1 | =head1 NAME
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2 |
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3 | perlfaq3 - Programming Tools ($Revision: 1.56 $, $Date: 2005/12/31 00:54:37 $)
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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 manpages? 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.cpan.org/misc/olddoc/FMTEYEWTK.tgz
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26 | (not a man-page but still useful, a collection
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27 | of various essays on Perl techniques)
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28 |
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29 | A crude table of contents for the Perl manpage set is found in L<perltoc>.
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30 |
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31 | =head2 How can I use Perl interactively?
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32 |
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33 | The typical approach uses the Perl debugger, described in the
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34 | perldebug(1) manpage, on an "empty" program, like this:
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35 |
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36 | perl -de 42
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37 |
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38 | Now just type in any legal Perl code, and it will be immediately
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39 | evaluated. You can also examine the symbol table, get stack
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40 | backtraces, check variable values, set breakpoints, and other
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41 | operations typically found in symbolic debuggers.
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42 |
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43 | =head2 Is there a Perl shell?
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44 |
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45 | The psh (Perl sh) is currently at version 1.8. The Perl Shell is a shell
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46 | that combines the interactive nature of a Unix shell with the power of
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47 | Perl. The goal is a full featured shell that behaves as expected for
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48 | normal shell activity and uses Perl syntax and functionality for
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49 | control-flow statements and other things. You can get psh at
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50 | http://sourceforge.net/projects/psh/ .
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51 |
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52 | Zoidberg is a similar project and provides a shell written in perl,
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53 | configured in perl and operated in perl. It is intended as a login shell
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54 | and development environment. It can be found at http://zoidberg.sf.net/
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55 | or your local CPAN mirror.
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56 |
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57 | The Shell.pm module (distributed with Perl) makes Perl try commands
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58 | which aren't part of the Perl language as shell commands. perlsh from
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59 | the source distribution is simplistic and uninteresting, but may still
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60 | be what you want.
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61 |
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62 | =head2 How do I find which modules are installed on my system?
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63 |
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64 | You can use the ExtUtils::Installed module to show all installed
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65 | distributions, although it can take awhile to do its magic. The
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66 | standard library which comes with Perl just shows up as "Perl" (although
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67 | you can get those with Module::CoreList).
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68 |
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69 | use ExtUtils::Installed;
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70 |
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71 | my $inst = ExtUtils::Installed->new();
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72 | my @modules = $inst->modules();
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73 |
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74 | If you want a list of all of the Perl module filenames, you
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75 | can use File::Find::Rule.
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76 |
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77 | use File::Find::Rule;
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78 |
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79 | my @files = File::Find::Rule->file()->name( '*.pm' )->in( @INC );
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80 |
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81 | If you do not have that module, you can do the same thing
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82 | with File::Find which is part of the standard library.
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83 |
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84 | use File::Find;
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85 | my @files;
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86 |
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87 | find(
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88 | sub {
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89 | push @files, $File::Find::name
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90 | if -f $File::Find::name && /\.pm$/
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91 | },
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92 |
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93 | @INC
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94 | );
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95 |
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96 | print join "\n", @files;
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97 |
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98 | If you simply need to quickly check to see if a module is
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99 | available, you can check for its documentation. If you can
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100 | read the documentation the module is most likely installed.
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101 | If you cannot read the documentation, the module might not
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102 | have any (in rare cases).
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103 |
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104 | prompt% perldoc Module::Name
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105 |
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106 | You can also try to include the module in a one-liner to see if
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107 | perl finds it.
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108 |
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109 | perl -MModule::Name -e1
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110 |
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111 | =head2 How do I debug my Perl programs?
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112 |
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113 | Have you tried C<use warnings> or used C<-w>? They enable warnings
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114 | to detect dubious practices.
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115 |
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116 | Have you tried C<use strict>? It prevents you from using symbolic
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117 | references, makes you predeclare any subroutines that you call as bare
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118 | words, and (probably most importantly) forces you to predeclare your
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119 | variables with C<my>, C<our>, or C<use vars>.
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120 |
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121 | Did you check the return values of each and every system call? The operating
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122 | system (and thus Perl) tells you whether they worked, and if not
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123 | why.
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124 |
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125 | open(FH, "> /etc/cantwrite")
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126 | or die "Couldn't write to /etc/cantwrite: $!\n";
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127 |
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128 | Did you read L<perltrap>? It's full of gotchas for old and new Perl
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129 | programmers and even has sections for those of you who are upgrading
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130 | from languages like I<awk> and I<C>.
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131 |
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132 | Have you tried the Perl debugger, described in L<perldebug>? You can
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133 | step through your program and see what it's doing and thus work out
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134 | why what it's doing isn't what it should be doing.
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135 |
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136 | =head2 How do I profile my Perl programs?
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137 |
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138 | You should get the Devel::DProf module from the standard distribution
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139 | (or separately on CPAN) and also use Benchmark.pm from the standard
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140 | distribution. The Benchmark module lets you time specific portions of
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141 | your code, while Devel::DProf gives detailed breakdowns of where your
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142 | code spends its time.
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143 |
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144 | Here's a sample use of Benchmark:
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145 |
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146 | use Benchmark;
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147 |
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148 | @junk = `cat /etc/motd`;
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149 | $count = 10_000;
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150 |
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151 | timethese($count, {
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152 | 'map' => sub { my @a = @junk;
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153 | map { s/a/b/ } @a;
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154 | return @a },
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155 | 'for' => sub { my @a = @junk;
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156 | for (@a) { s/a/b/ };
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157 | return @a },
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158 | });
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159 |
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160 | This is what it prints (on one machine--your results will be dependent
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161 | on your hardware, operating system, and the load on your machine):
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162 |
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163 | Benchmark: timing 10000 iterations of for, map...
