1 | =head1 NAME |
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2 | |
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3 | perlfaq3 - Programming Tools ($Revision: 1.1.1.2 $, $Date: 2000-04-07 20:44:20 $) |
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4 | |
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5 | =head1 DESCRIPTION |
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6 | |
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7 | This section of the FAQ answers questions related to programmer tools |
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8 | and programming support. |
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9 | |
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10 | =head2 How do I do (anything)? |
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11 | |
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12 | Have you looked at CPAN (see L<perlfaq2>)? The chances are that |
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13 | someone has already written a module that can solve your problem. |
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14 | Have you read the appropriate man pages? Here's a brief index: |
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15 | |
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16 | Basics perldata, perlvar, perlsyn, perlop, perlsub |
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17 | Execution perlrun, perldebug |
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18 | Functions perlfunc |
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19 | Objects perlref, perlmod, perlobj, perltie |
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20 | Data Structures perlref, perllol, perldsc |
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21 | Modules perlmod, perlmodlib, perlsub |
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22 | Regexes perlre, perlfunc, perlop, perllocale |
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23 | Moving to perl5 perltrap, perl |
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24 | Linking w/C perlxstut, perlxs, perlcall, perlguts, perlembed |
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25 | Various http://www.perl.com/CPAN/doc/FMTEYEWTK/index.html |
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26 | (not a man-page but still useful) |
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27 | |
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28 | A crude table of contents for the Perl man page set is found in L<perltoc>. |
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29 | |
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30 | =head2 How can I use Perl interactively? |
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31 | |
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32 | The typical approach uses the Perl debugger, described in the |
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33 | perldebug(1) man page, on an ``empty'' program, like this: |
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34 | |
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35 | perl -de 42 |
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36 | |
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37 | Now just type in any legal Perl code, and it will be immediately |
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38 | evaluated. You can also examine the symbol table, get stack |
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39 | backtraces, check variable values, set breakpoints, and other |
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40 | operations typically found in symbolic debuggers. |
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41 | |
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42 | =head2 Is there a Perl shell? |
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43 | |
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44 | In general, no. The Shell.pm module (distributed with Perl) makes |
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45 | Perl try commands which aren't part of the Perl language as shell |
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46 | commands. perlsh from the source distribution is simplistic and |
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47 | uninteresting, but may still be what you want. |
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48 | |
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49 | =head2 How do I debug my Perl programs? |
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50 | |
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51 | Have you tried C<use warnings> or used C<-w>? They enable warnings |
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52 | for dubious practices. |
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53 | |
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54 | Have you tried C<use strict>? It prevents you from using symbolic |
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55 | references, makes you predeclare any subroutines that you call as bare |
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56 | words, and (probably most importantly) forces you to predeclare your |
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57 | variables with C<my> or C<our> or C<use vars>. |
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58 | |
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59 | Did you check the returns of each and every system call? The operating |
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60 | system (and thus Perl) tells you whether they worked or not, and if not |
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61 | why. |
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62 | |
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63 | open(FH, "> /etc/cantwrite") |
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64 | or die "Couldn't write to /etc/cantwrite: $!\n"; |
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65 | |
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66 | Did you read L<perltrap>? It's full of gotchas for old and new Perl |
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67 | programmers, and even has sections for those of you who are upgrading |
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68 | from languages like I<awk> and I<C>. |
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69 | |
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70 | Have you tried the Perl debugger, described in L<perldebug>? You can |
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71 | step through your program and see what it's doing and thus work out |
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72 | why what it's doing isn't what it should be doing. |
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73 | |
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74 | =head2 How do I profile my Perl programs? |
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75 | |
