Thank you very much Andy, Nathan, Shawn for your kind help.
I am new to the perl. Why auto-flush is needed here (STDERR autoflushes)?
It will free the memory or something else.
Regards,
Jitendra
On Tue, Jul 9, 2013 at 9:10 PM, Andy Bach <afb...@gmail.com> wrote:
>
> On Tue, Jul 9, 2013 at 9:37 AM, Nathan Hilterbrand <noset...@cotse.net>wrote:
>
>> I want to open a file read+write mode and change
>> > the
>> > some content in same file without creating another file and copy to it.
>>
>
>
> You might want to look at the perl "in place mode" [1], so something like
> perl -i.bak -pe ' s/BLR/bangalore/g;' myfile.txt
>
> will modifiy myfile.txt, as in a while loop (via the -p option:
> while (<>) {
> s/BLR/bangalore/g;
> }
>
> ) and, as there a param to the -i option, leave you with the original text
> in a myfile.txt.bak file
>
>
> [1]
> perldoc perlrun has
> -i[extension]
> specifies that files processed by the "<>" construct are to be
> edited in-place. It does this by
> renaming the input file, opening the output file by the
> original name, and selecting that output file
> as the default for print() statements. The extension, if
> supplied, is used to modify the name of the
> old file to make a backup copy, following these rules:
>
> If no extension is supplied, no backup is made and the current
> file is overwritten.
>
> If the extension doesn’t contain a "*", then it is appended to
> the end of the current filename as a
> suffix. If the extension does contain one or more "*"
> characters, then each "*" is replaced with the
> current filename. In Perl terms, you could think of this as:
>
> ($backup = $extension) =~ s/\*/$file_name/g;
>
> This allows you to add a prefix to the backup file, instead of
> (or in addition to) a suffix:
>
> $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to
> 'orig_fileA'
>
> Or even to place backup copies of the original files into
> another directory (provided the directory
> already exists):
>
> $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to
> 'old/fileA.orig'
>
> These sets of one-liners are equivalent:
>
> $ perl -pi -e 's/bar/baz/' fileA # overwrite
> current file
> $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite
> current file
>
> $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to
> 'fileA.orig'
> $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to
> 'fileA.orig'
>
> From the shell, saying
>
> $ perl -p -i.orig -e "s/foo/bar/; ... "
>
> is the same as using the program:
>
> #!/usr/bin/perl -pi.orig
> s/foo/bar/;
>
> which is equivalent to
>
> #!/usr/bin/perl
> $extension = '.orig';
> LINE: while (<>) {
> if ($ARGV ne $oldargv) {
> if ($extension !~ /\*/) {
> $backup = $ARGV . $extension;
> }
> else {
> ($backup = $extension) =~ s/\*/$ARGV/g;
> }
> rename($ARGV, $backup);
> open(ARGVOUT, ">$ARGV");
> select(ARGVOUT);
> $oldargv = $ARGV;
> }
> s/foo/bar/;
> }
> continue {
> print; # this prints to original filename
> }
> select(STDOUT);
>
> except that the -i form doesn’t need to compare $ARGV to
> $oldargv to know when the filename has
> changed. It does, however, use ARGVOUT for the selected
> filehandle. Note that STDOUT is restored as
> the default output filehandle after the loop.
>
> As shown above, Perl creates the backup file whether or not
> any output is actually changed. So this is
> just a fancy way to copy files:
>
> $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
> or
> $ perl -p -i'.orig' -e 1 file1 file2 file3...
> You cannot use -i to create directories or to strip extensions from
> files.
>
> Perl does not expand "~" in filenames, which is good, since
> some folks use it for their backup files:
>
> $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
>
> Note that because -i renames or deletes the original file
> before creating a new file of the same name,
> UNIX-style soft and hard links will not be preserved.
>
> Finally, the -i switch does not impede execution when no files
> are given on the command line. In this
> case, no backup is made (the original file cannot, of course,
> be determined) and processing proceeds
> from STDIN to STDOUT as might be expected.
>
> --
>
> a
>
> Andy Bach,
> afb...@gmail.com
> 608 658-1890 cell
> 608 261-5738 wk
>