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164 | for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu)
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165 | map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu)
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166 |
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167 | Be aware that a good benchmark is very hard to write. It only tests the
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168 | data you give it and proves little about the differing complexities
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169 | of contrasting algorithms.
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170 |
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171 | =head2 How do I cross-reference my Perl programs?
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172 |
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173 | The B::Xref module can be used to generate cross-reference reports
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174 | for Perl programs.
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175 |
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176 | perl -MO=Xref[,OPTIONS] scriptname.plx
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177 |
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178 | =head2 Is there a pretty-printer (formatter) for Perl?
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179 |
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180 | Perltidy is a Perl script which indents and reformats Perl scripts
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181 | to make them easier to read by trying to follow the rules of the
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182 | L<perlstyle>. If you write Perl scripts, or spend much time reading
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183 | them, you will probably find it useful. It is available at
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184 | http://perltidy.sourceforge.net
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185 |
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186 | Of course, if you simply follow the guidelines in L<perlstyle>,
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187 | you shouldn't need to reformat. The habit of formatting your code
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188 | as you write it will help prevent bugs. Your editor can and should
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189 | help you with this. The perl-mode or newer cperl-mode for emacs
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190 | can provide remarkable amounts of help with most (but not all)
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191 | code, and even less programmable editors can provide significant
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192 | assistance. Tom Christiansen and many other VI users swear by
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193 | the following settings in vi and its clones:
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194 |
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195 | set ai sw=4
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196 | map! ^O {^M}^[O^T
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197 |
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198 | Put that in your F<.exrc> file (replacing the caret characters
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199 | with control characters) and away you go. In insert mode, ^T is
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200 | for indenting, ^D is for undenting, and ^O is for blockdenting--
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201 | as it were. A more complete example, with comments, can be found at
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202 | http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz
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203 |
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204 | The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps.gz does
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205 | lots of things related to generating nicely printed output of
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206 | documents, as does enscript at http://people.ssh.fi/mtr/genscript/ .
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207 |
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208 | =head2 Is there a ctags for Perl?
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209 |
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210 | (contributed by brian d foy)
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211 |
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212 | Exuberent ctags supports Perl: http://ctags.sourceforge.net/
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213 |
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214 | You might also try pltags: http://www.mscha.com/pltags.zip
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215 |
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216 | =head2 Is there an IDE or Windows Perl Editor?
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217 |
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218 | Perl programs are just plain text, so any editor will do.
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219 |
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220 | If you're on Unix, you already have an IDE--Unix itself. The UNIX
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221 | philosophy is the philosophy of several small tools that each do one
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222 | thing and do it well. It's like a carpenter's toolbox.
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223 |
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224 | If you want an IDE, check the following (in alphabetical order, not
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225 | order of preference):
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226 |
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227 | =over 4
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228 |
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229 | =item Eclipse
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230 |
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231 | http://e-p-i-c.sf.net/
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232 |
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233 | The Eclipse Perl Integration Project integrates Perl
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234 | editing/debugging with Eclipse.
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235 |
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236 | =item Enginsite
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237 |
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238 | http://www.enginsite.com/
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239 |
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240 | Perl Editor by EngInSite is a complete integrated development
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241 | environment (IDE) for creating, testing, and debugging Perl scripts;
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242 | the tool runs on Windows 9x/NT/2000/XP or later.
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243 |
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244 | =item Komodo
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245 |
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246 | http://www.ActiveState.com/Products/Komodo/
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247 |
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248 | ActiveState's cross-platform (as of October 2004, that's Windows, Linux,
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249 | and Solaris), multi-language IDE has Perl support, including a regular expression
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250 | debugger and remote debugging.
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251 |
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252 | =item Open Perl IDE
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253 |
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254 | http://open-perl-ide.sourceforge.net/
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255 |
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256 | Open Perl IDE is an integrated development environment for writing
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257 | and debugging Perl scripts with ActiveState's ActivePerl distribution
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258 | under Windows 95/98/NT/2000.
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259 |
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260 | =item OptiPerl
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261 |
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262 | http://www.optiperl.com/
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263 |
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264 | OptiPerl is a Windows IDE with simulated CGI environment, including
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265 | debugger and syntax highlighting editor.
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266 |
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267 | =item PerlBuilder
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268 |
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269 | http://www.solutionsoft.com/perl.htm
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270 |
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271 | PerlBuidler is an integrated development environment for Windows that
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272 | supports Perl development.
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273 |
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274 | =item visiPerl+
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275 |
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276 | http://helpconsulting.net/visiperl/
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277 |
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278 | From Help Consulting, for Windows.
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279 |
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280 | =item Visual Perl
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281 |
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282 | http://www.activestate.com/Products/Visual_Perl/
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283 |
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284 | Visual Perl is a Visual Studio.NET plug-in from ActiveState.
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285 |
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286 | =item Zeus
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287 |
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288 | http://www.zeusedit.com/lookmain.html
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289 |
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290 | Zeus for Window is another Win32 multi-language editor/IDE
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291 | that comes with support for Perl:
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292 |
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293 | =back
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294 |
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295 | For editors: if you're on Unix you probably have vi or a vi clone
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296 | already, and possibly an emacs too, so you may not need to download
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297 | anything. In any emacs the cperl-mode (M-x cperl-mode) gives you
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298 | perhaps the best available Perl editing mode in any editor.
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299 |
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300 | If you are using Windows, you can use any editor that lets you work
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301 | with plain text, such as NotePad or WordPad. Word processors, such as
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302 | Microsoft Word or WordPerfect, typically do not work since they insert
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303 | all sorts of behind-the-scenes information, although some allow you to
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304 | save files as "Text Only". You can also download text editors designed
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305 | specifically for programming, such as Textpad (
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306 | http://www.textpad.com/ ) and UltraEdit ( http://www.ultraedit.com/ ),
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307 | among others.
