#Open the 'txt' file for reading
open FH, '<', "$file_name.txt" or die "Error:$!\n";
#Open the 'txt' file for writing. Creates the #file_name if it doesn't already exist #and will delete/overwrite a pre-existing file of the same name
open FH, '>', "$file_name.txt" or die "Error:$!\n";
#Open the 'txt' file for appending. Creates the #file_name if it doesn't already exist
open FH, '>>', "$file_name.txt" or die "Error:$!\n";
#Open the 'txt' file for a 'read/write'. #Will not create the file if it doesn't #already exist and will not delete/overwrite #a pre-existing file of the same name
open FH, '+<', "$file_name.txt" or die "Error:$!\n";
#Open the 'txt' file for a 'read/write'. Will create #the file if it doesn't already exist and will #delete/overwrite a pre-existing file #of the same name
open FH, '+>', "$file_name.txt" or die "Error:$!\n";
#Open the 'txt' file for a 'read/append'. Will create #the file if it doesn't already exist and will #not delete/overwrite a pre-existing file #of the same name
open FH, '+>>', "$file_name.txt" or die "Error:$!\n";

#!/usr/bin/perl
use strict ;
use warnings ;
sub test{
    open FILE, '<', "d:/code/test.txt" or die $! ;
    my $olds = $/ ;
    $/ = undef ;
    my $slurp = <FILE> ;
    print $slurp, "\n" ;
    $/ = $olds ;
    close FILE;
}
&test() ;

#!/usr/bin/perl
use strict ;
use warnings ;
sub test{
    local $/ ; #??? local $/ = undef ;
    open FILE, '<', "d:/code/zdd.txt" or die $! ;
    my $slurp = <FILE> ;
    print $slurp, "\n" ;
}
&test() ;
1;

open FILE "<$file" or die $! ; #這樣可以。
open FILE '<$file' or die $! ; #這樣就不可以,因?yàn)?file不會(huì)被解釋成變量?jī)?nèi)插。同樣<也不會(huì)被解釋成輸入符號(hào)。

sub main {
    open FILE, '+<', 'test.data' or die $!;
    &test(*FILE);
    close FILE;
}

sub main {
    open my $FILE, '+<', 'test.data' or die $!;
    &test($FILE);
    close $FILE;
}