Using a Script to Edit a conf File

Well, because I have been uber busy here at work, I haven't been able to write any blog posts. But, since I've been super productive at work, I get to write up a few posts about some more tools I've written to add to my arsenal. w00t!

So my latest task involved editing some of our web server's Apache confs. It consisted of adding a new alias so that we can call in some new app someone else wrote. Okay cool. Alias? Sure not a problem. Er...wait! The alias requires the site's directory name as part of the path! Oh no! That means I can't create one global alias!

Ah, see that's when I thought of writing this script that will look for a specific line in the vhost entries and will enter the new line after it. Pretty nifty eh? :)

So basically, what we have here is a list of all sites in a text file. Now we can use the site's directory name read in as a variable. It will then use awk to search for a specific line, and then print the new line you need right below it!

So if you take a look at the code, I want to add this line:
"Alias /newalias /mnt/www/$site" (where $site is the site directory name variable)
right after each line that fits the regex that searches for any line that has "Alias" and "reports" in one line followed by the site dir name at the end of the line. Obviously if you want to utilize this script you should edit the regex to your needs.

And that's it! Now think of all of the time saved rather than adding a new line manually to EACH vhost entry on EACH server! whoa....scary...


#!/bin/bash

exec < sites.txt
while read site ; do
echo "processing $site..."
awk '{print $0} '"/Alias.+reports.+\/$site"$/'{print " Alias /newalias /mnt/www/'"$site"'"}' httpd.conf > newhttpd.conf && mv newhttpd.conf httpd.conf
echo "done!"
done


Shell Scripting to Read Data From a File

Okay, so here's your problem: you have a file that contains data that you'd like to parse through a script. It's a lot of data and you don't want to sit there and continuously do the same thing over and over!

The data can be set up as one long column of data or multiple columns of data. In this case for simplicity I'll only use one column of data.

So let's say your data file is as follows:

dog
cat
cow
...
...
(long list of data)


These represent parts of filenames that you need to clear out. You don't want to sit there typing cat /dev/null > dog
cat /dev/null > cat
... So you come up with a master plan to script the process. The script will be short, sweet, and absolutely time saving!

You first need to read in the file; so this line does the work for you: exec < files.txt. Obviously, in this example my "files.txt" is the filename that contains the data I want to read. After you've opened up the file for reading, you can now parse through the file with a while loop:
while read file ; do
[do some work here]
done


Now note, "file" is the variable that we're assigning to the column. You can call the variable whatever you want. Also remember that I am being simple with this example and only have one column of data. If I wanted to do multiple columns of data, I would just assign more variables to each column. e.g. while read col01 col02 col03 ; do where $col01, $col02, and $col03 will be my new variables.

That's it! I'll leave the customization to you. Cheers!

Here is the full script example:
#!/usr/bin/bash

exec < files.txt

while read file ; do
if [ -s /mnt/$file ] ; then
cat /dev/null > /mnt/www/vdir/z/ec/$file
else
echo "/mnt/$file already empty!"
fi
done