1 | =head1 Name |
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2 | |
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3 | patching.pod - Appropriate format for patches to the perl source tree |
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4 | |
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5 | =head2 Where to get this document |
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6 | |
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7 | The latest version of this document is available from |
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8 | http://perrin.dimensional.com/perl/perlpatch.html |
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9 | |
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10 | =head2 How to contribute to this document |
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11 | |
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12 | You may mail corrections, additions, and suggestions to me |
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13 | at dgris@dimensional.com but the preferred method would be |
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14 | to follow the instructions set forth in this document and |
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15 | submit a patch 8-). |
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16 | |
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17 | =head1 Description |
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18 | |
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19 | =head2 Why this document exists |
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20 | |
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21 | As an open source project Perl relies on patches and contributions from |
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22 | its users to continue functioning properly and to root out the inevitable |
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23 | bugs. But, some users are unsure as to the I<right> way to prepare a patch |
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24 | and end up submitting seriously malformed patches. This makes it very |
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25 | difficult for the current maintainer to integrate said patches into their |
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26 | distribution. This document sets out usage guidelines for patches in an |
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27 | attempt to make everybody's life easier. |
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28 | |
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29 | =head2 Common problems |
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30 | |
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31 | The most common problems appear to be patches being mangled by certain |
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32 | mailers (I won't name names, but most of these seem to be originating on |
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33 | boxes running a certain popular commercial operating system). Other problems |
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34 | include patches not rooted in the appropriate place in the directory structure, |
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35 | and patches not produced using standard utilities (such as diff). |
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36 | |
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37 | =head1 Proper Patch Guidelines |
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38 | |
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39 | =head2 What to patch |
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40 | |
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41 | Generally speaking you should patch the latest development release |
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42 | of perl. The maintainers of the individual branches will see to it |
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43 | that patches are picked up and applied as appropriate. |
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44 | |
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45 | =head2 How to prepare your patch |
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46 | |
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47 | =over 4 |
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48 | |
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49 | =item Creating your patch |
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50 | |
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51 | First, back up the original files. This can't be stressed enough, |
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52 | back everything up _first_. |
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53 | |
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54 | Also, please create patches against a clean distribution of the perl source. |
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55 | This ensures that everyone else can apply your patch without clobbering their |
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56 | source tree. |
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57 | |
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58 | =item diff |
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59 | |
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60 | While individual tastes vary (and are not the point here) patches should |
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61 | be created using either C<-u> or C<-c> arguments to diff. These produce, |
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62 | respectively, unified diffs (where the changed line appears immediately next |
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63 | to the original) and context diffs (where several lines surrounding the changes |
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64 | are included). See the manpage for diff for more details. |
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65 | |
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66 | The preferred method for creating a unified diff suitable for feeding |
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67 | to the patch program is: |
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68 | |
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69 | diff -u old-file new-file > patch-file |
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70 | |
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71 | Note the order of files. See below for how to create a patch from |
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72 | two directory trees. |
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73 | |
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74 | If your patch is for wider consumption, it may be better to create it as |
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75 | a context diff as some machines have broken patch utilities that choke on |
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76 | unified diffs. A context diff is made using C<diff -c> rather than |
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77 | C<diff -u>. |
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78 | |
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79 | GNU diff has many desirable features not provided by most vendor-supplied |
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80 | diffs. Some examples using GNU diff: |
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81 | |
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82 | # generate a patch for a newly added file |
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83 | % diff -u /dev/null new/file |
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84 | |
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85 | # generate a patch to remove a file (patch > v2.4 will remove it cleanly) |
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86 | % diff -u old/goner /dev/null |
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87 | |
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88 | # get additions, deletions along with everything else, recursively |
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89 | % diff -ruN olddir newdir |
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90 | |
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91 | # ignore whitespace |
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92 | % diff -bu a/file b/file |
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93 | |
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94 | # show function name in every hunk (safer, more informative) |
