Want to protect your cyber security and still get fast solutions? Ask a secure question today.Go Premium

x
?
Solved

file counter?

Posted on 2000-04-03
6
Medium Priority
?
209 Views
Last Modified: 2013-12-25
how to make a file (exclusive)file counter?
0
Comment
Question by:syu1
  • 3
  • 2
6 Comments
 
LVL 16

Accepted Solution

by:
maneshr earned 80 total points
ID: 2681557
Here's how you increment a number in a file, using flock:

use Fcntl qw(:DEFAULT :flock);

sysopen(FH, "numfile", O_RDWR|O_CREAT)                                    or die "can't open numfile: $!";
flock(FH, LOCK_EX) or die "can't write-lock numfile: $!";

# Now we have acquired the lock, it's safe for I/O
$num = <FH> || 0;                   # DO NOT USE "or" THERE!!
seek(FH, 0, 0)                      or die "can't rewind numfile : $!";
truncate(FH, 0)                     or die "can't truncate numfile: $!";
print FH $num+1, "\n"               or die "can't write numfile: $!";
close(FH)                           or die "can't close numfile: $!";

Closing the filehandle flushes the buffers and unlocks the file.
===========================================
NOTE: truncate EXPR, LENGTH

This function truncates the file opened on FILEHANDLE, or named by EXPR, to the specified length.
0
 

Author Comment

by:syu1
ID: 2691940
thanks!

your answer is really work, but what is
 
truncate(FH, 0)                     or die "can't truncate numfile: $!";


really work?
0
 
LVL 85

Expert Comment

by:ozo
ID: 2692004
perldoc -f truncate
=item truncate FILEHANDLE,LENGTH

=item truncate EXPR,LENGTH

Truncates the file opened on FILEHANDLE, or named by EXPR, to the
specified length.  Produces a fatal error if truncate isn't implemented
on your system.  Returns TRUE if successful, the undefined value
otherwise.
0
Upgrade your Question Security!

Your question, your audience. Choose who sees your identity—and your question—with question security.

 
LVL 16

Expert Comment

by:maneshr
ID: 2693572
Syu1,
glad to know that the solution worked for you.


Also here is a brief note about truncate

truncate FILEHANDLE, LENGTH
truncate EXPR, LENGTH

This function truncates the file opened on FILEHANDLE, or named by EXPR, to the specified length. The function produces a fatal error if truncate(2) or an equivalent isn't implemented on your system. (You can always truncate a file by copying the front of it, if you have the disk space.)


truncate(FH, 0)                     or die "can't truncate numfile: $!";

what the above means is if truncate fails then show the Error message "can't truncate numfile: <actual error message" and exit the Perl program with a nonzero exit status.

Hope that helps
0
 

Author Comment

by:syu1
ID: 2697067
thanks lot! maneshr, I really appreciate it!
0
 
LVL 16

Expert Comment

by:maneshr
ID: 2698620
youre welcome :-)
0

Featured Post

[Webinar On Demand] Database Backup and Recovery

Does your company store data on premises, off site, in the cloud, or a combination of these? If you answered “yes”, you need a data backup recovery plan that fits each and every platform. Watch now as as Percona teaches us how to build agile data backup recovery plan.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

It is becoming increasingly popular to have a front-page slider on a web site. Nearly every TV website,  magazine or online news has one on their site, and even some e-commerce sites have one. Today you can use sliders with Joomla, WordPress or …
The Windows functions GetTickCount and timeGetTime retrieve the number of milliseconds since the system was started. However, the value is stored in a DWORD, which means that it wraps around to zero every 49.7 days. This article shows how to solve t…
In this seventh video of the Xpdf series, we discuss and demonstrate the PDFfonts utility, which lists all the fonts used in a PDF file. It does this via a command line interface, making it suitable for use in programs, scripts, batch files — any pl…
In a recent question (https://www.experts-exchange.com/questions/29004105/Run-AutoHotkey-script-directly-from-Notepad.html) here at Experts Exchange, a member asked how to run an AutoHotkey script (.AHK) directly from Notepad++ (aka NPP). This video…
Suggested Courses

581 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question