Cat a File, Without the Comments

I recently had to install a couple of squid servers to act as reverse proxies for a webcluster. You can teach the squid server to stand in between in the end users and the webservers, and to store all the static content ( .jpg .flv .css .htm for example ) in the RAM. This saves a lot of I/O and bandwidth on the webservers, and it can really speed up a site. At the end of the road the webservers' load dropped by 92%. But before all this worked, I had to run through a massive config file and since the squid config file is their manual at the same time, it's about 5000 lines long. So I had to find out a way to filter only the important settings from the config file.

This is what I came up with:

$ cat /etc/squid/squid.conf | egrep -v "(^#.*|^$)"

Explained

egrep -v      means leave the following out
^#.*          means patterns that begin with a #
|             means or
^$            means patterns that are empty

Updates

update #1

Thanks to an insightful comment by Darwin Award Winner on this article, here's a version that would also filter comments with spaces before the #, such as comments that are indented with code blocks:

$ cat /etc/squid/squid.conf | egrep -v "^\s*(#|$)"

Thanks Darwin! :wink:

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Legacy Comments (8)

These comments were imported from the previous blog system (Disqus).

Darwin Award Winner·Jul 31, 2007

I would suggest \"^\\s*(#|$)\" as the pattern, since this would also filter comments with spaces before the #, such as comments that are indented with code blocks.

If you also wanted to remove comments at the ends of lines, you could pipe the output through sed \'s/\\s+#.*$//\'

cat /etc/squid/squid.conf | egrep -v \"^\\s*(#|$)\" | sed -e \'s/\\s+#.*$//\'

You could create a script /usr/local/bin/conconf (catconf as in cat config files, or make up a more creative name) with the following contents (remember to make it executable):

#!/bin/sh
cat \"$@\" | egrep -v \"^\\s*(#|$)\" | sed -e \'s/\\s+#.*$//\'

Kevin·Jul 31, 2007

@Darwin Award Winner: Those are great suggestions, thanks! I will update the article.

aptgetupdate.de·Jul 31, 2007

Thanks.

Bash·Mar 17, 2009

Useless use of cat award!

http://sial.org/howto/shell...

Kev van Zonneveld·Mar 19, 2009

@ Bash: Point taken. Though there are two points to be made as well:

- The consistent use of cat can be a good habit to ensure you never modify a file by accident.
- I doubt the extra process will have serious impact on my machine\'s performance. If it does, it\'s time for a new machine :)

jumbe·Dec 22, 2010

Thanks for this man.

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