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76 | You should get the Devel::DProf module from CPAN, and also use |
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77 | Benchmark.pm from the standard distribution. Benchmark lets you time |
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78 | specific portions of your code, while Devel::DProf gives detailed |
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79 | breakdowns of where your code spends its time. |
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80 | |
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81 | Here's a sample use of Benchmark: |
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82 | |
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83 | use Benchmark; |
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84 | |
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85 | @junk = `cat /etc/motd`; |
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86 | $count = 10_000; |
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87 | |
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88 | timethese($count, { |
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89 | 'map' => sub { my @a = @junk; |
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90 | map { s/a/b/ } @a; |
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91 | return @a |
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92 | }, |
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93 | 'for' => sub { my @a = @junk; |
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94 | local $_; |
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95 | for (@a) { s/a/b/ }; |
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96 | return @a }, |
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97 | }); |
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98 | |
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99 | This is what it prints (on one machine--your results will be dependent |
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100 | on your hardware, operating system, and the load on your machine): |
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101 | |
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102 | Benchmark: timing 10000 iterations of for, map... |
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103 | for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu) |
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104 | map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu) |
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105 | |
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106 | Be aware that a good benchmark is very hard to write. It only tests the |
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107 | data you give it, and really proves little about differing complexities |
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108 | of contrasting algorithms. |
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109 | |
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110 | =head2 How do I cross-reference my Perl programs? |
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111 | |
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112 | The B::Xref module, shipped with the new, alpha-release Perl compiler |
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113 | (not the general distribution prior to the 5.005 release), can be used |
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114 | to generate cross-reference reports for Perl programs. |
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115 | |
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116 | perl -MO=Xref[,OPTIONS] scriptname.plx |
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117 | |
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118 | =head2 Is there a pretty-printer (formatter) for Perl? |
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119 | |
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120 | There is no program that will reformat Perl as much as indent(1) does |
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121 | for C. The complex feedback between the scanner and the parser (this |
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122 | feedback is what confuses the vgrind and emacs programs) makes it |
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123 | challenging at best to write a stand-alone Perl parser. |
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124 | |
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125 | Of course, if you simply follow the guidelines in L<perlstyle>, you |
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126 | shouldn't need to reformat. The habit of formatting your code as you |
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127 | write it will help prevent bugs. Your editor can and should help you |
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128 | with this. The perl-mode for emacs can provide a remarkable amount of |
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129 | help with most (but not all) code, and even less programmable editors |
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130 | can provide significant assistance. Tom swears by the following |
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131 | settings in vi and its clones: |
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132 | |
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133 | set ai sw=4 |
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134 | map! ^O {^M}^[O^T |
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135 | |
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136 | Now put that in your F<.exrc> file (replacing the caret characters |
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137 | with control characters) and away you go. In insert mode, ^T is |
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138 | for indenting, ^D is for undenting, and ^O is for blockdenting -- |
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139 | as it were. If you haven't used the last one, you're missing |
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140 | a lot. A more complete example, with comments, can be found at |
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141 | http://www.perl.com/CPAN-local/authors/id/TOMC/scripts/toms.exrc.gz |
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142 | |
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143 | If you are used to using the I<vgrind> program for printing out nice code |
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144 | to a laser printer, you can take a stab at this using |
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145 | http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the |
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146 | results are not particularly satisfying for sophisticated code. |
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147 | |
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148 | The a2ps at http://www.infres.enst.fr/%7Edemaille/a2ps/ does lots of things |
