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Full Discussion: overwriting on a file
Special Forums UNIX Desktop Questions & Answers overwriting on a file Post 302700067 by Don Cragun on Thursday 13th of September 2012 01:13:55 AM
Old 09-13-2012
Any time you have a pipeline that reads from a file that is overwritten by a redirection at the end of the pipeline, you will lose data. The shell's will wipe out the current data in the file specified by the redirection before any command in the pipeline has a chance to read from it.

However, you could add:
Code:
        mv F2/$name /F1

after the pipeline starting with sort in your for loop as long as:
  1. There are no spaces, tabs, newlines, or other special characters in any of your filenames,
  2. there are no hard links to any of the file in directory F1, and
  3. you have sufficient space available on the file system.
If 1 or 3 above is not true, your script already has problems. If there are hard links to files in F1 that you need to preserve, your could replace the command added above with:
Code:
        cp F2/$name F1/$name && rm F2/$name

to preserve the links.

You could also simplify the and speed up your script if you replace:
Code:
sort  $X | uniq  | awk '{ $1=""}1' | awk '{ $NF=""}1'  > F2/${name}

in your loop with:
Code:
sort -u $X | awk '{ $NF="";$1=""}1' > F2/${name}

This User Gave Thanks to Don Cragun For This Post:
A-V
 

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LEARN ABOUT FREEBSD

dh_fixperms

DH_FIXPERMS(1)							     Debhelper							    DH_FIXPERMS(1)

NAME

       dh_fixperms - fix permissions of files in package build directories

SYNOPSIS

       dh_fixperms [debhelperoptions] [-Xitem]

DESCRIPTION

       dh_fixperms is a debhelper program that is responsible for setting the permissions of files and directories in package build directories to
       a sane state -- a state that complies with Debian policy.

       dh_fixperms makes all files in usr/share/doc in the package build directory (excluding files in the examples/ directory) be mode 644. It
       also changes the permissions of all man pages to mode 644. It removes group and other write permission from all files. It removes execute
       permissions from any libraries, headers, Perl modules, or desktop files that have it set. It makes all files in the standard bin and sbin
       directories, usr/games/ and etc/init.d executable (since v4). Finally, it removes the setuid and setgid bits from all files in the package.

       When the Rules-Requires-Root field has the (effective) value of binary-targets, dh_fixperms will also reset the ownership of all paths to
       "root:root".

OPTIONS

       -Xitem, --exclude item
	   Exclude files that contain item anywhere in their filename from having their permissions changed. You may use this option multiple
	   times to build up a list of things to exclude.

SEE ALSO

       debhelper(7)

       This program is a part of debhelper.

AUTHOR

       Joey Hess <joeyh@debian.org>

11.1.6ubuntu2							    2018-05-10							    DH_FIXPERMS(1)
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