessary because of mangling -->
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| 216 | <h3 id="strict:all">strict:all</h3>
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| 217 |
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| 218 | Option in this group disallow problematic or confusing shell constructs. The
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| 219 | resulting script will still run in another shell.
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| 220 |
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| 221 | shopt --set strict:all # turn on all options
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| 222 | shopt -p strict:all # print their current state
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| 223 |
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| 224 | Parsing options:
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| 225 |
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| 226 | strict_parse_equals # Disallow '=x' to avoid confusion with '= x'
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| 227 | strict_parse_slice # No implicit length for ${a[@]::}
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| 228 | X strict_parse_utf8 # Source code must be valid UTF-8
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| 229 |
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| 230 | Runtime options:
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| 231 |
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| 232 | strict_arg_parse # Disallow additional arguments to some builtins
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| 233 | strict_argv # No empty argv
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| 234 | strict_arith # Fatal parse errors (on by default)
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| 235 | strict_array # Arrays and strings aren't confused
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| 236 | strict_control_flow # Disallow misplaced keyword, empty arg
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| 237 | strict_env_binding # Prefix bindings must always be env bindings
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| 238 | strict_errexit # Disallow code that ignores failure
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| 239 | strict_nameref # Trap invalid variable names
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| 240 | strict_word_eval # Expose unicode and slicing errors
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| 241 | strict_tilde # Tilde subst can result in error
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| 242 | X strict_glob # Parse the sublanguage more strictly
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| 243 |
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| 244 | <h3 id="ysh:upgrade">ysh:upgrade</h3>
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| 245 |
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| 246 | Options in this group enable new YSH features. It doesn't break existing shell
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| 247 | scripts when it's avoidable.
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| 248 |
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| 249 | For example, `parse_at` means that `@myarray` is now the operation to splice
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| 250 | an array. This will break scripts that expect `@` to be literal, but you can
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| 251 | simply quote it like `'@literal'` to fix the problem.
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| 252 |
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| 253 | shopt --set ysh:upgrade # turn on all options
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| 254 | shopt -p ysh:upgrade # print their current state
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| 255 |
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| 256 | Details on each option:
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| 257 |
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| 258 | parse_at echo @array @[arrayfunc(x, y)]
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| 259 | parse_brace if true { ... }; cd ~/src { ... }
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| 260 | parse_equals x = 'val' in Caps { } config blocks
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| 261 | parse_paren if (x > 0) ...
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| 262 | parse_proc proc p { ... }
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| 263 | parse_triple_quote """$x""" '''x''' (command mode)
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| 264 | parse_ysh_string echo r'\' u'\\' b'\\' (command mode)
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| 265 | parse_ysh_expr_sub $[] is YSH expression sub, not synonym for $(( ))
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| 266 | command_sub_errexit Synchronous errexit check
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| 267 | process_sub_fail Analogous to pipefail for process subs
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| 268 | sigpipe_status_ok status 141 -> 0 in pipelines
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| 269 | simple_word_eval No splitting, static globbing
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| 270 | xtrace_rich Hierarchical and process tracing
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| 271 | no_xtrace_osh Disable OSH tracing with +
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| 272 | no_dash_glob Avoid globbing files like -rf
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| 273 | env_obj Init ENV Obj at startup; use it when starting
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| 274 | child processes
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| 275 | init_ysh_globals Init ARGV List at startup
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| 276 | for_loop_frames YSH can create closures from loop vars
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| 277 | verbose_errexit Whether to print detailed errors
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| 278 | verbose_warn Print various warnings to stderr
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| 279 | ysh_rewrite_extern Avoids compatibility workarounds for builtins
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| 280 |
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| 281 | <h3 id="ysh:all">ysh:all</h3>
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| 282 |
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| 283 | Enable the full YSH language. This includes everything in the `ysh:upgrade`
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| 284 | group and the `strict:all` group.
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| 285 |
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| 286 | shopt --set ysh:all # turn on all options
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| 287 | shopt -p ysh:all # print their current state
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| 288 |
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| 289 | Details on options that are not in `ysh:upgrade` and `strict:all`:
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| 290 |
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| 291 | expand_aliases (-u) Whether aliases are expanded
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| 292 | parse_at_all @ starting any word is an operator
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| 293 | no_parse_backslash Disallow bad backslashes in "" and $''
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| 294 | no_parse_backticks Disallow `echo hi`
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| 295 | no_parse_bare_word Disallow 'case unquoted' 'for x in unquoted'
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| 296 | no_parse_dbracket Disallow legacy booleans [[
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| 297 | no_parse_dollar Disallow bare $ for \$ (maybe $/d+/)
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| 298 | no_parse_dparen Disallow legacy arithmetic ((
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| 299 | no_parse_ignored Don't parse redirects that are ignored
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| 300 | no_parse_osh No $'' ( ) & TODO ${x%prefix} ${a[@]} $$
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| 301 | no_parse_sh_arith Disallow legacy shell arithmetic
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| 302 | no_parse_word_join Disallow pitfall --flag=r'value'
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| 303 | no_exported Environ doesn't correspond to exported (-x) vars
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| 304 | no_init_globals At startup, don't set vars like PWD, SHELLOPTS
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| 305 | no_osh_builtins Disallow OSH builtins like alias, unalias, etc.