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149 | related to generating nicely printed output of documents. |
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150 | |
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151 | =head2 Is there a ctags for Perl? |
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152 | |
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153 | There's a simple one at |
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154 | http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do |
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155 | the trick. And if not, it's easy to hack into what you want. |
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156 | |
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157 | =head2 Is there an IDE or Windows Perl Editor? |
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158 | |
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159 | If you're on Unix, you already have an IDE -- Unix itself. This powerful |
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160 | IDE derives from its interoperability, flexibility, and configurability. |
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161 | If you really want to get a feel for Unix-qua-IDE, the best thing to do |
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162 | is to find some high-powered programmer whose native language is Unix. |
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163 | Find someone who has been at this for many years, and just sit back |
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164 | and watch them at work. They have created their own IDE, one that |
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165 | suits their own tastes and aptitudes. Quietly observe them edit files, |
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166 | move them around, compile them, debug them, test them, etc. The entire |
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167 | development *is* integrated, like a top-of-the-line German sports car: |
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168 | functional, powerful, and elegant. You will be absolutely astonished |
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169 | at the speed and ease exhibited by the native speaker of Unix in his |
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170 | home territory. The art and skill of a virtuoso can only be seen to be |
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171 | believed. That is the path to mastery -- all these cobbled little IDEs |
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172 | are expensive toys designed to sell a flashy demo using cheap tricks, |
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173 | and being optimized for immediate but shallow understanding rather than |
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174 | enduring use, are but a dim palimpsest of real tools. |
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175 | |
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176 | In short, you just have to learn the toolbox. However, if you're not |
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177 | on Unix, then your vendor probably didn't bother to provide you with |
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178 | a proper toolbox on the so-called complete system that you forked out |
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179 | your hard-earned cash on. |
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180 | |
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181 | PerlBuilder (XXX URL to follow) is an integrated development environment |
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182 | for Windows that supports Perl development. Perl programs are just plain |
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183 | text, though, so you could download emacs for Windows (???) or a vi clone |
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184 | (vim) which runs on for win32 (http://www.cs.vu.nl/%7Etmgil/vi.html). |
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185 | If you're transferring Windows files to Unix, be sure to transfer in |
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186 | ASCII mode so the ends of lines are appropriately mangled. |
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187 | |
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188 | =head2 Where can I get Perl macros for vi? |
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189 | |
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190 | For a complete version of Tom Christiansen's vi configuration file, |
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191 | see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz, |
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192 | the standard benchmark file for vi emulators. This runs best with nvi, |
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193 | the current version of vi out of Berkeley, which incidentally can be built |
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194 | with an embedded Perl interpreter -- see http://www.perl.com/CPAN/src/misc. |
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195 | |
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196 | =head2 Where can I get perl-mode for emacs? |
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197 | |
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198 | Since Emacs version 19 patchlevel 22 or so, there have been both a |
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199 | perl-mode.el and support for the Perl debugger built in. These should |
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200 | come with the standard Emacs 19 distribution. |
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201 | |
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202 | In the Perl source directory, you'll find a directory called "emacs", |
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203 | which contains a cperl-mode that color-codes keywords, provides |
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204 | context-sensitive help, and other nifty things. |
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205 | |
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206 | Note that the perl-mode of emacs will have fits with C<"main'foo"> |
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207 | (single quote), and mess up the indentation and highlighting. You |
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208 | are probably using C<"main::foo"> in new Perl code anyway, so this |
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209 | shouldn't be an issue. |
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210 | |
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211 | =head2 How can I use curses with Perl? |
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212 | |
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213 | The Curses module from CPAN provides a dynamically loadable object |