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95 | % diff -u -F '^[_a-zA-Z0-9]+ *(' old/file new/file |
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96 | |
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97 | |
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98 | =item Directories |
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99 | |
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100 | IMPORTANT: Patches should be generated from the source root directory, not |
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101 | from the directory that the patched file resides in. This ensures that the |
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102 | maintainer patches the proper file. |
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103 | |
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104 | Many files in the distribution are derivative--avoid patching them. |
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105 | Patch the originals instead. Most utilities (like perldoc) are in |
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106 | this category, i.e. patch utils/perldoc.PL rather than utils/perldoc. |
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107 | Similarly, don't create patches for files under $src_root/ext from |
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108 | their copies found in $install_root/lib. If you are unsure about the |
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109 | proper location of a file that may have gotten copied while building |
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110 | the source distribution, consult the C<MANIFEST>. |
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111 | |
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112 | =item Filenames |
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113 | |
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114 | The most usual convention when submitting patches for a single file is to make |
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115 | your changes to a copy of the file with the same name as the original. Rename |
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116 | the original file in such a way that it is obvious what is being patched |
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117 | ($file.dist or $file.old seem to be popular). |
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118 | |
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119 | If you are submitting patches that affect multiple files then you should |
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120 | backup the entire directory tree (to $source_root.old/ for example). This |
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121 | will allow C<diff -ruN old-dir new-dir> to create all the patches at once. |
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122 | |
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123 | =item Try it yourself |
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124 | |
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125 | Just to make sure your patch "works", be sure to apply it to the Perl |
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126 | distribution, rebuild everything, and make sure the testsuite runs |
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127 | without incident. |
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128 | |
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129 | =back |
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130 | |
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131 | =head2 What to include in your patch |
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132 | |
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133 | =over 4 |
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134 | |
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135 | =item Description of problem |
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136 | |
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137 | The first thing you should include is a description of the problem that |
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138 | the patch corrects. If it is a code patch (rather than a documentation |
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139 | patch) you should also include a small test case that illustrates the |
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140 | bug. |
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141 | |
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142 | =item Directions for application |
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143 | |
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144 | You should include instructions on how to properly apply your patch. |
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145 | These should include the files affected, any shell scripts or commands |
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146 | that need to be run before or after application of the patch, and |
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147 | the command line necessary for application. |
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148 | |
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149 | =item If you have a code patch |
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150 | |
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151 | If you are submitting a code patch there are several other things that |
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152 | you need to do. |
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153 | |
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154 | =over 4 |
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155 | |
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156 | =item Comments, Comments, Comments |
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157 | |
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158 | Be sure to adequately comment your code. While commenting every |
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159 | line is unnecessary, anything that takes advantage of side effects of |
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160 | operators, that creates changes that will be felt outside of the |
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161 | function being patched, or that others may find confusing should |
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162 | be documented. If you are going to err, it is better to err on the |
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163 | side of adding too many comments than too few. |
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164 | |
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165 | =item Style |
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166 | |
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167 | In general, please follow the particular style of the code you are patching. |
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168 | |
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169 | In particular, follow these general guidelines for patching Perl sources: |
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170 | |
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171 | 8-wide tabs (no exceptions!) |
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172 | 4-wide indents for code, 2-wide indents for nested CPP #defines |
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173 | try hard not to exceed 79-columns |
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174 | ANSI C prototypes |
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175 | uncuddled elses and "K&R" style for indenting control constructs |
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176 | no C++ style (//) comments, most C compilers will choke on them |
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177 | mark places that need to be revisited with XXX (and revisit often!) |
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178 | opening brace lines up with "if" when conditional spans multiple |
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179 | lines; should be at end-of-line otherwise |
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180 | in function definitions, name starts in column 0 (return value is on |
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181 | previous line) |
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182 | single space after keywords that are followed by parens, no space |
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183 | between function name and following paren |
