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Full Discussion: edit sed command
Top Forums Shell Programming and Scripting edit sed command Post 302648197 by Corona688 on Tuesday 29th of May 2012 11:54:38 AM
Old 05-29-2012
Of course it "stalls", it has to read 9 whole gigs of data before it can do anything else and tries to keep the entire 500,000 lines of data in memory at once. Processing 9 gigs of data is going to take a while no matter how you cut it, and it won't find the data it wants until it's nearly done. To get the last 500,000 lines, it has to figure out where the end is, then back up from there...

Some implementations of 'tac' however, work by seeking, which would avoid having to read the first 99% of the file. It'd deliver them in reverse order so you could just head to get the number of lines you want, then reverse it again. I'm not sure Sun's does, but it's worth a shot:

Code:
tac filename | head -n 500000 > /tmp/$$
tac /tmp/$$ > /tmp/$$-forward
rm -f /tmp/$$

If Sun's tac doesn't do that, maybe you can install GNU tac.
Last edited by Corona688; 05-29-2012 at 01:00 PM..
 

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LEARN ABOUT OPENSOLARIS

tac

TAC(1)								   User Commands							    TAC(1)

NAME

       tac - concatenate and print files in reverse

SYNOPSIS

       tac [OPTION]... [FILE]...

DESCRIPTION

       Write each FILE to standard output, last line first.  With no FILE, or when FILE is -, read standard input.

       Mandatory arguments to long options are mandatory for short options too.

       -b, --before
	      attach the separator before instead of after

       -r, --regex
	      interpret the separator as a regular expression

       -s, --separator=STRING
	      use STRING as the separator instead of newline

       --help display this help and exit

       --version
	      output version information and exit

AUTHOR

       Written by Jay Lepreau and David MacKenzie.

REPORTING BUGS

       Report bugs to <bug-coreutils@gnu.org>.

COPYRIGHT

       Copyright (C) 2006 Free Software Foundation, Inc.
       This   is   free   software.    You   may   redistribute   copies   of	it   under   the   terms   of	the  GNU  General  Public  License
       <http://www.gnu.org/licenses/gpl.html>.	There is NO WARRANTY, to the extent permitted by law.

SEE ALSO

       The full documentation for tac is maintained as a Texinfo manual.  If the info and tac programs are properly installed at  your	site,  the
       command

	      info tac

       should give you access to the complete manual.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +--------------------+--------------------+
       |  ATTRIBUTE TYPE    |  ATTRIBUTE VALUE	 |
       +--------------------+--------------------+
       |Availability	    | SUNWgnu-coreutils  |
       +--------------------+--------------------+
       |Interface Stability | Uncommitted	 |
       +--------------------+--------------------+
NOTES

       Source for GNU coreutils is available on http://opensolaris.org.

tac 6.7 							   December 2006							    TAC(1)
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