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Full Discussion: How to check if a unix text file is being accessed?
Top Forums UNIX for Dummies Questions & Answers How to check if a unix text file is being accessed? Post 26480 by oombera on Monday 19th of August 2002 02:42:40 PM
Old 08-19-2002
flock command in perl
I'm not sure if you use an error subroutine in case the file cannot be opened, closed, etc, but here's one possible way to code this:
Code:
open (file_label, "file_path") || Error('open', 'file');
flock (file_label, 1) || Error('lock', 'file');
my @array_name = <file_label>;
close (file_label) || Error ('close', 'file');

sub Error {
 print "Content-type: text/html\n\n";
 print "The server can't $_[0] the $_[1] : $! \n";
 exit;
}

This will request shared access to a file in order to read from it and then will store the whole file in an array.

Replace the '1' in the flock() command with a '2' if you want to request exclusive access to a file, in order to write to it.

added code tags for readability
Last edited by oombera; 02-19-2004 at 02:44 PM..
 

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LEARN ABOUT OSX

shasum5.12

SHASUM(1)						 Perl Programmers Reference Guide						 SHASUM(1)

NAME

       shasum - Print or Check SHA Checksums

SYNOPSIS

	Usage: shasum [OPTION] [FILE]...
	   or: shasum [OPTION] --check [FILE]
	Print or check SHA checksums.
	With no FILE, or when FILE is -, read standard input.

	 -a, --algorithm    1 (default), 224, 256, 384, 512
	 -b, --binary	    read files in binary mode (default on DOS/Windows)
	 -c, --check	    check SHA sums against given list
	 -p, --portable     read files in portable mode
				produces same digest on Windows/Unix/Mac
	 -t, --text	    read files in text mode (default)

	The following two options are useful only when verifying checksums:

	 -s, --status	    don't output anything, status code shows success
	 -w, --warn	    warn about improperly formatted SHA checksum lines

	 -h, --help	    display this help and exit
	 -v, --version	    output version information and exit

	The sums are computed as described in FIPS PUB 180-2.  When checking,
	the input should be a former output of this program.  The default mode
	is to print a line with checksum, a character indicating type (`*'
	for binary, `?' for portable, ` ' for text), and name for each FILE.

DESCRIPTION

       The shasum script provides the easiest and most convenient way to compute SHA message digests.  Rather than writing a program, the user
       simply feeds data to the script via the command line, and waits for the results to be printed on standard output.  Data can be fed to
       shasum through files, standard input, or both.

       The following command shows how easy it is to compute digests for typical inputs such as the NIST test vector "abc":

	       perl -e "print qw(abc)" | shasum

       Or, if you want to use SHA-256 instead of the default SHA-1, simply say:

	       perl -e "print qw(abc)" | shasum -a 256

       Since shasum uses the same interface employed by the familiar sha1sum program (and its somewhat outmoded anscestor md5sum), you can install
       this script as a convenient drop-in replacement.

AUTHOR

       Copyright (c) 2003-2008 Mark Shelor <mshelor@cpan.org>.

SEE ALSO

       shasum is implemented using the Perl module Digest::SHA or Digest::SHA::PurePerl.

perl v5.12.5							    2013-08-25								 SHASUM(1)
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