Grepping out comments and blank lines

One thing we commonly see in open-source configs is an abundance of helpful comments. Often, they dwarf the number of active parameters being set and that can make things very hard to read.

In the blessed world of unix, there is an easy solution to this: you simply use grep to remove those lines from a listing of the contents of the file.

First, grep out the comments:

grep -v \# file

Usually, that will leave you with a lot of unnecessary whitespace, as well. So just pipe that output through an enhanced grep and filter for blank lines:

grep -v \# file | egrep -v "^$"

To clarify the above, here's a break down of each component:

grep - self explanatory

-v - tells grep to remove what matches rather than show it

\ - tells the shell the special character # is to be passed to the process without interpretation

# - the near-universal symbol for "comment" in config-ese

file - a stand in for whatever conf you're digging through

| - a pipe. Tells the shell to send the output of what's to the left of the pipe to what's on its right

egrep - grep with extended regular expressions (a sophisticated text manipulation language)

-v - telling egrep to remove the matches

"" - passing what's inside to grep without shell interpretation

^ - Means "the start of the line"

$ - Means "the end of the line"

So what you're telling it, in essence, is the following:

1. Read the contents of file
2. Remove all lines with "#"
3. Pass the result to egrep
4. Egrep: remove all lines which begin and immediately end (ie, a blank line) and output the result

This is one of those little tricks that goes a long way to simplifying interactions with Unix hosts and it's actually the first thing I do when I go to read any new service's default config.

Hope it helps.