DNS query script

timmeke · 07-05-2006, 02:38 AM

grep searches lines that matches a certain pattern or regular expression and returns the lines matched.
grep -E (or egrep) uses Extended Regular Expressions for the matching.
In short, the reg. expression
'W\.X\.Y\.Z\.$'
matches all lines ending on ('$' at the end) "W.X.Y.Z." (ie host outputs '<host or domain> mail is handled by <DNS priority> <server>'
The backslash before the '.' is an escape character that avoids having '.' interpreted as 'any random character'.

sed, short for stream editor, manipulates a stream line-by-line.
The sed command I used above does the following:
-e tells sed that the next argument is a editing command.
's/abc/def/' : is a command to substitute (hence the "s" in front) the pattern "abc" by "def" in each line and outputs the result. If "abc" isn't found in the input line, the line is outputted without change.
The patterns can be strings, regular expressions or a combination of both.

Whereas grep is for line-based searching, cut is more for byte/column searching.
For instance,
cut -d' ' -f7 says:
Split up the lines, based on the ' ' (space) as delimiter (-d option) and output only the 7th field (-f7).
You can also ask for ranges of fields (ie -f1-6 (=from first to sixth field) or -f2- (=from 2nd field to the end of the line)).

Personnally, I would recommend reading up on regular expressions. They can be a little difficult and cryptic at first, but they are commonly used.

Check out also the information on tldp.org (the linux documentation project), the tutorials/how-to's on this site and maybe also linux.about.com.

Braynid · 07-05-2006, 05:35 AM

Okie so this is sord of the final version, i've dropped the idea to verify the NS, i'll just do it myself with 'dig -t NS $1 +short' if it's the right one i'll know.

Code:

function dns ()
{
####################################
echo "                             "
echo DNS resolve:
echo "                             "
dig +nocmd +nostats +nocomments +noquestion $1
echo "                             "
echo Inregistrari MX:
echo "                             "
host -t mx $1
echo "                             "
echo "Sunt folosite urmatoarele NS-uri:"
echo "                             "
dig -t NS $1 +short
echo "                             "
####################################
}

Guys thanks for all the kind support. Be good!

@timmeke the information you give there makes me think of adding some improvements to my script, thanks a million times!

timmeke · 07-05-2006, 05:45 AM

You're very welcome, Braynid.