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Top Forums UNIX for Dummies Questions & Answers File comparison of huge files Post 302588084 by Corona688 on Friday 6th of January 2012 04:15:32 PM
Old 01-06-2012
Quote:
Originally Posted by kaaliakahn
Thanks ctsgnb.


Could you please explain why do you need to sort?
It's the simplest and most reliable way to tell whether a line's a duplicate or not. sort is actually pretty sophisticated, capable of handling extremely huge files without bogging down. Once it's done so, any duplicate lines will show up all in a row, letting you use uniq to get rid of them.
Quote:
Thirdly please explain why use mknod?
He's actually making a named pipe. On many systems you can just use mkfifo for that.

A named pipe lets you do this:

Code:
mkfifo fifo
cat file > fifo &
cat fifo # the first cat writes to the fifo, the second cat reads from it.
# This is effectively cat file | cat.
# Named pipes can be a handy way to join together programs which
# read from filenames and can't easily handle stdin/stdout communication.

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MKFIFO(2)						      BSD System Calls Manual							 MKFIFO(2)

NAME
mkfifo -- make a fifo file LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <sys/stat.h> int mkfifo(const char *path, mode_t mode); DESCRIPTION
mkfifo() creates a new fifo file with name path. The access permissions are specified by mode and restricted by the umask(2) of the calling process. The fifo's owner ID is set to the process's effective user ID. The fifo's group ID is set to that of the parent directory in which it is created. RETURN VALUES
A 0 return value indicates success. A -1 return value indicates an error, and an error code is stored in errno. ERRORS
mkfifo() will fail and no fifo will be created if: [EOPNOTSUPP] The kernel has not been configured to support fifo's. [ENOTDIR] A component of the path prefix is not a directory. [ENAMETOOLONG] A component of a pathname exceeded {NAME_MAX} characters, or an entire path name exceeded {PATH_MAX} characters. [ENOENT] A component of the path prefix does not exist. [EACCES] Search permission is denied for a component of the path prefix. [ELOOP] Too many symbolic links were encountered in translating the pathname. [EROFS] The named file resides on a read-only file system. [EEXIST] The named file exists. [ENOSPC] The directory in which the entry for the new fifo is being placed cannot be extended because there is no space left on the file system containing the directory. [ENOSPC] There are no free inodes on the file system on which the fifo is being created. [EDQUOT] The directory in which the entry for the new fifo is being placed cannot be extended because the user's quota of disk blocks on the file system containing the directory has been exhausted. [EDQUOT] The user's quota of inodes on the file system on which the fifo is being created has been exhausted. [EIO] An I/O error occurred while making the directory entry or allocating the inode. [EIO] An I/O error occurred while reading from or writing to the file system. [EFAULT] path points outside the process's allocated address space. SEE ALSO
chmod(2), stat(2), umask(2) STANDARDS
The mkfifo function call conforms to ISO/IEC 9945-1:1990 (``POSIX.1''). BSD
June 4, 1993 BSD
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