Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
check_database
# Do the actual work.
echo
# You may wish to redirect the stdout of this script to a file,
#+ especially if the directory checked has many files in it.
# For a much more thorough file integrity check,
#+ consider the "Tripwire" package,
#+ http://sourceforge.net/projects/tripwire/.
exit 0
shred
See also Example A−20 for a creative use of the md5sum command.
Securely erase a file by overwriting it multiple times with random bit patterns before deleting it. This
command has the same effect as Example 12−42, but does it in a more thorough and elegant manner.
This is one of the GNU fileutils.
Advanced forensic technology may still be able to recover the contents of a file, even
after application of shred.
Encoding and Encryption
uuencode
This utility encodes binary files into ASCII characters, making them suitable for transmission in the
body of an e−mail message or in a newsgroup posting.
uudecode
This reverses the encoding, decoding uuencoded files back into the original binaries.
Example 12−30. uudecoding encoded files
#!/bin/bash
lines=35
# Allow 35 lines for the header (very generous).
for File in * # Test all the files in the current working directory...
do
search1=`head −$lines $File | grep begin | wc −w`
search2=`tail −$lines $File | grep end | wc −w`
# Uuencoded files have a "begin" near the beginning,
#+ and an "end" near the end.
if [ "$search1" −gt 0 ]
then
if [ "$search2" −gt 0 ]
then
echo "uudecoding − $File −"
uudecode $File
fi
fi
done
# Note that running this script upon itself fools it
#+ into thinking it is a uuencoded file,
Chapter 12. External Filters, Programs and Commands 189