in reply to opening file for editing

For a quick file update, perl -pi -e "s/e/\*\*/ig" D:\RAM\perl\test should work. If your needs are more complex, see open, in particular the '+<' and '+>' bits.

update - changed single to double quotes around the s///ig after belatedly realizing the significance of D:

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Re^2: opening file for editing
by ramprasad27 (Sexton) on Oct 09, 2011 at 08:10 UTC
    I wont be able to do it using perl one liner what i want is open an already existing file search for a pattern replace it with something else on the fly i dont want any temp files to be created
[reply]
      Just For Fun: ... to update a file "in place". 
      ...
    open(my $READER,'+<',$Filename_S)
        or die "Can't open '$Filename_S'! $!";
    open(my $WRITER,'+<',$Filename_S)                      # Don't use
+ '+>'
        or die "Can't open '$Filename_S'! $!";
    # The overflow buffer:
    my @Buffer_a;
    while (<$READER>) {
        # Read (past tense) a line - buffer its replacement ...

        # Modify the line here!
        my $Update_s=...
         
        push(@Buffer_a,$Update_s);
        # Write from the overflow buffer if we can ...
        while (@Buffer_a && length($Buffer_a[0]) < tell($READER)-tell(
+$WRITER)) {
            # Enough room to write $Buffer_a[0] so write it ...
            print $WRITER shift(@Buffer_a);
             };
         };
    # Nothing more to read ...
    close($READER)
        or die "Can't close '$Filename_S'! $!";
    # If there's anything in the buffer write it ...
    while (@Buffer_a) {
        print $WRITER shift(@Buffer_a);
         };
    # Truncate the file, in case, what we're writing is shorter than w
+hat we read
    truncate($WRITER,tell($WRITER));
    #  ... and close
    close($WRITER)
        or die "Can't close '$Filename_S'! $!";
...

      [download]
      Be aware that if something should happen during the update one may be "up the creek without a paddle".
[reply]
[d/l]

      you can do this in two steps:

      read open
dump all to a variable (in memory)
apply a substitution to this variable
close
re-open the file, now for writing
print the changed variable to the file (overwrite the whole file)
and close again

      [download]

      No temp files here, and your file is updated as you want. Use perldoc for the details.

[reply]
[d/l]
        oh well, this seems to be more straightforward solution, thats fine..but can this be done by opening file only once
[reply]
      Then you'll have to switch to Microsoft Word ™.
[reply]
        so its not possible using perl
[reply]

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