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308 |
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309 | If you are using MacOS, the same concerns apply. MacPerl (for Classic
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310 | environments) comes with a simple editor. Popular external editors are
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311 | BBEdit ( http://www.bbedit.com/ ) or Alpha (
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312 | http://www.his.com/~jguyer/Alpha/Alpha8.html ). MacOS X users can use
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313 | Unix editors as well. Neil Bowers (the man behind Geekcruises) has a
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314 | list of Mac editors that can handle Perl (
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315 | http://www.neilbowers.org/macperleditors.html ).
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316 |
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317 | =over 4
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318 |
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319 | =item GNU Emacs
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320 |
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321 | http://www.gnu.org/software/emacs/windows/ntemacs.html
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322 |
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323 | =item MicroEMACS
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324 |
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325 | http://www.microemacs.de/
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326 |
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327 | =item XEmacs
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328 |
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329 | http://www.xemacs.org/Download/index.html
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330 |
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331 | =item Jed
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332 |
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333 | http://space.mit.edu/~davis/jed/
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334 |
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335 | =back
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336 |
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337 | or a vi clone such as
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338 |
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339 | =over 4
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340 |
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341 | =item Elvis
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342 |
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343 | ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
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344 |
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345 | =item Vile
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346 |
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347 | http://dickey.his.com/vile/vile.html
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348 |
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349 | =item Vim
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350 |
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351 | http://www.vim.org/
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352 |
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353 | =back
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354 |
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355 | For vi lovers in general, Windows or elsewhere:
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356 |
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357 | http://www.thomer.com/thomer/vi/vi.html
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358 |
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359 | nvi ( http://www.bostic.com/vi/ , available from CPAN in src/misc/) is
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360 | yet another vi clone, unfortunately not available for Windows, but in
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361 | UNIX platforms you might be interested in trying it out, firstly because
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362 | strictly speaking it is not a vi clone, it is the real vi, or the new
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363 | incarnation of it, and secondly because you can embed Perl inside it
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364 | to use Perl as the scripting language. nvi is not alone in this,
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365 | though: at least also vim and vile offer an embedded Perl.
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366 |
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367 | The following are Win32 multilanguage editor/IDESs that support Perl:
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368 |
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369 | =over 4
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370 |
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371 | =item Codewright
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372 |
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373 | http://www.borland.com/codewright/
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374 |
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375 | =item MultiEdit
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376 |
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377 | http://www.MultiEdit.com/
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378 |
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379 | =item SlickEdit
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380 |
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381 | http://www.slickedit.com/
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382 |
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383 | =back
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384 |
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385 | There is also a toyedit Text widget based editor written in Perl
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386 | that is distributed with the Tk module on CPAN. The ptkdb
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387 | ( http://world.std.com/~aep/ptkdb/ ) is a Perl/tk based debugger that
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388 | acts as a development environment of sorts. Perl Composer
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389 | ( http://perlcomposer.sourceforge.net/ ) is an IDE for Perl/Tk
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390 | GUI creation.
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391 |
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392 | In addition to an editor/IDE you might be interested in a more
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393 | powerful shell environment for Win32. Your options include
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394 |
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395 | =over 4
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396 |
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397 | =item Bash
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398 |
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399 | from the Cygwin package ( http://sources.redhat.com/cygwin/ )
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400 |
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401 | =item Ksh
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402 |
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403 | from the MKS Toolkit ( http://www.mks.com/ ), or the Bourne shell of
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404 | the U/WIN environment ( http://www.research.att.com/sw/tools/uwin/ )
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405 |
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406 | =item Tcsh
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407 |
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408 | ftp://ftp.astron.com/pub/tcsh/ , see also
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409 | http://www.primate.wisc.edu/software/csh-tcsh-book/
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410 |
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411 | =item Zsh
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412 |
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413 | ftp://ftp.blarg.net/users/amol/zsh/ , see also http://www.zsh.org/
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414 |
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415 | =back
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416 |
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417 | MKS and U/WIN are commercial (U/WIN is free for educational and
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418 | research purposes), Cygwin is covered by the GNU Public License (but
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419 | that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all
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420 | contain (in addition to the shells) a comprehensive set of standard
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421 | UNIX toolkit utilities.
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422 |
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423 | If you're transferring text files between Unix and Windows using FTP
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424 | be sure to transfer them in ASCII mode so the ends of lines are
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425 | appropriately converted.
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426 |
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427 | On Mac OS the MacPerl Application comes with a simple 32k text editor
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428 | that behaves like a rudimentary IDE. In contrast to the MacPerl Application
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429 | the MPW Perl tool can make use of the MPW Shell itself as an editor (with
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430 | no 32k limit).
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431 |
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432 | =over 4
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433 |
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434 | =item Affrus
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435 |
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436 | is a full Perl development environment with full debugger support
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437 | ( http://www.latenightsw.com ).
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438 |
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439 | =item Alpha
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440 |
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441 | is an editor, written and extensible in Tcl, that nonetheless has
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442 | built in support for several popular markup and programming languages
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443 | including Perl and HTML ( http://www.his.com/~jguyer/Alpha/Alpha8.html ).
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444 |
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445 | =item BBEdit and BBEdit Lite
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446 |
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447 | are text editors for Mac OS that have a Perl sensitivity mode
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448 | ( http://web.barebones.com/ ).
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449 |
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450 |
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451 | =back
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452 |
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453 | Pepper and Pe are programming language sensitive text editors for Mac
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454 | OS X and BeOS respectively ( http://www.hekkelman.com/ ).
