Replace multiple files in a directory using Perl

Question

Update: I modified my code but it still can't update all the files properly (no compilation issues and I can open/read all the files as well). Can someone please take a look what I am doing wrong. My updated code is below:

I have a follow-on question that I asked earlier. I have a directory named Perl which has three .txt files, namely fil1.txt, file2.txt and file 3.txt.

Content of file 1

line1
line2
TAG1 "some_name:tag1"
line4
TAG2 "some_name:tag2"
line5
TAG3 "some_name:tag3"

Content of file2.txt

line1
line2
TAG1 "some_name_file2:tag1"
line4
TAG2 "some_name_file2:tag2"
line5
TAG3 "some_name_file2:tag3"

Content of file3.txt

line1
line2
TAG1 "some_name_file3:tag1"
line4
TAG2 "some_name_file3:tag2"
line5
TAG3 "some_name_file3:tag3"

I want to replace all the lines that begin with the TAG with "hello_wolrd" such that the line should be something like this:

TAG1 "hello_world"
TAG2 "hello_world_2nd_time"
TAG3 "hello_world_3rd_time".

How do I achieve this? I get the error message that reads "Can't open the file" Here is my code:

  #! /usr/bin/perl

use strict;
use warnings;
use Data::Dumper;


my $dir = "path to my dir";
my @tmp = ();

opendir( my $DIR, "$dir") or die "Can't open directory, $!";
my @list = readdir($DIR);
my @list2 = sort grep(/^.*\.txt$/, @list);

foreach(@list2)
{
    push(@tmp, "$_\n");
}
closedir ($DIR);

print ("Tmp = @tmp\n");
foreach my $cur_file (<@tmp>) {

    my $fh;

    print "Current file = $cur_file\n";
    open($fh, '<', "$cur_file") or die "Can't open the file\n";
    while(<$fh>){
        chomp($_);
        my $line = $_;
        print "Current line is $line\n";
        if($line =~ /Tag1/)
        {
            $line =~s/\"\S+\"/"hello_world_1st_time"/g;
            push(@tmp, "$line\n");
        }
        elsif($line =~ /Tag2/)
        {
            $line =~s/\"\S+\"/"hello_world_2nd_time"/g;
            push(@tmp, "$line\n");
        }
        elsif($line =~ /Tag3/)
        {
            $line =~s/\"\S+\"/"hello_world_3rd_time"/g;
            push(@tmp, "$line\n");
        }
        else 
        {
            push(@tmp, "$line\n");
        }
    }       

    close($fh);

#   print Dumper @tmp;
    open ($fh, '>', "$cur_file") or die "Can't open file\n";
    print $fh @tmp;
    close($fh);
    undef @tmp;

}

You are doing yourself no favours by abstracting your example so far from your real code. What is Path to perl directory, for instance? It makes a big difference. — Borodin
– Borodin, Commented Apr 14, 2014 at 21:45
It seems to me that $cur_file will now contain a trailing newline. Try printing it as first thing in the for loop with some end-marks like this: print ">$cur_file<\n"; — szabgab
– szabgab, Commented Apr 16, 2014 at 4:41
Another thing, you'd be probably better off reading the lines into $line directly. while (my $line = <$fh>) — szabgab
– szabgab, Commented Apr 16, 2014 at 4:53

Miller · Accepted Answer · 2014-04-14 21:30:58Z

1

You're using single quotes around your filename:

open($fh, '<', '$cur_file') or die "Can't open the file\n";

To fix, just remove the single quotes:

open($fh, '<', $cur_file) or die "Can't open the file\n";

Additionally, you should get more helpful error messages by examining $!. If you had, you would've been told exactly why it couldn't open the file.

However, for an easier solution, just put use autodie; at the top of your script below your use strict; and use warnings; statements. If you had that, you would've gotten the following error message:

Can't open '$cur_file' for reading: 'No such file or directory'

answered Apr 14, 2014 at 21:30

Miller

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3 Comments

Birei Over a year ago

That is one of the errors, but there are some more. For example, the glob doesn't read contents from a directory. It should pass a basic regular expression or use readdir(). And it neither uses a regular expression comparison ignoring case, to say a few. Besides that, use an array hardcoding the text instead of replacing it, is very weird for me.

Borodin Over a year ago

@Birei: You should post your additional notes an an answer of your own

Miller Over a year ago

@Birei The fact that the OP reached the line to fail to open implies he has something in the glob that works. He also is printing out the contents of $cur_file before trying to open, so I think it's fair to assume he's already verified that works correctly.

Birei · Accepted Answer · 2014-04-14 21:58:21Z

I prefer to solve this kind of tasks using the -p (or -n) with -i switches. It creates a backup an iterates over all input files automatically. You save a lot of typing:

perl -i.bak -pe '
    BEGIN { %pos = qw{1 1st 2 2nd 3 3rd} } 
    s/^(TAG)(\d+)(\s+)(.*)$/$1 . $2 . $3 . "hello_world_" . $pos{$2} . "_time"/e
' ./your/dir/*.txt

The BEGIN block only is executed once and I create a hash to replace each number with its position, and the substitution instruction runs for each line of all input files, and when it finds a line that begins with TAG followed by a number, it checks the hash and replaces the whole line. In my testt it yields:

==> your/dir/file1.txt <==
line1
line2
TAG1 hello_world_1st_time
line4
TAG2 hello_world_2nd_time
line5
TAG3 hello_world_3rd_time

==> your/dir/file2.txt <==
line1
line2
TAG1 hello_world_1st_time
line4
TAG2 hello_world_2nd_time
line5
TAG3 hello_world_3rd_time

==> your/dir/file3.txt <==
line1
line2
TAG1 hello_world_1st_time
line4
TAG2 hello_world_2nd_time
line5
TAG3 hello_world_3rd_time

szabgab · Accepted Answer · 2014-04-16 05:10:30Z

#! /usr/bin/perl

use strict;
use warnings;


my $dir = "path to my dir";

opendir( my $DIR, "$dir") or die "Can't open directory, $!";
while (my $file = readdir $DIR) {
    next if $file !~ /\.txt$/;
    say $file;
    open($in, '<', $cur_file) or die "Can't open the file '$cur_file'\n";
    my @lines = <$in>;
    close $in;
    foreach my $line (@lines) {
        if($line =~ /Tag1/)
        {
            $line =~ s/"\S+"/"hello_world_1st_time"/g;
        }
        elsif($line =~ /Tag2/)
        {
            $line =~ s/"\S+"/"hello_world_2nd_time"/g;
        }
        elsif($line =~ /Tag3/)
        {
            $line =~ s/"\S+"/"hello_world_3rd_time"/g;
        }
    }       

    open ($out, '>', $cur_file) or die "Can't open file '$cur_file'\n";
    print $out @lines;
    close($out);
}


closedir $DIR;

Alternatively, use Path::Tiny as you can see in this article: http://perlmaven.com/how-to-replace-a-string-in-a-file-with-perl and if you need to do this in a whole directory tree, this article might help: http://perlmaven.com/finding-files-in-a-directory-using-perl

(disclaimer: I run the Perl Maven site)

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