Solved

file counter?

Posted on 2000-04-03
6
199 Views
Last Modified: 2013-12-25
how to make a file (exclusive)file counter?
0
Comment
Question by:syu1
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 3
  • 2
6 Comments
 
LVL 16

Accepted Solution

by:
maneshr earned 20 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 84

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
DevOps Toolchain Recommendations

Read this Gartner Research Note and discover how your IT organization can automate and optimize DevOps processes using a toolchain architecture.

 
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

Free Tool: ZipGrep

ZipGrep is a utility that can list and search zip (.war, .ear, .jar, etc) archives for text patterns, without the need to extract the archive's contents.

One of a set of tools we're offering as a way to say thank you for being a part of the community.

Question has a verified solution.

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

Suggested Solutions

Title # Comments Views Activity
Support for Notepad++ (including downloading & installing a plugin) 5 246
Powershell File Sort 8 51
remove computer from using logon script 17 55
Powershell Split 18 43
Making a simple AJAX shopping cart Couple years ago I made my first shopping cart, I used iframe and JavaScript, it was very good at that time, there were no sessions or AJAX, I used cookies on clients machine. Today we have more advanced techno…
Recently I have been answering a lot of questions like this in IT forums that I frequent. The question posed is usually something along the lines of "We have software X installed and need to uninstall it for reason Y" or some other variant of the sa…
Learn how to match and substitute tagged data using PHP regular expressions. Demonstrated on Windows 7, but also applies to other operating systems. Demonstrated technique applies to PHP (all versions) and Firefox, but very similar techniques will w…
In this fifth video of the Xpdf series, we discuss and demonstrate the PDFdetach utility, which is able to list and, more importantly, extract attachments that are embedded in PDF files. It does this via a command line interface, making it suitable …

739 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