Talk

Short simple scripts

Every now and then I get to write some scripts to fetch the required data from a file. These days I'm having to deal with the Sybase interfaces file. I need to translate from a server name to the host and port.

This file can be large and the format is of the form:

SERVER
query tcp ether host1 1234
master tcp ether host1 1234

Grepping with a multi-line regex can be a pain. So here is one solution:

awk '/SERVER/{f=1}f>0{f++};f>2{print$4" "$5;exit}' interfaces

Wait. On Sun systems Sybase sometimes uses TLI for the host/port so the file can look like this:

SERVER
query tli /dev/tcp \x000208fca60e123f0000000000000000
master tli /dev/tcp \x000208fca60e123f0000000000000000

The following awk script can handle this case:

awk '/SERVEr/{f=1}f>0{f++}f>2{ if($2=="tli") print $5; else print $4:; exit}' $SYBASE/interfaces

Finally we need to convert back from the TLI format to host/port. Here is some javascript that can do that (assuming val has the string).

port = parseInt(val.substring(2,6),16);
host = parseInt(val.substring(6,8),16)
+"."+parseInt(val.substring(8,10),16)+"." + parseInt(val.substring(10,12),16)+"." + parseInt(val.substring(12,14),16);
print ("host "+host+" port "+port);

And if you decide you want to filter crontab files for a certain program here is something:

crontab -l | sed -n -e '/^#/d' -e '/string/p' | awk '{print $6}'

References:
sed FAQ, version 014
Awk reference