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| 306 | simple_echo echo doesn't accept -e -n
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| 307 | simple_eval_builtin eval takes exactly 1 argument
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| 308 | simple_test_builtin test takes 2 or 3 args; use test not [
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| 309 | simple_trap_builtin trap doesn't take a code string, etc.
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| 310 | X simple_trap Function name only
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| 311 |
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| 312 | **Caveat**: Some options only affect shell startup. For example:
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| 313 |
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| 314 | - If you start with `osh`, and the script runs `shopt --set ysh:all`, then the
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| 315 | YSH [ARGV][] var won't be initialized.
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| 316 | - In contrast, if you run `osh -o ysh:all -c 'echo @ARGV'`, then [ARGV][] will
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| 317 | be initialized. That is, shell startup is done "the YSH way".
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| 318 |
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| 319 | [ARGV]: chap-special-var.html#ARGV
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| 320 |
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| 321 | ## YSH Details
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| 322 |
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| 323 | ### opts-redefine
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| 324 |
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| 325 | In the interactive shell, you can redefine procs and funcs.
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| 326 |
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| 327 | redefine_source 'source-guard' builtin always returns 0
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| 328 | X redefine_const Can consts be redefined?
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| 329 |
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| 330 | ### opts-internal
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| 331 |
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| 332 | These options are used by the interpreter. You generally shouldn't set them
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| 333 | yourself.
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| 334 |
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| 335 | _allow_command_sub To implement strict_errexit, eval_unsafe_arith
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| 336 | _allow_process_sub To implement strict_errexit
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| 337 | dynamic_scope To implement proc and func
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| 338 | _no_debug_trap Used in pipelines in job control shell
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| 339 | _running_trap To disable strict_errexit
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| 340 | _running_hay Hay evaluation
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| 341 |
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| 342 | ## Unlinked Descriptions
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| 343 |
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| 344 | Here are some descriptions of individual options.
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| 345 |
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| 346 | ### strict_control_flow
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| 347 |
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| 348 | Disallow `break` and `continue` at the top level, and disallow empty args like
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| 349 | `return $empty`.
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| 350 |
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| 351 | ### strict_tilde
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| 352 |
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| 353 | Failed tilde expansions cause hard errors (like zsh) rather than silently
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| 354 | evaluating to `~` or `~bad`.
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| 355 |
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| 356 |
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| 357 | ### strict_nameref
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| 358 |
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| 359 | When `strict_nameref` is set, undefined references produce fatal errors:
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| 360 |
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| 361 | declare -n ref
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| 362 | echo $ref # fatal error, not empty string
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| 363 | ref=x # fatal error instead of decaying to non-reference
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| 364 |
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| 365 | References that don't contain variables also produce hard errors:
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| 366 |
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| 367 | declare -n ref='not a var'
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| 368 | echo $ref # fatal
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| 369 | ref=x # fatal
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| 370 |
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| 371 | ### no_parse_ignored
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| 372 |
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| 373 | For compatibility, OSH will parse some constructs it doesn't execute, like:
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| 374 |
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| 375 | return 0 2>&1 # redirect on control flow
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| 376 |
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| 377 | When this option is disabled, that statement is a syntax error.
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| 378 |
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| 379 | ### parse_triple_quote
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| 380 |
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| 381 | Parse the shell-style multi-line strings, which strip leading whitespace:
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| 382 |
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| 383 | echo '''
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| 384 | one
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| 385 | two
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| 386 | '''
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| 387 |
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| 388 | echo """
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| 389 | hello
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| 390 | $name
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| 391 | """
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| 392 |
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| 393 | (This option affects only command mode. Such strings are always parsed in
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| 394 | expression mode.)
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| 395 |
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| 396 | ### parse_ysh_string
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| 397 |
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| 398 | Allow `r'\'` and `u'\\'` and `b'\\'` strings, as well as their multi-line
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| 399 | versions.
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| 400 |
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| 401 | Since shell strings are already raw, this means that YSH just ignores the r
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| 402 | prefix:
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| 403 |
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| 404 | echo r'\' # a single backslash
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| 405 |
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| 406 | J8 unicode strings:
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| 407 |
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| 408 | echo u'mu \u{3bc}' # mu char
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| 409 |
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| 410 | J8 byte strings:
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| 411 |
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| 412 | echo b'byte \yff'
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| 413 |
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| 414 | (This option affects only command mode. Such strings are always parsed in
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| 415 | expression mode.)
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| 416 |
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| 417 | ### sigpipe_status_ok
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| 418 |
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| 419 | If a process that's part of a pipeline exits with status 141 when this is
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| 420 | option is on, it's turned into status 0, which avoids failure.
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| 421 |
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| 422 | SIGPIPE errors occur in cases like 'yes | head', and generally aren't useful.
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| 423 |
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