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214 | module interface to a curses library. A small demo can be found at the |
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215 | directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep; |
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216 | this program repeats a command and updates the screen as needed, rendering |
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217 | B<rep ps axu> similar to B<top>. |
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218 | |
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219 | =head2 How can I use X or Tk with Perl? |
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220 | |
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221 | Tk is a completely Perl-based, object-oriented interface to the Tk toolkit |
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222 | that doesn't force you to use Tcl just to get at Tk. Sx is an interface |
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223 | to the Athena Widget set. Both are available from CPAN. See the |
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224 | directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/ |
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225 | |
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226 | Invaluable for Perl/Tk programming are: the Perl/Tk FAQ at |
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227 | http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference |
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228 | Guide available at |
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229 | http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the |
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230 | online manpages at |
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231 | http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html . |
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232 | |
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233 | =head2 How can I generate simple menus without using CGI or Tk? |
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234 | |
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235 | The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz |
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236 | module, which is curses-based, can help with this. |
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237 | |
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238 | =head2 What is undump? |
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239 | |
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240 | See the next questions. |
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241 | |
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242 | =head2 How can I make my Perl program run faster? |
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243 | |
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244 | The best way to do this is to come up with a better algorithm. This |
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245 | can often make a dramatic difference. Chapter 8 in the Camel has some |
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246 | efficiency tips in it you might want to look at. Jon Bentley's book |
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247 | ``Programming Pearls'' (that's not a misspelling!) has some good tips |
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248 | on optimization, too. Advice on benchmarking boils down to: benchmark |
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249 | and profile to make sure you're optimizing the right part, look for |
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250 | better algorithms instead of microtuning your code, and when all else |
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251 | fails consider just buying faster hardware. |
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252 | |
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253 | A different approach is to autoload seldom-used Perl code. See the |
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254 | AutoSplit and AutoLoader modules in the standard distribution for |
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255 | that. Or you could locate the bottleneck and think about writing just |
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256 | that part in C, the way we used to take bottlenecks in C code and |
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257 | write them in assembler. Similar to rewriting in C is the use of |
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258 | modules that have critical sections written in C (for instance, the |
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259 | PDL module from CPAN). |
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260 | |
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261 | In some cases, it may be worth it to use the backend compiler to |
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262 | produce byte code (saving compilation time) or compile into C, which |
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263 | will certainly save compilation time and sometimes a small amount (but |
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264 | not much) execution time. See the question about compiling your Perl |
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265 | programs for more on the compiler--the wins aren't as obvious as you'd |
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266 | hope. |
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267 | |
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268 | If you're currently linking your perl executable to a shared I<libc.so>, |
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269 | you can often gain a 10-25% performance benefit by rebuilding it to |
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270 | link with a static libc.a instead. This will make a bigger perl |
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271 | executable, but your Perl programs (and programmers) may thank you for |
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272 | it. See the F<INSTALL> file in the source distribution for more |
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273 | information. |
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274 | |
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275 | Unsubstantiated reports allege that Perl interpreters that use sfio |
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276 | outperform those that don't (for I/O intensive applications). To try |
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277 | this, see the F<INSTALL> file in the source distribution, especially |
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278 | the ``Selecting File I/O mechanisms'' section. |
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279 | |
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280 | The undump program was an old attempt to speed up your Perl program |
