Hacking_and_Penetration_Testing_with_Low_Power_Devices

68 CHAPTER 4 Filling the toolbox
download link (not a script) for my script to work properly. I have yet to find a case
where such a link wasn’t available.
The second new item in this script is the use of a regular expression in the sed substitution
on the line fname¼$(echo $fname j sed "s/\.${extension}$/\.deb/").
Recall that the most common use of sed is to replace one string with another.
So far, we search for an exact phrase. Sed expects a regular expression to be used
in searches. The period is a special character that matches any character in regular
expressions. We must escape it with a backslash (\) to tell sed that we really mean a
period. Our search string “\.${extension}$” matches a period, followed by the contents
of the extension variable if and only if it occurs at the end of the line thanks to
the trailing dollar sign. This period plus extension is replaced with “.deb”:
#!/bin/bash
# This script will iterate over the packages-to-download.txt
# file and ask the user to verify the correct command to download
# and then install the package.
#
# Originally created by Dr. Phil Polstra
# for the book
# Hacking and Penetration Testing With Low Power Devices
# we need wget
WGET¼'which wget'
#check for our file
[ -e packages-to-download.txt ] jj ( echo "packages-to-download.txt\
not found" && exit -1 )
# This function will verify URL and then download a pkg
dl_pkg () {
echo -n\
"Enter the correct URL to download $pkg or press Enter for $url> "
read resp
# if they didn't just press update the $url
if [ "$resp" !¼ "" ] ; then
$url ¼ $resp
fi
fname¼$(echo $url j tr "/" "\n" j tail -1)
# download using wget
if [ ! -e "/tmp/${fname}" ] ; then
‘$WGET ${url} -O /tmp/${fname}‘
fi
}
#install the package
install_pkg () {