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1 *usr_46.txt* For Vim version 8.2. Last change: 2020 Jun 14
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3 VIM USER MANUAL - by Bram Moolenaar
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4
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5 Write plugins using Vim9 script
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6
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7
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8 The Vim9 script language is used for writing plugins, especially larger ones
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9 that use multiple files. This chapter explains how to split up a plugin into
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10 modules, import and export items and keep the rest local.
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11
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12 |46.1| Introduction
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13 |46.2| Variable declarations
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14 |46.3| Functions and types
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15 |46.?| Using a Vim9 script from legacy script
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16
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17 Next chapter: |usr_90.txt| Installing Vim
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18 Previous chapter: |usr_45.txt| Select your language (locale)
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19 Table of contents: |usr_toc.txt|
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20
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21 ==============================================================================
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22 *46.1* Introduction *vim9-script-intro*
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23
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24 Vim9 script was designed to make it easier to write large Vim scripts. It
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25 looks more like other script languages, especially Typescript. Also,
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26 functions are compiled into instructions that can be executed quickly. This
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27 makes Vim9 script a lot faster, up to a 100 times.
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28
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29 The basic idea is that a script file has items that are private, only used
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30 inside the script file, and items that are exported, used outside of the
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31 script file. The exported items can then be used by scripts that import them.
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32 That makes very clear what is defined where.
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33
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34 Let's start with an example, a script that exports one function and has one
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35 private function: >
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36
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37 vim9script " This indicates a Vim9 script file.
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38
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39 export def GetMessage(): string
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40 let result = ''
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41 ...
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42 result = GetPart(count)
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43 ...
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44 return result
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45 enddef
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46
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47 def GetPart(nr: number): string
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48 if nr == 4
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49 return 'yes'
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50 else
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51 return 'no'
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52 endif
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53 enddef
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54
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55 The `vim9script` command must be the very first command in the file. Without
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56 it Vim will assume legacy script syntax.
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57
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58 The `export def GetMessage(): string` line starts with `export`, meaning that
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59 this function can be imported and called by other scripts. The line
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60 `def GetPart(...` does not start with `export`, this is a script-local
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61 function, it can only be used inside this script file.
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62
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63 In the `export def GetMessage(): string` line you will notice the colon and
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64 the return type. Vim9 functions, defined with `def`, require specifying the
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65 type of arguments and the return type. That way Vim can compile the code
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66 efficiently. The GetPart function defines an argument "nr" of type "number".
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67
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68 Notice that the assignment `result = GetPart(count)` does not use the `let`
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69 command. That is explained in the next section.
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70
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71 ==============================================================================
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72 *46.2* Variable declarations *vim9-declarations*
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73
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74 In Vim9 script variables are declared once with a `:let` or `:const` command.
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75 Assigning a value is done without `:let` and it is not possible to `:unlet`
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76 the variable.
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77
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78 In most cases you will want to declare the variable and initialize it at the
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79 same time: >
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80 let myText = 'some text'
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81 ...
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82 myText = 'other text'
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83
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84 The type of the variable will be inferred from the expression. In this case
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85 it is a string. If you initialize with a number, then the type is number: >
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86 let myNumber = 1234
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87 ...
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88 myNumber = 0
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89
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90 If you try to assign a string to this variable, you will get an error: >
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91 let myNumber = 'this fails!'
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92
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93 In the rare case you want a variable that can take values of any type, you
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94 have to specify the type: >
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95 let myVar: any = 1234
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96 myVar = 'text also works'
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97
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98 You can also declare a variable without assigning a value. In that case Vim
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99 will initialize it to zero or empty: >
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100 let word: string
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101 if condition
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102 word = 'yes'
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103 else
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104 word = 'no'
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105 endif
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106
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107 Although it's shorter to do: >
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108 let word = condition ? 'yes' : 'no'
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109
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110 ==============================================================================
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111 *46.3* Functions and types
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112
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113 Legacy Vim script does have type checking, but this happens at runtime, when
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114 the code is executed. And it's permissive, often a computation gives an
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115 unexpected value instead of reporting an error. Thus you can define a
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116 function and think it's fine, but see a problem only later when it is called: >
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117 let s:collected = ''
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118 func ExtendAndReturn(add)
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119 let s:collected += a:add
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120 return s:collected
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121 endfunc
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122
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123 Can you spot the error? Try this: >
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124 echo ExtendAndReturn('text')
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125 And you'll see zero. Why? Because in legacy Vim script "+=" will convert the
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126 arguments to numbers, and any string without a number results in zero!
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127
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128 With `:def` the type checking happens when compiling the function. For that
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129 you need to specify the argument types and the return type. Also notice that
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130 the argument is used without the "a:" prefix: >
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131 let s:collected = ''
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132 def ExtendAndReturn(add: string): string
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133 s:collected += add
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134 return s:collected
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135 enddef
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136 defcompile
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137
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138 Here we use `:defcompile` to do the compilation right away, without it the
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139 compilation would happen when the function is called. Vim will tell you what
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140 you did wrong: >
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141 E1013: type mismatch, expected number but got string
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142
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143 Vim9 script is strict, it uses the "+" operator only for numbers and floats.
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144 For string concatenation ".." must be used. This avoids mistakes and avoids
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145 the automatic conversion that gave a surprising result above. So you change
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146 the first line of the function to: >
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147 s:collected ..= add
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148 And now it works.
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149
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150 If the function does not return anything, just leave out the return type: >
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151 def ReportResult(result: string)
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152 echo 'The result is: ' .. result
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153 enddef
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154
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155 This is also checked, if you try to return a value you'll get an error.
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156
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157 In case you don't care about types or have a function that does work with
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158 multiple types, you can use the "any" type: >
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159 def Store(key: string, value: any)
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160 resultDict[key] = value
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161 enddef
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162
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163 ==============================================================================
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164 *46.?* Using a Vim9 script from legacy script *source-vim9-script*
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165
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166 In some cases you have a legacy Vim script where you want to use items from a
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167 Vim9 script. For example in your .vimrc you want to initialize a plugin. The
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168 best way to do this is to use `:import`. For example: >
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169
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170 import Init as NiceInit from 'myNicePlugin.vim'
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171 call NiceInit('today')
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172
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173 This finds the exported function "Init" in the Vim9 script file and makes it
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174 available as script-local item "NiceInit". `:import` always uses the script
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175 namespace, even when "s:" is not given. If "myNicePlugin.vim" was already
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176 sourced it is not sourced again.
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177
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178 Besides avoiding putting any items in the global namespace (where name clashes
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179 can cause unexpected errors), this also means the script is sourced only once,
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180 no matter how many times items from it are imported.
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181
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182 In some cases, e.g. for testing, you may just want to source the Vim9 script.
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183 That is OK, but then only global items will be available. The Vim9 script
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184 will have to make sure to use a unique name for these global items. Example: >
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185 source ~/.vim/extra/myNicePlugin.vim
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186 call g:NicePluginTest()
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187
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188 ==============================================================================
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189
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190 Next chapter: |usr_90.txt| Installing Vim
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191
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192 Copyright: see |manual-copyright| vim:tw=78:ts=8:noet:ft=help:norl:
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