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281 | by storing the already-compiled form to disk. This is no longer |
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282 | a viable option, as it only worked on a few architectures, and |
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283 | wasn't a good solution anyway. |
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284 | |
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285 | =head2 How can I make my Perl program take less memory? |
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286 | |
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287 | When it comes to time-space tradeoffs, Perl nearly always prefers to |
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288 | throw memory at a problem. Scalars in Perl use more memory than |
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289 | strings in C, arrays take more than that, and hashes use even more. While |
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290 | there's still a lot to be done, recent releases have been addressing |
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291 | these issues. For example, as of 5.004, duplicate hash keys are |
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292 | shared amongst all hashes using them, so require no reallocation. |
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293 | |
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294 | In some cases, using substr() or vec() to simulate arrays can be |
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295 | highly beneficial. For example, an array of a thousand booleans will |
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296 | take at least 20,000 bytes of space, but it can be turned into one |
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297 | 125-byte bit vector for a considerable memory savings. The standard |
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298 | Tie::SubstrHash module can also help for certain types of data |
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299 | structure. If you're working with specialist data structures |
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300 | (matrices, for instance) modules that implement these in C may use |
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301 | less memory than equivalent Perl modules. |
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302 | |
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303 | Another thing to try is learning whether your Perl was compiled with |
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304 | the system malloc or with Perl's builtin malloc. Whichever one it |
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305 | is, try using the other one and see whether this makes a difference. |
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306 | Information about malloc is in the F<INSTALL> file in the source |
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307 | distribution. You can find out whether you are using perl's malloc by |
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308 | typing C<perl -V:usemymalloc>. |
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309 | |
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310 | =head2 Is it unsafe to return a pointer to local data? |
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311 | |
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312 | No, Perl's garbage collection system takes care of this. |
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313 | |
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314 | sub makeone { |
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315 | my @a = ( 1 .. 10 ); |
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316 | return \@a; |
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317 | } |
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318 | |
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319 | for $i ( 1 .. 10 ) { |
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320 | push @many, makeone(); |
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321 | } |
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322 | |
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323 | print $many[4][5], "\n"; |
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324 | |
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325 | print "@many\n"; |
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326 | |
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327 | =head2 How can I free an array or hash so my program shrinks? |
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328 | |
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329 | You can't. On most operating systems, memory allocated to a program |
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330 | can never be returned to the system. That's why long-running programs |
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331 | sometimes re-exec themselves. Some operating systems (notably, |
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332 | FreeBSD and Linux) allegedly reclaim large chunks of memory that is no |
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333 | longer used, but it doesn't appear to happen with Perl (yet). The Mac |
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334 | appears to be the only platform that will reliably (albeit, slowly) |
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335 | return memory to the OS. |
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336 | |
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337 | We've had reports that on Linux (Redhat 5.1) on Intel, C<undef |
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338 | $scalar> will return memory to the system, while on Solaris 2.6 it |
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339 | won't. In general, try it yourself and see. |
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340 | |
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341 | However, judicious use of my() on your variables will help make sure |
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342 | that they go out of scope so that Perl can free up their storage for |
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343 | use in other parts of your program. A global variable, of course, never |
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344 | goes out of scope, so you can't get its space automatically reclaimed, |
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345 | although undef()ing and/or delete()ing it will achieve the same effect. |
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346 | In general, memory allocation and de-allocation isn't something you can |
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347 | or should be worrying about much in Perl, but even this capability |
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348 | (preallocation of data types) is in the works. |
