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?1n"; ?

  
  

????????print?F51?"line?2n"; ?

  
  

????????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。