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

Hi Monks,

Title may be a bit misleading. I know how to read the last line of the file, but what I want to know is the best method to detect it. I have a simple text file with a bunch of e-mail addresses: 
blah@blah.com
blah@somedomain.com
blah@johndoe.com

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Now I want to read this file and print it out so I can copy and paste to my e-mail program (outlook) and send them a announement. So I want to print the content of this textfile into a textarea to copy and paste.

Heres my code that reads the file, and prints line by line into the textarea. 
    my $file = "emails.txt";
    open(FILE, $file) or die "cannot open $file : $!\n";
    @content = reverse (<FILE>);
    close FILE;

print "<textarea cols=\"75\" rows=\"22\">";
foreach $address (@content) {
chomp($address);
print "$address, ";
}
print "</textarea>";

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Now heres my problem, the above code prints this into the textarea: 
blah@johndoe, blah@somedomain.com, blah@blah.com,

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Notice the comma at end (blah@blah.com,), how can I detect the end of the line of this file so I can tell Perl not to print the last "," ? So basically I want the contents of textarea to look like thisblah@johndoe, blah@somedomain.com, blah@blah.com

I'm building this as a add-on to a newsletter script so my friend (whose not really good with computers) can goto this script and copy the e-mails from the textarea box and paste it directly into her Outlook address. I really would like to learn this and give her extra convenience by not having her delete the last trailing "," manually.

Thanks Monks

Replies are listed 'Best First'.
Re: Detecting Last line of a file
by gam3 (Curate) on Jun 18, 2005 at 11:19 UTC
    Use join: 
    ...
    chomp @content;
print join(', ', @content);

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    ...

    -- gam3
    A picture is worth a thousand words, but takes 200K.
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Re: Detecting Last line of a file
by davidrw (Prior) on Jun 18, 2005 at 13:26 UTC
    The join method is definitely the way to go in this case, but to answer more generally (there was a recent node about this: Don't print on the last loop , but i can't find it at the moment Update Thanks omega_monk!), if you just flip the thought process and prepend commas instead of append them, it becomes: 
    my $addrCt = 0;
foreach $address (@content) {
  print ", " if $addrCt++;  # won't be done the first time
  chomp($address);
  print $address;
}

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      I believe the node that you are referring to is 466164.
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      Rather than keeping an extra variable around just test $address:

      print ", " if $address; # won't be done the first time

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      Perl is Huffman encoded by design.
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        Why wouldn't it be done the first time? That doesn't work unless $content[0] is somehow false .. since we're looping through @content and they're presumably all non-false, then $address is always set. Best way to get rid of the temp var is to just use split, or dpending on context (i.e. if you're reading a file) you could do print "," if $. > 1;.
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Re: Detecting Last line of a file
by data64 (Chaplain) on Jun 18, 2005 at 14:46 UTC

    To detect last line of file, use the "eof" function. Check perlfunc for more informtion about eof

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      Yeah, this EOF seems like a good way to go. It's addressed in some, but not all (eg, not the activestate) perlfaq5:

      "How do I change one line in a file/delete a line in a file/insert a line in the middle of a file/append to the beginning of a file?

      .....

      The following code snippet deletes the last line of a file without making a copy or reading the whole file into memory: 

              open (FH, "+< $file");
        while ( <FH> ) { $addr = tell(FH) unless eof(FH) }
        truncate(FH, $addr);"

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      Presumably you can modify this to do things other than deleting. Hope this helps!

      Or, you could do like the most recent perlfaq5 suggests and use Tie::File:

      "How do I change one line in a file/delete a line in a file/insert a line in the middle of a file/append to the beginning of a file? Use the Tie::File module, which is included in the standard distribution since Perl 5.8.0."

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Re: Detecting Last line of a file
by chas (Priest) on Jun 18, 2005 at 12:21 UTC
    Or perhaps (after chomping if necessary) 
    print shift @content;
for(@content){print ", $_";}

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    chas
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Re: Detecting Last line of a file
by g0n (Priest) on Jun 18, 2005 at 10:49 UTC
    This might not be the best way, but it should work:

    Update: It isn't the best way, isn't even a good way. See later in the thread for better solutions. Doh!

        my $file = "emails.txt";
    open(FILE, $file) or die "cannot open $file : $!\n";
    @content = reverse (<FILE>);
    close FILE;

print "<textarea cols=\"75\" rows=\"22\">";
foreach $address (@content) {
chomp($address);
print $address;
if ($address ne $content[-1]){print ", "}
}
print "</textarea>";

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    (In other words, print the comma unless its the last line). That assumes that each element in @content is unique. Given that you are using them for a mailing list, that should be a valid assumption. If not: 

    ..
my $counter=0;
foreach $address (@content) {
chomp($address);
print $address;
$counter++;
if ($counter < @content){print ", "}
}
..

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    Set a counter and print the comma if the counter is smaller than the number of elements in the array.

    --------------------------------------------------------------

    g0n, backpropagated monk

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