使用Perl从文件读取

Question

I am learning Perl and have looked up this question but haven't been able to get it to work for me although it terminates without error.

I enter a file that it should want ( name-0-0-0 ) but it just skips the while loop altogether.

open FILE, '+>>userinfo.txt';
print("What is your name?");
$name = <>;
chomp $name;

while (<FILE>) {

chomp;
($nameRead,$wins, $losses, $cats) = split("-");

if ($nameRead eq $name){
    print("Oh hello $name, your current record is $wins wins - $losses losses - $cats ties");
    print("Would you like to play again? type y for yes or n for no\n");
    $bool = <>;
    if ($bool == "y"){
        print("Okay let's play!");
        play();
        exit();
    }
    else {
        printf("well fine goodbye!");
        exit();
    }

} 

}

Well it seems my problem was indeed related to the +>>. I am trying to add on to the file, but I wanted to be able to write, not just append. I changed it to +< and everything worked great. Thanks guys I really appreciate it!

Answer 1

I appears like you're using the wrong syntax to open the file for reading. Try

use autodie qw(:all);
open my $FILE, '<', '/path/to/file';

The syntax you're using opens a file for appending.

Answer 2

Your primary problem is that you have chosen an arcane open mode for userinfo.txt , which will allow you to open an existing file for both read and write but create a new file if it doesn't exist.

You must always check whether a file open has succeeded, and it looks like all you want to do is read from this file, so you want

open FILE, '<', 'userinfo.txt' or die $!;

You must also always add

use strict;
use warnings;

to the top of your program, and declare all variables with my at their first point of use.

Once you have made these changes you will most likely understand yourself what is going wrong, but if you have further problems please post your modified code.

Answer 3

The following says while you're reading the file and it hasn't reached the end of file:

while (<FILE>) {
   ...
}

You might want to remove the while loop entirely and just do everything inside it.

---

Edit/Alternative Solution:

The real reason nothing was happening is because when you use +>> , it opens the file up for read/append as you'd expect, but it immediately sets the cursor at the end of the file. So that when you encounter the while (<FILE>) { ... } there's nothing to read.

One solution would be to reset the file cursor position:

open FILE, '+>>userinfo.txt';
seek(FILE,0,0);                 # set the file cursor at the top

Answer 4

Why are you opening the file in +>> mode? That mode opens your file for input and output, but sets the filehandle cursor to the end of the file. Even experienced Perl programmers rarely have a need to do that.

Since the filehandle is positioned at the end of the file when you open it, you won't get anything when you attempt to read from it.

Is there a reason you aren't just saying open FILE, '<', 'userinfo.txt' ?