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455 |
|
---|
456 | =head2 Where can I get Perl macros for vi?
|
---|
457 |
|
---|
458 | For a complete version of Tom Christiansen's vi configuration file,
|
---|
459 | see http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
|
---|
460 | the standard benchmark file for vi emulators. The file runs best with nvi,
|
---|
461 | the current version of vi out of Berkeley, which incidentally can be built
|
---|
462 | with an embedded Perl interpreter--see http://www.cpan.org/src/misc/ .
|
---|
463 |
|
---|
464 | =head2 Where can I get perl-mode for emacs?
|
---|
465 |
|
---|
466 | Since Emacs version 19 patchlevel 22 or so, there have been both a
|
---|
467 | perl-mode.el and support for the Perl debugger built in. These should
|
---|
468 | come with the standard Emacs 19 distribution.
|
---|
469 |
|
---|
470 | In the Perl source directory, you'll find a directory called "emacs",
|
---|
471 | which contains a cperl-mode that color-codes keywords, provides
|
---|
472 | context-sensitive help, and other nifty things.
|
---|
473 |
|
---|
474 | Note that the perl-mode of emacs will have fits with C<"main'foo">
|
---|
475 | (single quote), and mess up the indentation and highlighting. You
|
---|
476 | are probably using C<"main::foo"> in new Perl code anyway, so this
|
---|
477 | shouldn't be an issue.
|
---|
478 |
|
---|
479 | =head2 How can I use curses with Perl?
|
---|
480 |
|
---|
481 | The Curses module from CPAN provides a dynamically loadable object
|
---|
482 | module interface to a curses library. A small demo can be found at the
|
---|
483 | directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep.gz ;
|
---|
484 | this program repeats a command and updates the screen as needed, rendering
|
---|
485 | B<rep ps axu> similar to B<top>.
|
---|
486 |
|
---|
487 | =head2 How can I use X or Tk with Perl?
|
---|
488 |
|
---|
489 | Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
|
---|
490 | that doesn't force you to use Tcl just to get at Tk. Sx is an interface
|
---|
491 | to the Athena Widget set. Both are available from CPAN. See the
|
---|
492 | directory http://www.cpan.org/modules/by-category/08_User_Interfaces/
|
---|
493 |
|
---|
494 | Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
|
---|
495 | http://phaseit.net/claird/comp.lang.perl.tk/ptkFAQ.html , the Perl/Tk Reference
|
---|
496 | Guide available at
|
---|
497 | http://www.cpan.org/authors/Stephen_O_Lidie/ , and the
|
---|
498 | online manpages at
|
---|
499 | http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
|
---|
500 |
|
---|
501 | =head2 How can I make my Perl program run faster?
|
---|
502 |
|
---|
503 | The best way to do this is to come up with a better algorithm. This
|
---|
504 | can often make a dramatic difference. Jon Bentley's book
|
---|
505 | I<Programming Pearls> (that's not a misspelling!) has some good tips
|
---|
506 | on optimization, too. Advice on benchmarking boils down to: benchmark
|
---|
507 | and profile to make sure you're optimizing the right part, look for
|
---|
508 | better algorithms instead of microtuning your code, and when all else
|
---|
509 | fails consider just buying faster hardware. You will probably want to
|
---|
510 | read the answer to the earlier question "How do I profile my Perl
|
---|
511 | programs?" if you haven't done so already.
|
---|
512 |
|
---|
513 | A different approach is to autoload seldom-used Perl code. See the
|
---|
514 | AutoSplit and AutoLoader modules in the standard distribution for
|
---|
515 | that. Or you could locate the bottleneck and think about writing just
|
---|
516 | that part in C, the way we used to take bottlenecks in C code and
|
---|
517 | write them in assembler. Similar to rewriting in C, modules that have
|
---|
518 | critical sections can be written in C (for instance, the PDL module
|
---|
519 | from CPAN).
|
---|
520 |
|
---|
521 | If you're currently linking your perl executable to a shared
|
---|
522 | I<libc.so>, you can often gain a 10-25% performance benefit by
|
---|
523 | rebuilding it to link with a static libc.a instead. This will make a
|
---|
524 | bigger perl executable, but your Perl programs (and programmers) may
|
---|
525 | thank you for it. See the F<INSTALL> file in the source distribution
|
---|
526 | for more information.
|
---|
527 |
|
---|
528 | The undump program was an ancient attempt to speed up Perl program by
|
---|
529 | storing the already-compiled form to disk. This is no longer a viable
|
---|
530 | option, as it only worked on a few architectures, and wasn't a good
|
---|
531 | solution anyway.
|
---|
532 |
|
---|
533 | =head2 How can I make my Perl program take less memory?
|
---|
534 |
|
---|
535 | When it comes to time-space tradeoffs, Perl nearly always prefers to
|
---|
536 | throw memory at a problem. Scalars in Perl use more memory than
|
---|
537 | strings in C, arrays take more than that, and hashes use even more. While
|
---|
538 | there's still a lot to be done, recent releases have been addressing
|
---|
539 | these issues. For example, as of 5.004, duplicate hash keys are
|
---|
540 | shared amongst all hashes using them, so require no reallocation.
|
---|
541 |
|
---|
542 | In some cases, using substr() or vec() to simulate arrays can be
|
---|
543 | highly beneficial. For example, an array of a thousand booleans will
|
---|
544 | take at least 20,000 bytes of space, but it can be turned into one
|
---|
545 | 125-byte bit vector--a considerable memory savings. The standard
|
---|
546 | Tie::SubstrHash module can also help for certain types of data
|
---|
547 | structure. If you're working with specialist data structures
|
---|
548 | (matrices, for instance) modules that implement these in C may use
|
---|
549 | less memory than equivalent Perl modules.
