cvs commit: perlfaq perlfaq5.pod

cvsuser     02/03/11 14:25:26

  Modified:    .        perlfaq5.pod
  Log:
  * sync with sources from perl5.7.3
  
  * removed long answer to 'How do I change one line in a file' and
  replaced it with a reference to the Tie::File module.
  
  Revision  Changes    Path
  1.12      +3 -78     perlfaq/perlfaq5.pod
  
  Index: perlfaq5.pod
  ===================================================================
  RCS file: /cvs/public/perlfaq/perlfaq5.pod,v
  retrieving revision 1.11
  retrieving revision 1.12
  diff -u -w -r1.11 -r1.12
  --- perlfaq5.pod	11 Mar 2002 21:54:57 -0000	1.11
  +++ perlfaq5.pod	11 Mar 2002 22:25:25 -0000	1.12
  @@ -1,6 +1,6 @@
   =head1 NAME
   
  -perlfaq5 - Files and Formats ($Revision: 1.11 $, $Date: 2002/03/11 21:54:57 $)
  +perlfaq5 - Files and Formats ($Revision: 1.12 $, $Date: 2002/03/11 22:25:25 $)
   
   =head1 DESCRIPTION
   
  @@ -78,83 +78,8 @@
   
   =head2 How do I change one line in a file/delete a line in a file/insert a line in the middle of a file/append to the beginning of a file?
   
  -Those are operations of a text editor.  Perl is not a text editor.
  -Perl is a programming language.  You have to decompose the problem into
  -low-level calls to read, write, open, close, and seek.
  -
  -Although humans have an easy time thinking of a text file as being a
  -sequence of lines that operates much like a stack of playing cards--or
  -punch cards--computers usually see the text file as a sequence of bytes.
  -In general, there's no direct way for Perl to seek to a particular line
  -of a file, insert text into a file, or remove text from a file.
  -
  -(There are exceptions in special circumstances.  You can add or remove
  -data at the very end of the file.  A sequence of bytes can be replaced
  -with another sequence of the same length.  The C<$DB_RECNO> array
  -bindings as documented in L<DB_File> also provide a direct way of
  -modifying a file.  Files where all lines are the same length are also
  -easy to alter.)
  -
  -The general solution is to create a temporary copy of the text file with
  -the changes you want, then copy that over the original.  This assumes
  -no locking.
  -
  -    $old = $file;
  -    $new = "$file.tmp.$$";
  -    $bak = "$file.orig";
  -
  -    open(OLD, "< $old") 	or die "can't open $old: $!";
  -    open(NEW, "> $new") 	or die "can't open $new: $!";
  -
  -    # Correct typos, preserving case
  -    while (<OLD>) {
  -	s/\b(p)earl\b/${1}erl/i;
  -	(print NEW $_)		or die "can't write to $new: $!";
  -    }
  -
  -    close(OLD)			or die "can't close $old: $!";
  -    close(NEW) 			or die "can't close $new: $!";
  -
  -    rename($old, $bak)		or die "can't rename $old to $bak: $!";
  -    rename($new, $old)		or die "can't rename $new to $old: $!";
  -
  -Perl can do this sort of thing for you automatically with the C<-i>
  -command-line switch or the closely-related C<$^I> variable (see
  -L<perlrun> for more details).  Note that
  -C<-i> may require a suffix on some non-Unix systems; see the
  -platform-specific documentation that came with your port.
  -
  -    # Renumber a series of tests from the command line
  -    perl -pi -e 's/(^\s+test\s+)\d+/ $1 . ++$count /e' t/op/taint.t
  -
  -    # form a script
  -    local($^I, @ARGV) = ('.orig', glob("*.c"));
  -    while (<>) {
  -	if ($. == 1) {
  -	    print "This line should appear at the top of each file\n";
  -	}
  -	s/\b(p)earl\b/${1}erl/i;        # Correct typos, preserving case
  -	print;
  -	close ARGV if eof;              # Reset $.
  -    }
  -
  -If you need to seek to an arbitrary line of a file that changes
  -infrequently, you could build up an index of byte positions of where
  -the line ends are in the file.  If the file is large, an index of
  -every tenth or hundredth line end would allow you to seek and read
  -fairly efficiently.  If the file is sorted, try the look.pl library
  -(part of the standard perl distribution).
  -
  -In the unique case of deleting lines at the end of a file, you
  -can use tell() and truncate().  The following code snippet deletes
  -the last line of a file without making a copy or reading the
  -whole file into memory:
  -
  -	open (FH, "+< $file");
  -        while ( <FH> ) { $addr = tell(FH) unless eof(FH) }
  -        truncate(FH, $addr);
  -
  -Error checking is left as an exercise for the reader.
  +Use the Tie::File module, which is included in the standard
  +distribution since Perl 5.8.0.
   
   =head2 How do I count the number of lines in a file?