Perl: file operations, my, time conversion, log monitoring

① File Operations

To read a string from a file using Perl, you can use either of the following methods:
1. Read all the content in the file into an array at a time (this method is suitable for small files ):

  Open  (File  ,  "  Filename  "  )  |  Die  "  Can not open the file: $! "  ;
  @ Filelist  = <  File  >  ;

  Foreach     $ Eachline  (  @ Filelist  ){
  Chomp     $ Eachline  ;
}
 Close  File;
 

When the file is large, the "out of memory" error may occur. You can use the following method to read a row at a time.

2. Read and process one row from a file and one row at a time (it is more convenient to read large files ):

  Open  (File  ,  "  Filename  "  )  |  Die "  Can not open the file: $!  "  ;

  While  (  Defined  (  $ Eachline     = <  File  >  )){
  Chomp    $ Eachline  ;
  #  Do what u want here!  
  }
  Close  File; 

② Differences between our, my, and local

Http://www.cppblog.com/converse/archive/2008/07/31/57636.html

Http://topic.csdn.net/t/20000223/18/2737.html

Our: global variable definition. If the global variable has been defined in the function, it is equivalent to referencing the global variable. (All Access: upper-level, current, lower-level)

Local: localized the global variable (equivalent to a local global variable). After localization, all modifications to this variable derived from this local variable only affect this local variable. (Access: Current, lower-level)

My: a real local variable. This variable is valid only in this local environment and is invalid in subprocesses. (Access: current)

 

③ Time conversion (conversion between the date and time string formats used in daily use and epoch seconds)

Epoch to daily: $ common = localtime (time); # Second, minute, hour, day, month, year, day of the week, day of the year, and hour

Daily to epoch: $ epoch_seconds = timelocal ($ S, $ M, $ H, $ mday, $ Mon, $ year );

Http://muent.com/a/develop/AllDL/201004303575.html

 

④ Log monitoring

Simulate log writing:

 Use  Io  ::  Handle;
  Open  (FD  ,     "  > Test. Log "  ) Or  Die  $  !  ;
FD  ->  Autoflush (  1  );
  While  (  1  ){
  My     $ Now    =     Time  ;
  Print  FD  $ Now  ,     "  \ N  "  ;
  Sleep     1 ;
}
  Close  FD; 

Simulate monitoring log:

 Open  (FD  ,     "  <Test. Log  "  ) Or  Die  $  !  ;
  While (  1  ){
  My     $ In     =     <  FD  >  ;
  Print     $ In  ;
}
  Close FD; 

TIPS: You can enter <tail-F test. log | "during read"

 

⑤ Sub-process

Http://blog.csdn.net/aldenphy/archive/2009/11/03/4761585.aspx