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349 | |
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350 | =head2 How can I make my CGI script more efficient? |
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351 | |
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352 | Beyond the normal measures described to make general Perl programs |
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353 | faster or smaller, a CGI program has additional issues. It may be run |
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354 | several times per second. Given that each time it runs it will need |
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355 | to be re-compiled and will often allocate a megabyte or more of system |
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356 | memory, this can be a killer. Compiling into C B<isn't going to help |
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357 | you> because the process start-up overhead is where the bottleneck is. |
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358 | |
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359 | There are two popular ways to avoid this overhead. One solution |
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360 | involves running the Apache HTTP server (available from |
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361 | http://www.apache.org/) with either of the mod_perl or mod_fastcgi |
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362 | plugin modules. |
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363 | |
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364 | With mod_perl and the Apache::Registry module (distributed with |
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365 | mod_perl), httpd will run with an embedded Perl interpreter which |
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366 | pre-compiles your script and then executes it within the same address |
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367 | space without forking. The Apache extension also gives Perl access to |
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368 | the internal server API, so modules written in Perl can do just about |
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369 | anything a module written in C can. For more on mod_perl, see |
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370 | http://perl.apache.org/ |
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371 | |
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372 | With the FCGI module (from CPAN) and the mod_fastcgi |
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373 | module (available from http://www.fastcgi.com/) each of your Perl |
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374 | programs becomes a permanent CGI daemon process. |
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375 | |
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376 | Both of these solutions can have far-reaching effects on your system |
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377 | and on the way you write your CGI programs, so investigate them with |
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378 | care. |
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379 | |
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380 | See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ . |
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381 | |
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382 | A non-free, commercial product, ``The Velocity Engine for Perl'', |
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383 | (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/) might |
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384 | also be worth looking at. It will allow you to increase the performance |
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385 | of your Perl programs, up to 25 times faster than normal CGI Perl by |
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386 | running in persistent Perl mode, or 4 to 5 times faster without any |
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387 | modification to your existing CGI programs. Fully functional evaluation |
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388 | copies are available from the web site. |
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389 | |
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390 | =head2 How can I hide the source for my Perl program? |
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391 | |
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392 | Delete it. :-) Seriously, there are a number of (mostly |
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393 | unsatisfactory) solutions with varying levels of ``security''. |
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394 | |
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395 | First of all, however, you I<can't> take away read permission, because |
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396 | the source code has to be readable in order to be compiled and |
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397 | interpreted. (That doesn't mean that a CGI script's source is |
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398 | readable by people on the web, though, only by people with access to |
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399 | the filesystem) So you have to leave the permissions at the socially |
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400 | friendly 0755 level. |
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401 | |
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402 | Some people regard this as a security problem. If your program does |
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403 | insecure things, and relies on people not knowing how to exploit those |
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404 | insecurities, it is not secure. It is often possible for someone to |
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405 | determine the insecure things and exploit them without viewing the |
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406 | source. Security through obscurity, the name for hiding your bugs |
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407 | instead of fixing them, is little security indeed. |
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408 | |
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409 | You can try using encryption via source filters (Filter::* from CPAN), |
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410 | but any decent programmer will be able to decrypt it. You can try using |
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411 | the byte code compiler and interpreter described below, but the curious |
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412 | might still be able to de-compile it. You can try using the native-code |
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413 | compiler described below, but crackers might be able to disassemble it. |
