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Full Discussion: Removing older version files
Top Forums Shell Programming and Scripting Removing older version files Post 302766767 by alister on Tuesday 5th of February 2013 10:57:32 AM
Old 02-05-2013
Quote:
Originally Posted by balajesuri
Code:
#! /bin/bash

n=$1
x=`ls -l | wc -l`
for y in $(ls -1t | tail -$(( $x - $n ))); do rm -rf $y; done

Since ls is run twice, there's a race condition. If a directory is deleted in the meantime, a directory that should have been kept will be nuked. Similarly, if a directory is added in the meantime, a directory that should have been removed will persist.

There is no need to run ls twice. You can just use tail's ability to index releative to the beginning of the data, tail -n +10 versus tail -n 10. However, this approach still requires some arithmetic, since skipping the first x lines requires an option argument of x+1.

I wouldn't bother with tail. In my opinion, the simplest solution is to use sed:
Code:
ls -t | sed 1,10d | xargs rm -rf

Note that xargs does not play well with filenames containing whitespace or quotes. If such filenames occur, instead of xargs, a less efficient while-read loop would be necessary.
Code:
ls -t | sed 1,10d | while IFS= read -r dirname; do rm -fr "$dirname"; done

Regards,
Alister

Or, eve
 

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TAIL(1) 								FSF								   TAIL(1)

NAME
tail - output the last part of files SYNOPSIS
tail [OPTION]... [FILE]... DESCRIPTION
Print the last 10 lines of each FILE to standard output. With more than one FILE, precede each with a header giving the file name. With no FILE, or when FILE is -, read standard input. Mandatory arguments to long options are mandatory for short options too. --retry keep trying to open a file even if it is inaccessible when tail starts or if it becomes inaccessible later -- useful only with -f -c, --bytes=N output the last N bytes -f, --follow[={name|descriptor}] output appended data as the file grows; -f, --follow, and --follow=descriptor are equivalent -F same as --follow=name --retry -n, --lines=N output the last N lines, instead of the last 10 --max-unchanged-stats=N with --follow=name, reopen a FILE which has not changed size after N (default 5) iterations to see if it has been unlinked or renamed (this is the usual case of rotated log files) --pid=PID with -f, terminate after process ID, PID dies -q, --quiet, --silent never output headers giving file names -s, --sleep-interval=S with -f, sleep for approximately S seconds (default 1.0) between iterations. -v, --verbose always output headers giving file names --help display this help and exit --version output version information and exit If the first character of N (the number of bytes or lines) is a `+', print beginning with the Nth item from the start of each file, other- wise, print the last N items in the file. N may have a multiplier suffix: b for 512, k for 1024, m for 1048576 (1 Meg). With --follow (-f), tail defaults to following the file descriptor, which means that even if a tail'ed file is renamed, tail will continue to track its end. This default behavior is not desirable when you really want to track the actual name of the file, not the file descrip- tor (e.g., log rotation). Use --follow=name in that case. That causes tail to track the named file by reopening it periodically to see if it has been removed and recreated by some other program. AUTHOR
Written by Paul Rubin, David MacKenzie, Ian Lance Taylor, and Jim Meyering. 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 tail is maintained as a Texinfo manual. If the info and tail programs are properly installed at your site, the command info tail should give you access to the complete manual. tail (coreutils) 4.5.3 February 2003 TAIL(1)
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