Follow Techotopia on Twitter

On-line Guides
All Guides
eBook Store
iOS / Android
Linux for Beginners
Office Productivity
Linux Installation
Linux Security
Linux Utilities
Linux Virtualization
Linux Kernel
System/Network Admin
Scripting Languages
Development Tools
Web Development
GUI Toolkits/Desktop
Mail Systems
Eclipse Documentation

How To Guides
General System Admin
Linux Security
Linux Filesystems
Web Servers
Graphics & Desktop
PC Hardware
Problem Solutions
Privacy Policy




9.4. I/0 redirection and loops

9.4.1. Input redirection

Instead of controlling a loop by testing the result of a command or by user input, you can specify a file from which to read input that controls the loop. In such cases, read is often the controlling command. As long as input lines are fed into the loop, execution of the loop commands continues. As soon as all the input lines are read the loop exits.

Since the loop construct is considered to be one command structure (such as while TEST-COMMAND; do CONSEQUENT-COMMANDS; done), the redirection should occur after the done statement, so that it complies with the form

command < file

This kind of redirection also works with other kinds of loops.

9.4.2. Output redirection

In the example below, output of the find command is used as input for the read command controlling a while loop:

[carol@octarine ~/testdir] cat

# This script creates a subdirectory in the current directory, to which old
# files are moved.
# Might be something for cron (if slightly adapted) to execute weekly or 
# monthly.

ARCHIVENR=`date +%Y%m%d`

mkdir $DESTDIR

find $PWD -type f -a -mtime +5 | while read file
gzip "$file"; mv "$file".gz "$DESTDIR"
echo "$file archived"

Files are compressed before they are moved into the archive directory.

  Published under the terms of the GNU General Public License Design by Interspire