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Full Discussion: Unix shell scripting
Top Forums Shell Programming and Scripting Unix shell scripting Post 302074366 by azrealhk on Tuesday 23rd of May 2006 12:19:16 AM
Old 05-23-2006
I have seen ls, wc etc give false readings if the file is opened by another program which is writing to it.

if the output is not flushed then file size etc remains the same.
try....

# cat flush.pl
#!/usr/local/bin/perl
open FH, ">flush.txt";
for (1..410) {
print FH "abcdefg89\n";
}
sleep 360;
close FH;

NOTE: The string is 10 chars (including \n), 410 lines written before sleep. therefore size should be 4100 bytes. The file is already open and not close yet on the sleep.

# tail flush.txt
abcdefg89
abcdefg89
abcdefg89
abcdefg89
abcdefg89
abcdefg89
abcdefg89
abcdefg89
abcdefg89
abcdefg89
abcdef

The block size of our system is 4096 so instead of 4100 bytes, 4096 is seen. The tail command will only show upto 4096 bytes.

# ls -l flush.txt
-rw-r--r-- 1 root system 4096 May 23 12:06 flush.txt

Ls confirms only 4096 bytes is seen

# wc -l flush.txt
409 flush.txt

wc -l shows only 409 and note 410.

The file will only show 4100 when you close the file.

# ls -l flush.txt
-rw-r--r-- 1 root system 4100 May 23 12:18 flush.txt
 

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FS_FLUSH(1)						       AFS Command Reference						       FS_FLUSH(1)

NAME
       fs_flush - Forces the Cache Manager to discard a cached file or directory

SYNOPSIS
       fs flush [-path <dir/file path>+] [-help]

       fs flush [-p <dir/file path>+] [-h]

DESCRIPTION
       The fs flush command removes from the cache all data and status information associated with each specified file or directory. The next time
       an application requests data from the flushed directory or file, the Cache Manager fetches the most current version from a File Server,
       along with a new callback (if necessary) and associated status information. This command has no effect on two types of data:

       o   Data in application program buffers.

       o   Data that has been changed locally and written to the cache but not yet written to the copy on the file server machine.

       To flush all data in the cache that was fetched from the same volume as a specified file or directory, use the fs flushvolume command.  To
       flush a corrupted mount point, use the fs flushmount command.

OPTIONS
       -path <dir/file path>+
	   Names each file or directory to flush from the cache. If it is a directory, only the directory element itself is flushed, not data
	   cached from files or subdirectories that reside in it. Partial pathnames are interpreted relative to the current working directory,
	   which is also the default value if this argument is omitted.

       -help
	   Prints the online help for this command. All other valid options are ignored.

EXAMPLES
       The following command flushes from the cache the file "projectnotes" in the current working directory and all data from the subdirectory
       "plans":

	  % fs flush -path projectnotes ./plans/*

PRIVILEGE REQUIRED
       The issuer must have the "l" (lookup) permission on the ACL of the root directory of the volume that houses the file or directory named by
       the -path argument, and on the ACL of each directory that precedes it in the pathname.

SEE ALSO
       fs_flushmount(1), fs_flushvolume(1)

COPYRIGHT
       IBM Corporation 2000. <http://www.ibm.com/> All Rights Reserved.

       This documentation is covered by the IBM Public License Version 1.0.  It was converted from HTML to POD by software written by Chas
       Williams and Russ Allbery, based on work by Alf Wachsmann and Elizabeth Cassell.

OpenAFS 							    2012-03-26							       FS_FLUSH(1)
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