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Full Discussion: Incredibly inefficient cat | grep script
Top Forums Shell Programming and Scripting Incredibly inefficient cat | grep script Post 302913044 by achenle on Wednesday 13th of August 2014 01:01:35 PM
Old 08-13-2014
What's the exact contents of each file?

Right now, you're literally running millions of greps, comparing each ID to every other ID. That's a huge waste of time, obviously. You only really need to compare each ID to itself.

Because it seems to me that you're just looking for IDs that are in both files. If each ID only occurs once in each file, pull the IDs out of each file, combine them into one file, sort them, and only count IDs that are duplicated in the combined file.

Or you can figure out how to use the "join" utility, though that may not be any faster than what you're already doing, although it does have the huge advantage of not having to fork() and exec() a new process millions of times.
 

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LEARN ABOUT MOJAVE

newgrp

NEWGRP(1)						    BSD General Commands Manual 						 NEWGRP(1)

NAME

     newgrp -- change to a new group

SYNOPSIS

     newgrp [-l] [group]

DESCRIPTION

     The newgrp utility creates a new shell execution environment with modified real and effective group IDs.

     The options are as follows:

     -l      Simulate a full login.  The environment and umask are set to what would be expected if the user actually logged in again.

     If the group operand is present, a new shell is started with the specified effective and real group IDs.  The user will be prompted for a
     password if they are not a member of the specified group.

     Otherwise, the real, effective and supplementary group IDs are restored to those from the current user's password database entry.

EXIT STATUS

     The newgrp utility attempts to start the shell regardless of whether group IDs were successfully changed.

     If an error occurs and the shell cannot be started, newgrp exits >0.  Otherwise, the exit status of newgrp is the exit status of the shell.

SEE ALSO

     csh(1), groups(1), login(1), sh(1), su(1), umask(1), group(5), passwd(5), environ(7)

STANDARDS

     The newgrp utility conforms to IEEE Std 1003.1-2001 (``POSIX.1'').

HISTORY

     A newgrp utility appeared in Version 6 AT&T UNIX.

BUGS

     Group passwords are inherently insecure as there is no way to stop users obtaining the crypted passwords from the group database.	Their use
     is discouraged.

BSD
								   May 23, 2002 							       BSD
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