|
---|
550 |
|
---|
551 | Another thing to try is learning whether your Perl was compiled with
|
---|
552 | the system malloc or with Perl's builtin malloc. Whichever one it
|
---|
553 | is, try using the other one and see whether this makes a difference.
|
---|
554 | Information about malloc is in the F<INSTALL> file in the source
|
---|
555 | distribution. You can find out whether you are using perl's malloc by
|
---|
556 | typing C<perl -V:usemymalloc>.
|
---|
557 |
|
---|
558 | Of course, the best way to save memory is to not do anything to waste
|
---|
559 | it in the first place. Good programming practices can go a long way
|
---|
560 | toward this:
|
---|
561 |
|
---|
562 | =over 4
|
---|
563 |
|
---|
564 | =item * Don't slurp!
|
---|
565 |
|
---|
566 | Don't read an entire file into memory if you can process it line
|
---|
567 | by line. Or more concretely, use a loop like this:
|
---|
568 |
|
---|
569 | #
|
---|
570 | # Good Idea
|
---|
571 | #
|
---|
572 | while (<FILE>) {
|
---|
573 | # ...
|
---|
574 | }
|
---|
575 |
|
---|
576 | instead of this:
|
---|
577 |
|
---|
578 | #
|
---|
579 | # Bad Idea
|
---|
580 | #
|
---|
581 | @data = <FILE>;
|
---|
582 | foreach (@data) {
|
---|
583 | # ...
|
---|
584 | }
|
---|
585 |
|
---|
586 | When the files you're processing are small, it doesn't much matter which
|
---|
587 | way you do it, but it makes a huge difference when they start getting
|
---|
588 | larger.
|
---|
589 |
|
---|
590 | =item * Use map and grep selectively
|
---|
591 |
|
---|
592 | Remember that both map and grep expect a LIST argument, so doing this:
|
---|
593 |
|
---|
594 | @wanted = grep {/pattern/} <FILE>;
|
---|
595 |
|
---|
596 | will cause the entire file to be slurped. For large files, it's better
|
---|
597 | to loop:
|
---|
598 |
|
---|
599 | while (<FILE>) {
|
---|
600 | push(@wanted, $_) if /pattern/;
|
---|
601 | }
|
---|
602 |
|
---|
603 | =item * Avoid unnecessary quotes and stringification
|
---|
604 |
|
---|
605 | Don't quote large strings unless absolutely necessary:
|
---|
606 |
|
---|
607 | my $copy = "$large_string";
|
---|
608 |
|
---|
609 | makes 2 copies of $large_string (one for $copy and another for the
|
---|
610 | quotes), whereas
|
---|
611 |
|
---|
612 | my $copy = $large_string;
|
---|
613 |
|
---|
614 | only makes one copy.
|
---|
615 |
|
---|
616 | Ditto for stringifying large arrays:
|
---|
617 |
|
---|
618 | {
|
---|
619 | local $, = "\n";
|
---|
620 | print @big_array;
|
---|
621 | }
|
---|
622 |
|
---|
623 | is much more memory-efficient than either
|
---|
624 |
|
---|
625 | print join "\n", @big_array;
|
---|
626 |
|
---|
627 | or
|
---|
628 |
|
---|
629 | {
|
---|
630 | local $" = "\n";
|
---|
631 | print "@big_array";
|
---|
632 | }
|
---|
633 |
|
---|
634 |
|
---|
635 | =item * Pass by reference
|
---|
636 |
|
---|
637 | Pass arrays and hashes by reference, not by value. For one thing, it's
|
---|
638 | the only way to pass multiple lists or hashes (or both) in a single
|
---|
639 | call/return. It also avoids creating a copy of all the contents. This
|
---|
640 | requires some judgment, however, because any changes will be propagated
|
---|
641 | back to the original data. If you really want to mangle (er, modify) a
|
---|
642 | copy, you'll have to sacrifice the memory needed to make one.
|
---|
643 |
|
---|
644 | =item * Tie large variables to disk.
|
---|
645 |
|
---|
646 | For "big" data stores (i.e. ones that exceed available memory) consider
|
---|
647 | using one of the DB modules to store it on disk instead of in RAM. This
|
---|
648 | will incur a penalty in access time, but that's probably better than
|
---|
649 | causing your hard disk to thrash due to massive swapping.
|
---|
650 |
|
---|
651 | =back
|
---|
652 |
|
---|
653 | =head2 Is it safe to return a reference to local or lexical data?
|
---|
654 |
|
---|
655 | Yes. Perl's garbage collection system takes care of this so
|
---|
656 | everything works out right.
|
---|
657 |
|
---|
658 | sub makeone {
|
---|
659 | my @a = ( 1 .. 10 );
|
---|
660 | return \@a;
|
---|
661 | }
|
---|
662 |
|
---|
663 | for ( 1 .. 10 ) {
|
---|
664 | push @many, makeone();
|
---|
665 | }
|
---|
666 |
|
---|
667 | print $many[4][5], "\n";
|
---|
668 |
|
---|
669 | print "@many\n";
|
---|
670 |
|
---|
671 | =head2 How can I free an array or hash so my program shrinks?
|
---|
672 |
|
---|
673 | (contributed by Michael Carman)
|
---|
674 |
|
---|
675 | You usually can't. Memory allocated to lexicals (i.e. my() variables)
|
---|
676 | cannot be reclaimed or reused even if they go out of scope. It is
|
---|
677 | reserved in case the variables come back into scope. Memory allocated
|
---|
678 | to global variables can be reused (within your program) by using
|
---|
679 | undef()ing and/or delete().
