GrandFather has asked for the wisdom of the Perl Monks concerning the following question:

Ok, I have <> and $^I down pat for inplace file edit where files are passed on the command line. Is there a neat way of doing the same for <filehandle> rather than something like this:

my $SomeFile = "delme.txt";

open inFile, "<$SomeFile" or die "Can't open $SomeFile for input: $!";
open outFile, ">~$SomeFile" or die "Can't open ~$SomeFile for output: 
+$!";

print outFile while <inFile>;

close inFile;
close outFile;

unlink "$SomeFile.bak";
rename $SomeFile, "$SomeFile.bak";
rename "~$SomeFile", $SomeFile;

[download]
Perl is Huffman encoded by design.

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Re: Inplace file edit mark II
by kaif (Friar) on Jun 09, 2005 at 23:59 UTC
    Please see perlfaq5: 
           How can I use Perl's "-i" option from within a program?

       "-i" sets the value of Perl's $^I variable, which in turn affec
+ts the behavior of "<>"; see perlrun for more details.  By modifying 
+the appropriate variables
       directly, you can get the same behavior within a larger program
+.  For example:

            # ...
            {
               local($^I, @ARGV) = ('.orig', glob("*.c"));
               while (<>) {
                  if ($. == 1) {
                      print "This line should appear at the top of eac
+h file\n";
                  }
                  s/\b(p)earl\b/${1}erl/i;        # Correct typos, pre
+serving case
                  print;
                  close ARGV if eof;              # Reset $.
               }
            }
            # $^I and @ARGV return to their old values here

       This block modifies all the ".c" files in the current directory
+, leaving a backup of the original data from each file in a new ".c.o
+rig" file.

    [download]

    That is one approach, using <> by setting @ARGV. If you simply wish to work on another filehandle, look at the first question in perlfaq5 ("How do I flush/unbuffer an output filehandle? Why must I do this?"), where it states how to set per-filehandle variables (like $| and our desired variable $^I): 

    # Long, understandable version
$old_fh = select(OUTPUT_HANDLE);
$^I = '.orig';
select($old_fh);

# Short version
$^I = '.orig', select $_ for select OUTPUT_HANDLE;

    [download]
    or if you wish to keep the new OUTPUT_HANDLE selected, simply select( OUTPUT_HANDLE ); $^I = '.orig'; Good luck!

    Update: Trying to actually answer the question.
[reply]
[d/l]
[select]

      Yep, that's what I wanted.

      You would think that in the few weeks I've been learning Perl that I wouldn't have time to forget stuff like that. I know I read it in the Camel or the Lama, but I hadn't used it and - poof - gone. :-(

      So the solution I was after is like this:

      local($^I, @ARGV) = ('.bak', 'delme.txt');
print outFile while <>;

      [download]
      Perl is Huffman encoded by design.
[reply]
[d/l]

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