Question

I’m trying to write a BASH script for patching my CentOS servers. My goal is that when I run the script, it outputs the package name, the currently installed version, and new package version. Something like this:

nspr.x86_64 / 4.8.8-3.el6 / 4.8.9-3.el6_2

This way, if I ever need to downgrade because a package broke something, I have a record of this.

The command yum check-update command gives me the 1st piece of information (the package name) and the 3rd piece of information (the new version) listed above, and I can use awk to separate the two. It’s easy after that; just run rpm -q {package} to get the 2nd piece of information, then concatenate them.

However, I’m running into trouble with the for loop in my code. I need to pass multiple arguments into the loop (the package name and newer version) so I can echo them later.

Here’s my code:

for package in `/usr/bin/yum --cacheonly --noplugins check-update | awk '{print $1, $2}'`;
do
    OLD_VER=`rpm -q ${package}` # ${package} should actually be $1 from the awk statement above

    NEW_VER=${2} # This is $2 from the awk statement above

    echo "${package} / ${OLD_VER} / ${NEW_VER}"
done

Pardon the obvious errors in the code; I’m new to BASH scripting. My confusion mostly stems from awk; I’m not very familiar with it, nor how it interacts with a BASH script. However, I think it’s clear what I’m trying to do. Does package get passed as an array? Is there a better way to do this?

Answer 1

you want to read the whole line:

 /usr/bin/yum --cacheonly --noplugins check-update |
 while read line; do
   set - $line;
   echo first: $1 second: $2
 done