|
---|
680 |
|
---|
681 | On most operating systems, memory allocated to a program can never be
|
---|
682 | returned to the system. That's why long-running programs sometimes re-
|
---|
683 | exec themselves. Some operating systems (notably, systems that use
|
---|
684 | mmap(2) for allocating large chunks of memory) can reclaim memory that
|
---|
685 | is no longer used, but on such systems, perl must be configured and
|
---|
686 | compiled to use the OS's malloc, not perl's.
|
---|
687 |
|
---|
688 | In general, memory allocation and de-allocation isn't something you can
|
---|
689 | or should be worrying about much in Perl.
|
---|
690 |
|
---|
691 | See also "How can I make my Perl program take less memory?"
|
---|
692 |
|
---|
693 | =head2 How can I make my CGI script more efficient?
|
---|
694 |
|
---|
695 | Beyond the normal measures described to make general Perl programs
|
---|
696 | faster or smaller, a CGI program has additional issues. It may be run
|
---|
697 | several times per second. Given that each time it runs it will need
|
---|
698 | to be re-compiled and will often allocate a megabyte or more of system
|
---|
699 | memory, this can be a killer. Compiling into C B<isn't going to help
|
---|
700 | you> because the process start-up overhead is where the bottleneck is.
|
---|
701 |
|
---|
702 | There are two popular ways to avoid this overhead. One solution
|
---|
703 | involves running the Apache HTTP server (available from
|
---|
704 | http://www.apache.org/ ) with either of the mod_perl or mod_fastcgi
|
---|
705 | plugin modules.
|
---|
706 |
|
---|
707 | With mod_perl and the Apache::Registry module (distributed with
|
---|
708 | mod_perl), httpd will run with an embedded Perl interpreter which
|
---|
709 | pre-compiles your script and then executes it within the same address
|
---|
710 | space without forking. The Apache extension also gives Perl access to
|
---|
711 | the internal server API, so modules written in Perl can do just about
|
---|
712 | anything a module written in C can. For more on mod_perl, see
|
---|
713 | http://perl.apache.org/
|
---|
714 |
|
---|
715 | With the FCGI module (from CPAN) and the mod_fastcgi
|
---|
716 | module (available from http://www.fastcgi.com/ ) each of your Perl
|
---|
717 | programs becomes a permanent CGI daemon process.
|
---|
718 |
|
---|
719 | Both of these solutions can have far-reaching effects on your system
|
---|
720 | and on the way you write your CGI programs, so investigate them with
|
---|
721 | care.
|
---|
722 |
|
---|
723 | See http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
|
---|
724 |
|
---|
725 | =head2 How can I hide the source for my Perl program?
|
---|
726 |
|
---|
727 | Delete it. :-) Seriously, there are a number of (mostly
|
---|
728 | unsatisfactory) solutions with varying levels of "security".
|
---|
729 |
|
---|
730 | First of all, however, you I<can't> take away read permission, because
|
---|
731 | the source code has to be readable in order to be compiled and
|
---|
732 | interpreted. (That doesn't mean that a CGI script's source is
|
---|
733 | readable by people on the web, though--only by people with access to
|
---|
734 | the filesystem.) So you have to leave the permissions at the socially
|
---|
735 | friendly 0755 level.
|
---|
736 |
|
---|
737 | Some people regard this as a security problem. If your program does
|
---|
738 | insecure things and relies on people not knowing how to exploit those
|
---|
739 | insecurities, it is not secure. It is often possible for someone to
|
---|
740 | determine the insecure things and exploit them without viewing the
|
---|
741 | source. Security through obscurity, the name for hiding your bugs
|
---|
742 | instead of fixing them, is little security indeed.
|
---|
743 |
|
---|
744 | You can try using encryption via source filters (Starting from Perl
|
---|
745 | 5.8 the Filter::Simple and Filter::Util::Call modules are included in
|
---|
746 | the standard distribution), but any decent programmer will be able to
|
---|
747 | decrypt it. You can try using the byte code compiler and interpreter
|
---|
748 | described below, but the curious might still be able to de-compile it.
|
---|
749 | You can try using the native-code compiler described below, but
|
---|
750 | crackers might be able to disassemble it. These pose varying degrees
|
---|
751 | of difficulty to people wanting to get at your code, but none can
|
---|
752 | definitively conceal it (true of every language, not just Perl).
|
---|
753 |
|
---|
754 | It is very easy to recover the source of Perl programs. You simply
|
---|
755 | feed the program to the perl interpreter and use the modules in
|
---|
756 | the B:: hierarchy. The B::Deparse module should be able to
|
---|
757 | defeat most attempts to hide source. Again, this is not
|
---|
758 | unique to Perl.
|
---|
759 |
|
---|
760 | If you're concerned about people profiting from your code, then the
|
---|
761 | bottom line is that nothing but a restrictive license will give you
|
---|
762 | legal security. License your software and pepper it with threatening
|
---|
763 | statements like "This is unpublished proprietary software of XYZ Corp.
|
---|
764 | Your access to it does not give you permission to use it blah blah
|
---|
765 | blah." We are not lawyers, of course, so you should see a lawyer if
|
---|
766 | you want to be sure your license's wording will stand up in court.
|
---|
767 |
|
---|
768 | =head2 How can I compile my Perl program into byte code or C?
|
---|
769 |
|
---|
770 | (contributed by brian d foy)
|
---|
771 |
|
---|
772 | In general, you can't do this. There are some things that may work
|
---|
773 | for your situation though. People usually ask this question
|
---|
774 | because they want to distribute their works without giving away
|
---|
775 | the source code, and most solutions trade disk space for convenience.
|
---|
776 | You probably won't see much of a speed increase either, since most
|
---|
777 | solutions simply bundle a Perl interpreter in the final product
|
---|
778 | (but see L<How can I make my Perl program run faster?>).