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414 | These pose varying degrees of difficulty to people wanting to get at |
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415 | your code, but none can definitively conceal it (this is true of every |
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416 | language, not just Perl). |
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417 | |
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418 | If you're concerned about people profiting from your code, then the |
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419 | bottom line is that nothing but a restrictive license will give you |
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420 | legal security. License your software and pepper it with threatening |
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421 | statements like ``This is unpublished proprietary software of XYZ Corp. |
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422 | Your access to it does not give you permission to use it blah blah |
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423 | blah.'' We are not lawyers, of course, so you should see a lawyer if |
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424 | you want to be sure your license's wording will stand up in court. |
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425 | |
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426 | =head2 How can I compile my Perl program into byte code or C? |
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427 | |
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428 | Malcolm Beattie has written a multifunction backend compiler, |
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429 | available from CPAN, that can do both these things. It is included |
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430 | in the perl5.005 release, but is still considered experimental. |
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431 | This means it's fun to play with if you're a programmer but not |
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432 | really for people looking for turn-key solutions. |
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433 | |
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434 | Merely compiling into C does not in and of itself guarantee that your |
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435 | code will run very much faster. That's because except for lucky cases |
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436 | where a lot of native type inferencing is possible, the normal Perl |
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437 | run time system is still present and so your program will take just as |
---|
438 | long to run and be just as big. Most programs save little more than |
---|
439 | compilation time, leaving execution no more than 10-30% faster. A few |
---|
440 | rare programs actually benefit significantly (like several times |
---|
441 | faster), but this takes some tweaking of your code. |
---|
442 | |
---|
443 | You'll probably be astonished to learn that the current version of the |
---|
444 | compiler generates a compiled form of your script whose executable is |
---|
445 | just as big as the original perl executable, and then some. That's |
---|
446 | because as currently written, all programs are prepared for a full |
---|
447 | eval() statement. You can tremendously reduce this cost by building a |
---|
448 | shared I<libperl.so> library and linking against that. See the |
---|
449 | F<INSTALL> podfile in the Perl source distribution for details. If |
---|
450 | you link your main perl binary with this, it will make it minuscule. |
---|
451 | For example, on one author's system, F</usr/bin/perl> is only 11k in |
---|
452 | size! |
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453 | |
---|
454 | In general, the compiler will do nothing to make a Perl program smaller, |
---|
455 | faster, more portable, or more secure. In fact, it will usually hurt |
---|
456 | all of those. The executable will be bigger, your VM system may take |
---|
457 | longer to load the whole thing, the binary is fragile and hard to fix, |
---|
458 | and compilation never stopped software piracy in the form of crackers, |
---|
459 | viruses, or bootleggers. The real advantage of the compiler is merely |
---|
460 | packaging, and once you see the size of what it makes (well, unless |
---|
461 | you use a shared I<libperl.so>), you'll probably want a complete |
---|
462 | Perl install anyway. |
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463 | |
---|
464 | =head2 How can I compile Perl into Java? |
---|
465 | |
---|
466 | You can't. Not yet, anyway. You can integrate Java and Perl with the |
---|
467 | Perl Resource Kit from O'Reilly and Associates. See |
---|
468 | http://www.oreilly.com/catalog/prkunix/ for more information. |
---|
469 | The Java interface will be supported in the core 5.6 release |
---|
470 | of Perl. |
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471 | |
---|
472 | =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]? |
---|
473 | |
---|
474 | For OS/2 just use |
---|
475 | |
---|
476 | extproc perl -S -your_switches |
---|
477 | |
---|
478 | as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's |
---|
479 | `extproc' handling). For DOS one should first invent a corresponding |
---|
480 | batch file, and codify it in C<ALTERNATIVE_SHEBANG> (see the |
---|
481 | F<INSTALL> file in the source distribution for more information). |
---|
482 | |
---|
483 | The Win95/NT installation, when using the ActiveState port of Perl, |
---|
484 | will modify the Registry to associate the C<.pl> extension with the |
---|
485 | perl interpreter. If you install another port, perhaps even building |
---|
486 | your own Win95/NT Perl from the standard sources by using a Windows port |
---|
487 | of gcc (e.g., with cygwin or mingw32), then you'll have to modify |
---|
488 | the Registry yourself. In addition to associating C<.pl> with the |
---|
489 | interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them |
---|
490 | run the program C<install-linux.pl> merely by typing C<install-linux>. |
---|
491 | |
---|
492 | Macintosh Perl programs will have the appropriate Creator and |
---|
493 | Type, so that double-clicking them will invoke the Perl application. |
---|
494 | |
---|
495 | I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just |
---|
496 | throw the perl interpreter into your cgi-bin directory, in order to |
---|
497 | get your programs working for a web server. This is an EXTREMELY big |
---|
498 | security risk. Take the time to figure out how to do it correctly. |
---|
499 | |
---|
500 | =head2 Can I write useful Perl programs on the command line? |
---|
501 | |
---|
502 | Yes. Read L<perlrun> for more information. Some examples follow. |
---|
503 | (These assume standard Unix shell quoting rules.) |
---|
504 | |
---|
505 | # sum first and last fields |
---|
506 | perl -lane 'print $F[0] + $F[-1]' * |
---|
507 | |
---|