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184 | avoid assignments in conditionals, but if they're unavoidable, use |
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185 | extra paren, e.g. "if (a && (b = c)) ..." |
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186 | "return foo;" rather than "return(foo);" |
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187 | "if (!foo) ..." rather than "if (foo == FALSE) ..." etc. |
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188 | |
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189 | |
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190 | =item Testsuite |
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191 | |
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192 | When submitting a patch you should make every effort to also include |
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193 | an addition to perl's regression tests to properly exercise your |
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194 | patch. Your testsuite additions should generally follow these |
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195 | guidelines (courtesy of Gurusamy Sarathy <gsar@activestate.com>): |
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196 | |
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197 | Know what you're testing. Read the docs, and the source. |
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198 | Tend to fail, not succeed. |
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199 | Interpret results strictly. |
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200 | Use unrelated features (this will flush out bizarre interactions). |
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201 | Use non-standard idioms (otherwise you are not testing TIMTOWTDI). |
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202 | Avoid using hardcoded test numbers whenever possible (the |
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203 | EXPECTED/GOT found in t/op/tie.t is much more maintainable, |
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204 | and gives better failure reports). |
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205 | Give meaningful error messages when a test fails. |
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206 | Avoid using qx// and system() unless you are testing for them. If you |
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207 | do use them, make sure that you cover _all_ perl platforms. |
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208 | Unlink any temporary files you create. |
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209 | Promote unforeseen warnings to errors with $SIG{__WARN__}. |
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210 | Be sure to use the libraries and modules shipped with the version |
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211 | being tested, not those that were already installed. |
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212 | Add comments to the code explaining what you are testing for. |
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213 | Make updating the '1..42' string unnecessary. Or make sure that |
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214 | you update it. |
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215 | Test _all_ behaviors of a given operator, library, or function: |
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216 | - All optional arguments |
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217 | - Return values in various contexts (boolean, scalar, list, lvalue) |
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218 | - Use both global and lexical variables |
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219 | - Don't forget the exceptional, pathological cases. |
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220 | |
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221 | =back |
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222 | |
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223 | =item Test your patch |
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224 | |
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225 | Apply your patch to a clean distribution, compile, and run the |
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226 | regression test suite (you did remember to add one for your |
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227 | patch, didn't you). |
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228 | |
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229 | =back |
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230 | |
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231 | =head2 An example patch creation |
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232 | |
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233 | This should work for most patches: |
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234 | |
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235 | cp MANIFEST MANIFEST.old |
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236 | emacs MANIFEST |
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237 | (make changes) |
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238 | cd .. |
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239 | diff -c perl5.008_42/MANIFEST.old perl5.008_42/MANIFEST > mypatch |
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240 | (testing the patch:) |
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241 | mv perl5.008_42/MANIFEST perl5.008_42/MANIFEST.new |
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242 | cp perl5.008_42/MANIFEST.old perl5.008_42/MANIFEST |
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243 | patch -p < mypatch |
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244 | (should succeed) |
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245 | diff perl5.008_42/MANIFEST perl5.008_42/MANIFEST.new |
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246 | (should produce no output) |
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247 | |
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248 | =head2 Submitting your patch |
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249 | |
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250 | =over 4 |
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251 | |
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252 | =item Mailers |
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253 | |
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254 | Please, please, please (get the point? 8-) don't use a mailer that |
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255 | word wraps your patch or that MIME encodes it. Both of these leave |
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256 | the patch essentially worthless to the maintainer. |
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257 | |
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258 | If you have no choice in mailers and no way to get your hands on a |
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259 | better one there is, of course, a perl solution. Just do this: |
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260 | |
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261 | perl -ne 'print pack("u*",$_)' patch > patch.uue |
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262 | |
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263 | and post patch.uue with a note saying to unpack it using |
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264 | |
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265 | perl -ne 'print unpack("u*",$_)' patch.uue > patch |
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266 | |
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267 | =item Subject lines for patches |
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268 | |
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269 | The subject line on your patch should read |
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270 | |
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271 | [PATCH 5.xxx_xx AREA] Description |
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272 | |
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273 | where the x's are replaced by the appropriate version number. |
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274 | The description should be a very brief but accurate summary of the |
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275 | problem (don't forget this is an email header). |
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276 | |
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277 | Examples: |
