perl leaving out the last value?

perllearner007 has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks, So I have two .txt files

File 1
Start    Stop   Name
234     388    abc
458     267    pqr
...
...
873     490    xyz
[download]

File 2

Name

abc
dfr
hyt
hig
wer
pqr
...
...
xyz
[download]

What I have done is read the file 2 names and if they occur in file 1 then get an output for those names with their respective start and stops. For eg: abc and pqr of file 2 occur in file 1 hence,

Output file
234     388    abc
458     267    pqr
[download]

What my problem is that the last entry which is 873 490 xyz should appear as the last entry in my output file but it isn't. I get all the others but the last entry isn't showing up on my output file. Any idea as to why this must be happening? Here is my code:

#!/usr/bin/perl


# Open  info file, and read in all the name start and stops
my $input_file = "/Users/myfolder/inputfile.txt";
die "Cannot open $input_file\n" unless (open(IN, $input_file));

my %name_and_Start_Stop;
while (chomp($line = <IN>))
{
    my (@columns) = split /\s+/, $line;
    my $name = $columns[3];
    my $Start = $columns[1];
    my $Stop = $columns[2];
        $name_and_Start{$name} = $Start;
        $name_and_Stop{$name} = $Stop;
}
close(IN);

# Open the input file, and read each name
die "name_list.txt" unless open(IN, "name_list.txt");

#Open output file and write the name start and stops
die "output.txt" unless(open(OUT,"> output.txt"));

while (chomp($symbol = <IN>))
{
    my $Start = $name_and_Start{$name};
    my $Stop = $name_and_Stop{$name};
        print OUT "$Start\ $Stop \ $name \n";
}
close(OUT);
close(IN);
[download]

Why isn't it outputting the last name xyz? Is it something in the split function?

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Re: perl leaving out the last value? by tobyink (Canon) on Apr 17, 2012 at 21:55 UTC
Here's your problem: `while (chomp($symbol = <IN>))` [download] The `chomp` function returns the number of characters chopped off the end of the line. `chomp` removes is a line break character. If you have no line break at the end of your text file, then chomp will not remove any characters, thus returns 0. So for the last line, you end up with: `while (0)` [download] So the block does not get executed. Try replacing constructions like this: `while (chomp($symbol = <IN>)) {` [download] with this instead: `while (defined($symbol = <IN>)) { chomp($symbol);` [download] `perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'`	[reply] [d/l] [select]
Re^2: perl leaving out the last value? by Eliya (Vicar) on Apr 17, 2012 at 22:14 UTC
`while (defined($symbol = <IN>))` With this particular construct, Perl automatically adds the `defined()`, so you can safely omit it if you prefer brevity. `$ perl -MO=Deparse -e'while ($symbol = <IN>) { chomp($symbol) }' while (defined($symbol = <IN>)) { chomp $symbol; } -e syntax OK` [download]	[reply] [d/l] [select]
Re: perl leaving out the last value? by davido (Cardinal) on Apr 17, 2012 at 21:59 UTC
This line (repeated twice with different identifiers): `while (chomp($symbol = <IN>))` [download] ... doesn't do what you want. chomp returns the total number of characters removed. Your last line has no line ending, so no characters are being removed. Since no characters are being removed, the return value of chomp, on the last iteration, is the moral equivelant of 'false'. Thus, the `while()` loop terminates without processing the last line. Move the chomp inside the loop. Additional reference on using the diamond operator: <>, truth and falsehood, and while loops. Also perfaq5. Three of those links provide examples of where to place the chomp. Update: The documentation for chomp may actually contribute to confusion, since it shows both the correct placement within a `while(){}` loop, and also an example of how to chomp a single file-read outside of the context of a loop, in a way that would be inappropriate in a `while` loop. Dave	[reply] [d/l] [select]
Re: perl leaving out the last value? by perllearner007 (Acolyte) on Apr 17, 2012 at 22:52 UTC
Thank you all for your replies! I am revising it..Will update if I still face any issues. Thanks again.	[reply]