perl不能写入文件内容的奇怪问题

sx98083714

open(ML,"+< mail_list.txt");
while(<ML>){
        chomp($_);
        my($user,$id,$mail)=split("\t",$_);
        chomp($id);
        $saved_mail{$id}=$mail;
}
......
                        print  ML "$u\t$id\t$mail\n";

程序运行到最后这一句时，死活就没有写入，我就奇了怪了。不知道问题到底是出在哪？谁有过类似遭遇？

sx98083714

mail_list.txt
这个文件没有其他程序在访问的。

sx98083714

气死了。死活都想不明白。

sx98083714

达人们快现身呀。

toniz

Mixing Reads and Writes

       It is possible to specify both read and write access.  All you do is add a "+" symbol
       in front of the redirection.  But as in the shell, using a less-than on a file never
       creates a new file; it only opens an existing one.  On the other hand, using a greater-
       than always clobbers (truncates to zero length) an existing file, or creates a brand-
       new one if there isn't an old one.  Adding a "+" for read-write doesn't affect whether
       it only works on existing files or always clobbers existing ones.

           open(WTMP, "+< /usr/adm/wtmp")
               || die "can't open /usr/adm/wtmp: $!";

           open(SCREEN, "+> lkscreen")
               || die "can't open lkscreen: $!";

           open(LOGFILE, "+>> /var/log/applog"
               || die "can't open /var/log/applog: $!";

       The first one won't create a new file, and the second one will always clobber an old
       one.  The third one will create a new file if necessary and not clobber an old one, and
       it will allow you to read at any point in the file, but all writes will always go to
       the end.  In short, the first case is substantially more common than the second and
       third cases, which are almost always wrong.  (If you know C, the plus in Perl's "open"
       is historically derived from the one in C's fopen(3S), which it ultimately calls.)

       In fact, when it comes to updating a file, unless you're working on a binary file as in
       the WTMP case above, you probably don't want to use this approach for updating.
       Instead, Perl's -i flag comes to the rescue.  The following command takes all the C,
       C++, or yacc source or header files and changes all their foo's to bar's, leaving the
       old version in the original filename with a ".orig" tacked on the end:

           $ perl -i.orig -pe 's/\bfoo\b/bar/g' *.[Cchy]

       This is a short cut for some renaming games that are really the best way to update
       textfiles.  See the second question in perlfaq5 for more details.

sx98083714

我分开写也不行呀
open(FH1,"xxx.txt")用来读取数据
open(FH2,">>xxx.txt")用来与入数据

这样也不行，又是为什么？

toniz

不读  直接写是否可以成功呢？

sx98083714

直接写应该没问题吧。我测试一下。

sx98083714

不读直接写没问题。

toniz

1. open(FH1,"t.t");
   
2. while(<FH1>){
   
3. print $_;
   
4. }
   
5. open(FH2,">>t.t");
   
6. 
   
7. print FH2 "kkkk\n";

复制代码

用这段测测有没问题