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278 | |
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279 | [PATCH 5.004_04 DOC] fix minor typos |
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280 | |
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281 | [PATCH 5.004_99 CORE] New warning for foo() when frobbing |
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282 | |
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283 | [PATCH 5.005_42 CONFIG] Added support for fribnatz 1.5 |
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284 | |
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285 | The name of the file being patched makes for a poor subject line if |
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286 | no other descriptive text accompanies it. |
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287 | |
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288 | =item Where to send your patch |
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289 | |
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290 | If your patch is for a specific bug in the Perl core, it should be sent |
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291 | using the perlbug utility. Don't forget to describe the problem and the |
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292 | fix adequately. |
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293 | |
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294 | If it is a patch to a module that you downloaded from CPAN you should |
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295 | submit your patch to that module's author. |
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296 | |
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297 | If your patch addresses one of the items described in perltodo.pod, |
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298 | please discuss your approach B<before> you make the patch at |
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299 | <perl5-porters@perl.org>. Be sure to browse the archives of past |
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300 | discussions (see perltodo.pod for archive locations). |
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301 | |
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302 | =back |
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303 | |
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304 | =head2 Applying a patch |
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305 | |
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306 | =over 4 |
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307 | |
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308 | =item General notes on applying patches |
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309 | |
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310 | The following are some general notes on applying a patch |
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311 | to your perl distribution. |
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312 | |
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313 | =over 4 |
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314 | |
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315 | =item patch C<-p> |
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316 | |
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317 | It is generally easier to apply patches with the C<-p N> argument to |
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318 | patch (where N is the number of path components to skip in the files |
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319 | found in the headers). This helps reconcile differing paths between |
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320 | the machine the patch was created on and the machine on which it is |
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321 | being applied. |
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322 | |
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323 | =item Cut and paste |
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324 | |
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325 | B<Never> cut and paste a patch into your editor. This usually clobbers |
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326 | the tabs and confuses patch. |
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327 | |
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328 | =item Hand editing patches |
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329 | |
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330 | Avoid hand editing patches as this almost always screws up the line |
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331 | numbers and offsets in the patch, making it useless. |
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332 | |
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333 | =back |
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334 | |
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335 | =back |
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336 | |
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337 | =head2 Final notes |
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338 | |
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339 | If you follow these guidelines it will make everybody's life a little |
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340 | easier. You'll have the satisfaction of having contributed to perl, |
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341 | others will have an easy time using your work, and it should be easier |
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342 | for the maintainers to coordinate the occasionally large numbers of |
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343 | patches received. |
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344 | |
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345 | Also, just because you're not a brilliant coder doesn't mean that you |
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346 | can't contribute. As valuable as code patches are there is always a |
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347 | need for better documentation (especially considering the general |
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348 | level of joy that most programmers feel when forced to sit down and |
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349 | write docs). If all you do is patch the documentation you have still |
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350 | contributed more than the person who sent in an amazing new feature |
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351 | that no one can use because no one understands the code (what I'm |
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352 | getting at is that documentation is both the hardest part to do |
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353 | (because everyone hates doing it) and the most valuable). |
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354 | |
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355 | Mostly, when contributing patches, imagine that it is B<you> receiving |
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356 | hundreds of patches and that it is B<your> responsibility to integrate |
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357 | them into the source. Obviously you'd want the patches to be as easy |
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358 | to apply as possible. Keep that in mind. 8-) |
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359 | |
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360 | =head1 Last Modified |
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361 | |
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362 | Last modified 21 January 1999 |
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363 | Daniel Grisinger <dgris@dimensional.com> |
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364 | |
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365 | =head1 Author and Copyright Information |
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366 | |
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367 | Copyright (c) 1998 Daniel Grisinger |
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368 | |
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369 | Adapted from a posting to perl5-porters by Tim Bunce (Tim.Bunce@ig.co.uk). |
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370 | |
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371 | I'd like to thank the perl5-porters for their suggestions. |
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