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Top Forums UNIX for Dummies Questions & Answers Want to remove all lines but not latest 50 lines from a file Post 302868905 by drl on Tuesday 29th of October 2013 08:45:28 AM
Old 10-29-2013
Hi.

As alister said.

This behavior has been discussed in the forum, for example, I mentioned sponge / absorb for pipelines and re-writing-in-place in post #8 of https://www.unix.com/shell-programming-and-scripting/221749-run-command-without-over-writing.html -- that approach either keeps data in memory (say a perl array), or writes it to a scratch file first, both of which can preserve the inode if that is important. The sponge approach looks like the tee solution, but the internal logic differs by sponge collecting all the data until the end, then writing to the file argument, whereas tee streams the data to the file(s) as it comes in.

We cannot use the scratch file approach here because there is no additional disk space, so suggestions like the shell and dd above seemed appropriate. Both were validated on a file of 14M lines (~ 1 GB) with 50,000 lines being kept.

Best wishes ... cheers, drl

Last edited by drl; 10-30-2013 at 11:53 AM.. Reason: Minor typo.
 

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TEE(1)								   User Commands							    TEE(1)

NAME
tee - read from standard input and write to standard output and files SYNOPSIS
tee [OPTION]... [FILE]... DESCRIPTION
Copy standard input to each FILE, and also to standard output. -a, --append append to the given FILEs, do not overwrite -i, --ignore-interrupts ignore interrupt signals -p diagnose errors writing to non pipes --output-error[=MODE] set behavior on write error. See MODE below --help display this help and exit --version output version information and exit MODE determines behavior with write errors on the outputs: 'warn' diagnose errors writing to any output 'warn-nopipe' diagnose errors writing to any output not a pipe 'exit' exit on error writing to any output 'exit-nopipe' exit on error writing to any output not a pipe The default MODE for the -p option is 'warn-nopipe'. The default operation when --output-error is not specified, is to exit immediately on error writing to a pipe, and diagnose errors writing to non pipe outputs. AUTHOR
Written by Mike Parker, Richard M. Stallman, and David MacKenzie. REPORTING BUGS
GNU coreutils online help: <http://www.gnu.org/software/coreutils/> Report tee translation bugs to <http://translationproject.org/team/> COPYRIGHT
Copyright (C) 2017 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. SEE ALSO
Full documentation at: <http://www.gnu.org/software/coreutils/tee> or available locally via: info '(coreutils) tee invocation' GNU coreutils 8.28 January 2018 TEE(1)
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