|
---|
779 |
|
---|
780 | The Perl Archive Toolkit ( http://par.perl.org/index.cgi ) is Perl's
|
---|
781 | analog to Java's JAR. It's freely available and on CPAN (
|
---|
782 | http://search.cpan.org/dist/PAR/ ).
|
---|
783 |
|
---|
784 | The B::* namespace, often called "the Perl compiler", but is really a way
|
---|
785 | for Perl programs to peek at its innards rather than create pre-compiled
|
---|
786 | versions of your program. However. the B::Bytecode module can turn your
|
---|
787 | script into a bytecode format that could be loaded later by the
|
---|
788 | ByteLoader module and executed as a regular Perl script.
|
---|
789 |
|
---|
790 | There are also some commercial products that may work for you, although
|
---|
791 | you have to buy a license for them.
|
---|
792 |
|
---|
793 | The Perl Dev Kit ( http://www.activestate.com/Products/Perl_Dev_Kit/ )
|
---|
794 | from ActiveState can "Turn your Perl programs into ready-to-run
|
---|
795 | executables for HP-UX, Linux, Solaris and Windows."
|
---|
796 |
|
---|
797 | Perl2Exe ( http://www.indigostar.com/perl2exe.htm ) is a command line
|
---|
798 | program for converting perl scripts to executable files. It targets both
|
---|
799 | Windows and unix platforms.
|
---|
800 |
|
---|
801 | =head2 How can I compile Perl into Java?
|
---|
802 |
|
---|
803 | You can also integrate Java and Perl with the
|
---|
804 | Perl Resource Kit from O'Reilly Media. See
|
---|
805 | http://www.oreilly.com/catalog/prkunix/ .
|
---|
806 |
|
---|
807 | Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in
|
---|
808 | development, allows Perl code to be called from Java. See jpl/README
|
---|
809 | in the Perl source tree.
|
---|
810 |
|
---|
811 | =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
|
---|
812 |
|
---|
813 | For OS/2 just use
|
---|
814 |
|
---|
815 | extproc perl -S -your_switches
|
---|
816 |
|
---|
817 | as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
|
---|
818 | "extproc" handling). For DOS one should first invent a corresponding
|
---|
819 | batch file and codify it in C<ALTERNATE_SHEBANG> (see the
|
---|
820 | F<dosish.h> file in the source distribution for more information).
|
---|
821 |
|
---|
822 | The Win95/NT installation, when using the ActiveState port of Perl,
|
---|
823 | will modify the Registry to associate the C<.pl> extension with the
|
---|
824 | perl interpreter. If you install another port, perhaps even building
|
---|
825 | your own Win95/NT Perl from the standard sources by using a Windows port
|
---|
826 | of gcc (e.g., with cygwin or mingw32), then you'll have to modify
|
---|
827 | the Registry yourself. In addition to associating C<.pl> with the
|
---|
828 | interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
|
---|
829 | run the program C<install-linux.pl> merely by typing C<install-linux>.
|
---|
830 |
|
---|
831 | Under "Classic" MacOS, a perl program will have the appropriate Creator and
|
---|
832 | Type, so that double-clicking them will invoke the MacPerl application.
|
---|
833 | Under Mac OS X, clickable apps can be made from any C<#!> script using Wil
|
---|
834 | Sanchez' DropScript utility: http://www.wsanchez.net/software/ .
|
---|
835 |
|
---|
836 | I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
|
---|
837 | throw the perl interpreter into your cgi-bin directory, in order to
|
---|
838 | get your programs working for a web server. This is an EXTREMELY big
|
---|
839 | security risk. Take the time to figure out how to do it correctly.
|
---|
840 |
|
---|
841 | =head2 Can I write useful Perl programs on the command line?
|
---|
842 |
|
---|
843 | Yes. Read L<perlrun> for more information. Some examples follow.
|
---|
844 | (These assume standard Unix shell quoting rules.)
|
---|
845 |
|
---|
846 | # sum first and last fields
|
---|
847 | perl -lane 'print $F[0] + $F[-1]' *
|
---|
848 |
|
---|
849 | # identify text files
|
---|
850 | perl -le 'for(@ARGV) {print if -f && -T _}' *
|
---|
851 |
|
---|
852 | # remove (most) comments from C program
|
---|
853 | perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
|
---|
854 |
|
---|
855 | # make file a month younger than today, defeating reaper daemons
|
---|
856 | perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
|
---|
857 |
|
---|
858 | # find first unused uid
|
---|
859 | perl -le '$i++ while getpwuid($i); print $i'
|
---|
860 |
|
---|
861 | # display reasonable manpath
|
---|
862 | echo $PATH | perl -nl -072 -e '
|
---|
863 | s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
|
---|
864 |
|
---|
865 | OK, the last one was actually an Obfuscated Perl Contest entry. :-)
|
---|
866 |
|
---|
867 | =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
|
---|
868 |
|
---|
869 | The problem is usually that the command interpreters on those systems
|
---|
870 | have rather different ideas about quoting than the Unix shells under
|
---|
871 | which the one-liners were created. On some systems, you may have to
|
---|
872 | change single-quotes to double ones, which you must I<NOT> do on Unix
|
---|
873 | or Plan9 systems. You might also have to change a single % to a %%.
|
---|
874 |
|
---|
875 | For example:
|
---|
876 |
|
---|
877 | # Unix
|
---|
878 | perl -e 'print "Hello world\n"'
|
---|
879 |
|
---|
880 | # DOS, etc.
