Perl

• How to find if a perl module is installed?
  perl -MMODULENAME -e1
  Eg: perl -MHTML::Embperl -e1 If there is no msg then the module is present
  
  
• How to check the version number of an installed module?
  Assumes the module uses $VERSION, but then, most CPAN modules do)
  perl -MMODULENAME -e'print "$MODULENAME::VERSION\n";'
  For example:
  perl -MHTML::Embperl -e'print "$HTML::Embperl::VERSION\n";'
  
  
• How to determine where a module is installed?
  Lists every dir used by the module, including man pages, etc. Should be entered on one line.
  perl -MExtUtils::Installed -e'$,="\n";print ExtUtils::Installed->new()->directories("MODULENAME")," "'
  For example:
  perl -MExtUtils::Installed
  -e'$,="\n";print ExtUtils::Installed->new()->directories("HTML::Embperl")," "'
  This technique relies on ExtUtils::Installed, which is part of the standard Perl distro these days.
  
  
• Installing things from CPAN?
  $ perl -MCPAN -e shell // Shell appears.
  install DBD::mysql
  
  
• How to including newly installed Perl modules?
  perl -I ...
  
  
• How to create an array of file handles?
  my %fh_hash=();
  if(!exists $fh_hash{$f_name}) {
  local *FILE;
  open(FILE, ">$f_name") || die;
  $fh_hash{$f_name}=*FILE;
  }
  Later to print to the file:
  print {$fh_hash{$f_name}} $_;
  
  
• How to sort one array using the sort order of another array?
  my @sk = @k[sort { $v[$a] <=> $v[$b] } 0 .. $#v];
  Sort the array @k using the same sort order as that of sorting array @v. Use '<=>' for numerical sort order and 'cmp' for lexicographic sort order.
  
  
• Generate random numbers in perl?
  my $range = 100;
  my $random_number = int(rand($range));
  
  
• Obtain difference between two date-time strings?
  use Date::Manip;
  my $err; my $date1=ParseDate("02/Jul/2007:15:06:27");
  my $date2=ParseDate("02/Jul/2007:15:16:27");
  my $diff = DateCalc($date1, $date2, \$err); # Compute $date2-$date1 my $diff_in_mins= Delta_Format($diff, 0, "%mt"); # Difference in minutes.