508 | # identify text files |
---|
509 | perl -le 'for(@ARGV) {print if -f && -T _}' * |
---|
510 | |
---|
511 | # remove (most) comments from C program |
---|
512 | perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c |
---|
513 | |
---|
514 | # make file a month younger than today, defeating reaper daemons |
---|
515 | perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' * |
---|
516 | |
---|
517 | # find first unused uid |
---|
518 | perl -le '$i++ while getpwuid($i); print $i' |
---|
519 | |
---|
520 | # display reasonable manpath |
---|
521 | echo $PATH | perl -nl -072 -e ' |
---|
522 | s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}' |
---|
523 | |
---|
524 | OK, the last one was actually an Obfuscated Perl Contest entry. :-) |
---|
525 | |
---|
526 | =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system? |
---|
527 | |
---|
528 | The problem is usually that the command interpreters on those systems |
---|
529 | have rather different ideas about quoting than the Unix shells under |
---|
530 | which the one-liners were created. On some systems, you may have to |
---|
531 | change single-quotes to double ones, which you must I<NOT> do on Unix |
---|
532 | or Plan9 systems. You might also have to change a single % to a %%. |
---|
533 | |
---|
534 | For example: |
---|
535 | |
---|
536 | # Unix |
---|
537 | perl -e 'print "Hello world\n"' |
---|
538 | |
---|
539 | # DOS, etc. |
---|
540 | perl -e "print \"Hello world\n\"" |
---|
541 | |
---|
542 | # Mac |
---|
543 | print "Hello world\n" |
---|
544 | (then Run "Myscript" or Shift-Command-R) |
---|
545 | |
---|
546 | # VMS |
---|
547 | perl -e "print ""Hello world\n""" |
---|
548 | |
---|
549 | The problem is that none of this is reliable: it depends on the |
---|
550 | command interpreter. Under Unix, the first two often work. Under DOS, |
---|
551 | it's entirely possible neither works. If 4DOS was the command shell, |
---|
552 | you'd probably have better luck like this: |
---|
553 | |
---|
554 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" |
---|
555 | |
---|
556 | Under the Mac, it depends which environment you are using. The MacPerl |
---|
557 | shell, or MPW, is much like Unix shells in its support for several |
---|
558 | quoting variants, except that it makes free use of the Mac's non-ASCII |
---|
559 | characters as control characters. |
---|
560 | |
---|
561 | Using qq(), q(), and qx(), instead of "double quotes", 'single |
---|
562 | quotes', and `backticks`, may make one-liners easier to write. |
---|
563 | |
---|
564 | There is no general solution to all of this. It is a mess, pure and |
---|
565 | simple. Sucks to be away from Unix, huh? :-) |
---|
566 | |
---|
567 | [Some of this answer was contributed by Kenneth Albanowski.] |
---|
568 | |
---|
569 | =head2 Where can I learn about CGI or Web programming in Perl? |
---|
570 | |
---|
571 | For modules, get the CGI or LWP modules from CPAN. For textbooks, |
---|
572 | see the two especially dedicated to web stuff in the question on |
---|
573 | books. For problems and questions related to the web, like ``Why |
---|
574 | do I get 500 Errors'' or ``Why doesn't it run from the browser right |
---|
575 | when it runs fine on the command line'', see these sources: |
---|
576 | |
---|
577 | WWW Security FAQ |
---|
578 | http://www.w3.org/Security/Faq/ |
---|
579 | |
---|
580 | Web FAQ |
---|
581 | http://www.boutell.com/faq/ |
---|
582 | |
---|
583 | CGI FAQ |
---|
584 | http://www.webthing.com/tutorials/cgifaq.html |
---|
585 | |
---|
586 | HTTP Spec |
---|
587 | http://www.w3.org/pub/WWW/Protocols/HTTP/ |
---|
588 | |
---|
589 | HTML Spec |
---|
590 | http://www.w3.org/TR/REC-html40/ |
---|
591 | http://www.w3.org/pub/WWW/MarkUp/ |
---|
592 | |
---|
593 | CGI Spec |
---|
594 | http://www.w3.org/CGI/ |
---|
595 | |
---|
596 | CGI Security FAQ |
---|
597 | http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt |
---|
598 | |
---|
599 | |
---|
600 | =head2 Where can I learn about object-oriented Perl programming? |
---|
601 | |
---|
602 | A good place to start is L<perltoot>, and you can use L<perlobj> and |
---|
603 | L<perlbot> for reference. Perltoot didn't come out until the 5.004 |
---|
604 | release, but you can get a copy (in pod, html, or postscript) from |
---|
605 | http://www.perl.com/CPAN/doc/FMTEYEWTK/ . |
---|
606 | |
---|
607 | =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp] |
---|
608 | |
---|
609 | If you want to call C from Perl, start with L<perlxstut>, |
---|
610 | moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to |
---|
611 | call Perl from C, then read L<perlembed>, L<perlcall>, and |
---|
612 | L<perlguts>. Don't forget that you can learn a lot from looking at |
---|
613 | how the authors of existing extension modules wrote their code and |
---|
614 | solved their problems. |
---|
615 | |
---|
616 | =head2 I've read perlembed, perlguts, etc., but I can't embed perl in |
---|
617 | my C program, what am I doing wrong? |
---|
618 | |
---|
619 | Download the ExtUtils::Embed kit from CPAN and run `make test'. If |
---|
620 | the tests pass, read the pods again and again and again. If they |
---|
621 | fail, see L<perlbug> and send a bug report with the output of |
---|
622 | C<make test TEST_VERBOSE=1> along with C<perl -V>. |
---|
623 | |
---|
624 | =head2 When I tried to run my script, I got this message. What does it |
---|
625 | mean? |
---|
626 | |
---|
627 | A complete list of Perl's error messages and warnings with explanatory |
---|
628 | text can be found in L<perldiag>. You can also use the splain program |
---|
629 | (distributed with Perl) to explain the error messages: |
---|
630 | |
---|
631 | perl program 2>diag.out |
---|
632 | splain [-v] [-p] diag.out |
---|
633 | |
---|
634 | or change your program to explain the messages for you: |
---|
635 | |
---|
636 | use diagnostics; |
---|
637 | |
---|
638 | or |
---|
639 | |
---|
640 | use diagnostics -verbose; |
---|
641 | |
---|
642 | =head2 What's MakeMaker? |
---|
643 | |
---|
644 | This module (part of the standard Perl distribution) is designed to |
---|
645 | write a Makefile for an extension module from a Makefile.PL. For more |
---|
646 | information, see L<ExtUtils::MakeMaker>. |
---|
647 | |
---|
648 | =head1 AUTHOR AND COPYRIGHT |
---|
649 | |
---|
650 | Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington. |
---|
651 | All rights reserved. |
---|
652 | |
---|
653 | When included as an integrated part of the Standard Distribution |
---|
654 | of Perl or of its documentation (printed or otherwise), this works is |
---|
655 | covered under Perl's Artistic License. For separate distributions of |
---|
656 | all or part of this FAQ outside of that, see L<perlfaq>. |
---|
657 | |
---|
658 | Irrespective of its distribution, all code examples here are in the public |
---|
659 | domain. You are permitted and encouraged to use this code and any |
---|
660 | derivatives thereof in your own programs for fun or for profit as you |
---|
661 | see fit. A simple comment in the code giving credit to the FAQ would |
---|
662 | be courteous but is not required. |
---|