Loop Through Files and Update Headers

jalopez453 has asked for the wisdom of the Perl Monks concerning the following question:

I have a script where I am looping through all files in the folder and I am wanting to update the headers. The issue I am having is, it is looping through all the files and appending the new header but it is not copying down the remaining data in each file, it is only pasting the header. Can someone take a look at my code and tell me what is missing to append the remaining data in my files and not just the header.

use strict;
use warnings;
use Tie::File;

opendir IN, 'Output'; # name of folder where files are
my @in = grep { /\.txt$/ } readdir IN; # read all files in dir
closedir IN;

for my $in (@in) {
open IN, '<', "Output/$in" || next;

tie my @array, 'Tie::File', $in or die "Could not open file '$in' $!";
$array[0] = 'Header1, Header2, Header3, etc etc.';
untie @array;
}
[download]

Comment on Loop Through Files and Update Headers Download Code

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Re: Loop Through Files and Update Headers by choroba (Cardinal) on Mar 05, 2020 at 22:54 UTC
Why do you open the file using open? You don't seem to be using the file handle IN anywhere. But, when opening it, you correctly specify the path as "Output/$in". You should do the same when tying the file: `tie my @array, 'Tie::File', "Output/$in" or die ... # ~~~~~~~` [download] Otherwise, it just creates a new file in the current directory, populates its first line, and that's it. `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l] [select]
Re: Loop Through Files and Update Headers by kcott (Archbishop) on Mar 06, 2020 at 06:58 UTC
G'day jalopez453, As has already been mentioned, you've some problems in your code. Another, is "`untie @array`" inside the `for` loop: indenting your code probably would have made that more obvious. If you have a different number of new headers than what was there originally, consider using splice. Here's a quick example: `$ perl -E ' my @x = qw{H-old ...}; say for @x; splice @x, 0, 1, qw{H-new1 H-new2}; say for @x; ' H-old ... H-new1 H-new2 ...` [download] — Ken	[reply] [d/l] [select]
Re: Loop Through Files and Update Headers by choroba (Cardinal) on Mar 05, 2020 at 23:24 UTC
Crossposted to reddit. Next time, please, inform about crossposting to avoid unnecessary work of hackers not attending both the sites. `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l]
Re: Loop Through Files and Update Headers by Marshall (Canon) on Mar 07, 2020 at 03:32 UTC
I would not use Tie::File unless there is some user requirement of which I am not aware. I would read the input file into memory, save input file as a backup, modify input file as in memory, write modified contents to the output file. Untested, but hopefully gets you on the right track... use strict; use warnings; my $inDir ="."; my @inFiles = glob ("$inDir/*.txt"}; foreach my $infile (@inFiles) { # read infile into memory.. open IN, '<', "$inDir/$infile" or die "$!"; my @lines = <$infile>; close IN; # save the original infile rename ("$inDir/$infile", "$inDir/$infile-backup") or die "$!"; # modify the data that's in memory unshift @lines, "whatever_you_want\n"; #save the new data into the original file name open (OUT, '>', "$inDir/$infile") or die "$!"; print OUT @lines; close OUT; } [download] There are issues when "something goes wrong" and Tie::File. The above saves a "backup" in the case of problems.	[reply] [d/l]