perl学习笔记(6)

学习文件操作。

句柄名字最好使用大写字母，这样就不会与保留字foreach,else,if等发生冲突。

如果文件句柄名字重复使用，即另一个文件用相同的文件句柄名字打开，那么原始文件句柄将先被关闭，然后重新打开。

打开文件时的异常处理：

$!在数字上下文中返回错误号，在字符串上下文中返回错误信息。

抛出异常信息时，die中断程序，warn不中断程序。

抛出异常信息时，带\n则不输出更多信息，否则要有at filename line XXX。

练习(f61.pl)：

$ cat f61.pl
#!/usr/bin/perl -w
open(F51,"XXXX.XX") or warn "Can not open file: $!";
open(F51,"XXXX,XX") or warn "Can not open file: $!\n";
open(F51,"abc.txt") or die "Can not open file: $!";
$contents = <F51>;
#chomp $contents;
print qq(\n\$contents=$contents);
@contents = <F51>;
#chomp @contents;
print qq(\n\@contents=@contents);
close(F51);
open(F51,"abc.txt") or die "Can not open file: $!";
print("\n use operator <> read lines: \n");
while(<F51>){
print(qq($_));
}
close(F51);

$ perl f61.pl

Can not open file: No such file or directory at f61.pl line 2.

Can not open file: No such file or directory

$contents=first line

@contents=second line

third line

use operator <> read lines:

first line

second line

third line

写文件和打开文件语法相似，不同的是路径前加>表示打开时先清空文件，>>表示从文件末尾添加。

练习(f62.pl):

#!/usr/bin/perl -w

open(F51,">efg.txt") or die $!;
print F51 "line 1\n";
print F51 "line 2\n";
print F51 "line 3";
close(F51);

print("\nshow file:\n");
system("cat efg.txt");

open(F51,">>efg.txt") or die $!;
print F51 "\nline 4";
close(F51);

print("\nshow file:\n");
system("cat efg.txt");

print("\n");

$ perl f62.pl

show file:

line 1

line 2

line 3

show file:

line 1

line 2

line 3

line 4

当你将数据写入一个文本文件时， P e r l将\ n字符序列转换成你的操作系统使用的记录分隔符。在U N I X中，\ n变成一个ASCII 10（L F）；在M a c i n t o s h上，\ n转换成ASCII 13（C R）；在D O S和Wi n d o w s系统上，它变成序列ASCII 13和ASCII 10（C R L F）。

每当你真的想要写入二进制数据并且不希望P e r l或操作系统对它进行转换时，你必须使用b i n m o d e函数，将文件句柄标记为二进制文件。应该在文件句柄打开之后和对它进行输入输出之前使用b i n m o d e。

open(F51,"abc.gif") or die "$!";

binmode(F51);

#...

print F51 "...";

#...

close(F51);

对文件进行检查：

-r File is readable by effective uid/gid.

-w File is writable by effective uid/gid.

-x File is executable by effective uid/gid.

-o File is owned by effective uid.

-R File is readable by real uid/gid.

-W File is writable by real uid/gid.

-X File is executable by real uid/gid.

-O File is owned by real uid.

-e File exists.

-z File has zero size (is empty).

-s File has nonzero size (returns size in bytes).

-f File is a plain file.

-d File is a directory.

-l File is a symbolic link.

-p File is a named pipe (FIFO), or Filehandle is a pipe.

-S File is a socket.

-b File is a block special file.

-c File is a character special file.

-t Filehandle is opened to a tty.

-u File has setuid bit set.

-g File has setgid bit set.

-T File is an ASCII text file (heuristic guess).

-B File is a "binary" file (opposite of -T).

-M Script start time minus file modification time, in days.

-A Same for access time.

-C Same for inode change time (Unix, may differ for other platforms)

Example:

while (<>) {

chomp;

next unless -f $_; # ignore specials

#...

}

看到一句话也许有用：getc能够从文件读取单字符输入。

继续学习：

不同的操作系统和不同的文件系统需要使用不同类型的锁定机制。

flock函数可以给UNIX和NT下的文件加锁。lock_SH共享锁，lock_EX专用锁。关闭文件自动释放锁，lock_UN释放锁很少需要这样做。

因为要先open后lock，这两个操作有空档，通过一个辅助文件可实现open前加锁。所有程序都先去锁信号文件，锁定信号文件成功后再open数据文件。

练习(f63.pl)：

#!/usr/bin/perl -w
use Fcntl qw(:flock);

my $lock_file1="/usr/tmp/lock1.lck";
sub get_lock1 {
open(LOCK1,">$lock_file1") or die $!;
flock(LOCK1,LOCK_EX) or die "Lock failed: $!";
}
sub release_lock1 {
close(LOCK1);
}
print "press any key to get lock1:";
$WAIT=<STDIN>;
get_lock1();
print("\nget lock1,input your text to file efg.txt: ");
open(F1,">efg.txt") or die $!;
$WAIT=<STDIN>;
print F1 $WAIT;
close(F1);
print("\npress any key to release lock1 and exit:");
$WAIT=<STDIN>;
release_lock1();
print qq(\n);

练习文件锁需要开两个窗口，下面是练习过程：









flock上锁不是操作系统级别的，只是程序之间的约定。例如：程序A用flock加锁，程序B不用flock仍然可以操作文件。flock用于A,B之间约定不要同时操作同一个文件。

这次就到这。

附件：http://down.51cto.com/data/2360042