Re^3: Masters of Loops and Filehandles

[graff]

Well, this is a little bit of progress... (but not much). As far as having a single perl script to do all this instead of a complicated shell command with multiple scripts: treat the various steps as a series of blocks or subroutines so that you put the whole sequence into a single perl script, and nothing else needs to change from the plan that I outlined.

There's still a problem about setting the replacement string for the file updates. Why are you not able to explain this clearly? You start by saying "The replacement pattern can be whatever I want it to be", then you say your "code so far works as far as finding the replacement string which is different in each file because it is a serial number", but the code you posted doesn't really show anything of that sort.

I see you have a variable called "$tapeDev" (which is not declared or given a value in the posted snippet), you are appending to that a counter number that (probably) increments with each file. Is this string supposed to end up being 10 bytes long, and is it supposed to replace the 10 bytes you read from the mysterious (as yet unspecified) fixed offset in each file?

I'll assume "yes" and "yes". Considering the code you just posted, I gather that you didn't really understand what I was saying above, so here's what I described as separate scripts, but implemented as steps in a single script (not tested):

use strict;

# get the list of files to work on:

my $tkdir = ".";   # put a real path here
chdir $tkdir or die "chdir $tkdir: $!\n";  # this makes things easier 
+below

opendir( TKS, "." );
my @files = grep { -f } readdir TKS ; # only keep the things you want 
+here
closedir TKS;

# read 10 bytes at fixed offset in each file, set replacement values:

my %edit_list;
my $counter = 0;
my $fixed_offset = 50;  # put your real byte offset value here

for my $file ( @files ) {
    open( FH, '<', $file ) or do {
        warn " skipped $file: $!\n";
        next;
    };
    binmode FH;
    seek FH, $fixed_offset, 0;
    read FH, $_, 10;
    close FH;
    my $replace = sprintf( "foobar%04d", ++$counter );
    $edit_list{$file} = [ $_, $replace ];
}

# now, go through the files and edit each one

for my $file ( keys %edit_list ) {
    local $/;  # sets input record separator to undef for slurp mode
    open( FH, '<', $file );
    $_ = <FH>;
    close FH;

    s/\Q$edit_list{$file}[0]/$edit_list{$file}[1]/g;

    open( FN, '>', "$file.edited.$$" )   # write to a different name, 
+just to be safe
        or die $!;
    print FN;
    close FN;
}

(Updated to include the "chdir()" step at the top, followed by opendir( TKS, "." ); -- if your previous attempts had anything other than "." as the value for $tkdir, that would have been a big part of your problem -- I see you covered that step in your snippet.)

If that's the sort of thing you're trying to do, it shouldn't be a problem to use the different output file names, at least until you're confident that it really is doing the right thing. Then you can change the last open statement so that it uses each original file name (replacing the contents of the original files).