|
---|
881 | perl -e "print \"Hello world\n\""
|
---|
882 |
|
---|
883 | # Mac
|
---|
884 | print "Hello world\n"
|
---|
885 | (then Run "Myscript" or Shift-Command-R)
|
---|
886 |
|
---|
887 | # MPW
|
---|
888 | perl -e 'print "Hello world\n"'
|
---|
889 |
|
---|
890 | # VMS
|
---|
891 | perl -e "print ""Hello world\n"""
|
---|
892 |
|
---|
893 | The problem is that none of these examples are reliable: they depend on the
|
---|
894 | command interpreter. Under Unix, the first two often work. Under DOS,
|
---|
895 | it's entirely possible that neither works. If 4DOS was the command shell,
|
---|
896 | you'd probably have better luck like this:
|
---|
897 |
|
---|
898 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
|
---|
899 |
|
---|
900 | Under the Mac, it depends which environment you are using. The MacPerl
|
---|
901 | shell, or MPW, is much like Unix shells in its support for several
|
---|
902 | quoting variants, except that it makes free use of the Mac's non-ASCII
|
---|
903 | characters as control characters.
|
---|
904 |
|
---|
905 | Using qq(), q(), and qx(), instead of "double quotes", 'single
|
---|
906 | quotes', and `backticks`, may make one-liners easier to write.
|
---|
907 |
|
---|
908 | There is no general solution to all of this. It is a mess.
|
---|
909 |
|
---|
910 | [Some of this answer was contributed by Kenneth Albanowski.]
|
---|
911 |
|
---|
912 | =head2 Where can I learn about CGI or Web programming in Perl?
|
---|
913 |
|
---|
914 | For modules, get the CGI or LWP modules from CPAN. For textbooks,
|
---|
915 | see the two especially dedicated to web stuff in the question on
|
---|
916 | books. For problems and questions related to the web, like "Why
|
---|
917 | do I get 500 Errors" or "Why doesn't it run from the browser right
|
---|
918 | when it runs fine on the command line", see the troubleshooting
|
---|
919 | guides and references in L<perlfaq9> or in the CGI MetaFAQ:
|
---|
920 |
|
---|
921 | http://www.perl.org/CGI_MetaFAQ.html
|
---|
922 |
|
---|
923 | =head2 Where can I learn about object-oriented Perl programming?
|
---|
924 |
|
---|
925 | A good place to start is L<perltoot>, and you can use L<perlobj>,
|
---|
926 | L<perlboot>, L<perltoot>, L<perltooc>, and L<perlbot> for reference.
|
---|
927 |
|
---|
928 | A good book on OO on Perl is the "Object-Oriented Perl"
|
---|
929 | by Damian Conway from Manning Publications, or "Learning Perl
|
---|
930 | References, Objects, & Modules" by Randal Schwartz and Tom
|
---|
931 | Phoenix from O'Reilly Media.
|
---|
932 |
|
---|
933 | =head2 Where can I learn about linking C with Perl?
|
---|
934 |
|
---|
935 | If you want to call C from Perl, start with L<perlxstut>,
|
---|
936 | moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
|
---|
937 | call Perl from C, then read L<perlembed>, L<perlcall>, and
|
---|
938 | L<perlguts>. Don't forget that you can learn a lot from looking at
|
---|
939 | how the authors of existing extension modules wrote their code and
|
---|
940 | solved their problems.
|
---|
941 |
|
---|
942 | You might not need all the power of XS. The Inline::C module lets
|
---|
943 | you put C code directly in your Perl source. It handles all the
|
---|
944 | magic to make it work. You still have to learn at least some of
|
---|
945 | the perl API but you won't have to deal with the complexity of the
|
---|
946 | XS support files.
|
---|
947 |
|
---|
948 | =head2 I've read perlembed, perlguts, etc., but I can't embed perl in my C program; what am I doing wrong?
|
---|
949 |
|
---|
950 | Download the ExtUtils::Embed kit from CPAN and run `make test'. If
|
---|
951 | the tests pass, read the pods again and again and again. If they
|
---|
952 | fail, see L<perlbug> and send a bug report with the output of
|
---|
953 | C<make test TEST_VERBOSE=1> along with C<perl -V>.
|
---|
954 |
|
---|
955 | =head2 When I tried to run my script, I got this message. What does it mean?
|
---|
956 |
|
---|
957 | A complete list of Perl's error messages and warnings with explanatory
|
---|
958 | text can be found in L<perldiag>. You can also use the splain program
|
---|
959 | (distributed with Perl) to explain the error messages:
|
---|
960 |
|
---|
961 | perl program 2>diag.out
|
---|
962 | splain [-v] [-p] diag.out
|
---|
963 |
|
---|
964 | or change your program to explain the messages for you:
|
---|
965 |
|
---|
966 | use diagnostics;
|
---|
967 |
|
---|
968 | or
|
---|
969 |
|
---|
970 | use diagnostics -verbose;
|
---|
971 |
|
---|
972 | =head2 What's MakeMaker?
|
---|
973 |
|
---|
974 | This module (part of the standard Perl distribution) is designed to
|
---|
975 | write a Makefile for an extension module from a Makefile.PL. For more
|
---|
976 | information, see L<ExtUtils::MakeMaker>.
|
---|
977 |
|
---|
978 | =head1 AUTHOR AND COPYRIGHT
|
---|
979 |
|
---|
980 | Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and
|
---|
981 | other authors as noted. All rights reserved.
|
---|
982 |
|
---|
983 | This documentation is free; you can redistribute it and/or modify it
|
---|
984 | under the same terms as Perl itself.
|
---|
985 |
|
---|
986 | Irrespective of its distribution, all code examples here are in the public
|
---|
987 | domain. You are permitted and encouraged to use this code and any
|
---|
988 | derivatives thereof in your own programs for fun or for profit as you
|
---|
989 | see fit. A simple comment in the code giving credit to the FAQ would
|
---|
990 | be courteous but is not required.
|
---|