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Full Discussion: Want to remove all lines but not latest 50 lines from a file
Top Forums UNIX for Dummies Questions & Answers Want to remove all lines but not latest 50 lines from a file Post 302868797 by drl on Monday 28th of October 2013 09:34:41 PM
Old 10-28-2013
Hi, RudiC.
Quote:
Originally Posted by RudiC
For discussion:
Code:
tac < file | head -5 | tac | tee file >/dev/null

...
Using the data and framework in the previous posts (14M lines, about 1 GB), I get:
Code:
tac: standard input: read error: Inappropriate ioctl for device
  30442 2334740 data1

not 50000 as desired.

The timing was:
Code:
real	0m35.072s
user	0m2.732s
sys	0m10.137s

The number of lines in the result varied, of 4 times, it did get 50000 once, the other 3 were 27K, 29K, and 30K, all of the latter with the ioctl message.

This is just for this 3GB workstation, a single datapoint.

Best wishes ... cheers, drl
Last edited by drl; 11-02-2013 at 02:27 PM.. Reason: Minor typo.
This User Gave Thanks to drl For This Post:
RudiC
 

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LEARN ABOUT REDHAT

tac

TAC(1)									FSF								    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) 2002 Free Software Foundation, Inc.
       This is free software; see the source for copying conditions.  There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICU-
       LAR PURPOSE.

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.

tac (coreutils) 4.5.3						   February 2003							    TAC(1)
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