Shell Programming and Scripting

Hi All,

I have a dhcpd.conf file that gets static hosts added and removed via a shell script. After sometime, there becomes huge gaps of space ( blank lines ) between each host block. I tried a couple of sed one-liners; but, I can't seem to get the output I'm looking for. Also, I would like to delete the blank lines between the host blocks interactively instead of piping to a file then doing a move back to the original file. Below is the output I'm looking for:

old dhcpd.conf:

host example1 {
hardware ethernet 00:00:00:00:00:01;
fixed-address 192.168.135.2;
option subnet-mask 255.255.255.0;
option routers 192.168.135.1;
next-server 192.168.135.210;
filename "linux-install/pxelinux.0";
}


host example2 {
hardware ethernet 00:00:00:00:00:02;
fixed-address 192.168.135.3;
option subnet-mask 255.255.255.0;
option routers 192.168.135.1;
next-server 192.168.135.210;
filename "linux-install/pxelinux.0";
}

host example3 {
hardware ethernet 00:00:00:00:00:03;
fixed-address 192.168.135.4;
option subnet-mask 255.255.255.0;
option routers 192.168.135.1;
next-server 192.168.135.210;
filename "linux-install/pxelinux.0";
}



new dhcpd.conf file:

host example1 {
hardware ethernet 00:00:00:00:00:01;
fixed-address 192.168.135.2;
option subnet-mask 255.255.255.0;
option routers 192.168.135.1;
next-server 192.168.135.210;
filename "linux-install/pxelinux.0";
}
host example2 {
hardware ethernet 00:00:00:00:00:02;
fixed-address 192.168.135.3;
option subnet-mask 255.255.255.0;
option routers 192.168.135.1;
next-server 192.168.135.210;
filename "linux-install/pxelinux.0";
}
host example3 {
hardware ethernet 00:00:00:00:00:03;
fixed-address 192.168.135.4;
option subnet-mask 255.255.255.0;
option routers 192.168.135.1;
next-server 192.168.135.210;
filename "linux-install/pxelinux.0";
}


Any help would be greatly appreciated. Thanks in advance!

> cat file63
host example1 {
hardware ethernet 00:00:00:00:00:01;
fixed-address 192.168.135.2;
option subnet-mask 255.255.255.0;
option routers 192.168.135.1;
next-server 192.168.135.210;
filename "linux-install/pxelinux.0";
}


host example2 {
hardware ethernet 00:00:00:00:00:02;
fixed-address 192.168.135.3;
option subnet-mask 255.255.255.0;
option routers 192.168.135.1;
next-server 192.168.135.210;
filename "linux-install/pxelinux.0";
}

host example3 {
hardware ethernet 00:00:00:00:00:03;
fixed-address 192.168.135.4;
option subnet-mask 255.255.255.0;
option routers 192.168.135.1;
next-server 192.168.135.210;
filename "linux-install/pxelinux.0";
}




> cat file63 | tr -s "\n" >file63x ; cp file63x file63 ; rm file63x
> cat file63
host example1 {
hardware ethernet 00:00:00:00:00:01;
fixed-address 192.168.135.2;
option subnet-mask 255.255.255.0;
option routers 192.168.135.1;
next-server 192.168.135.210;
filename "linux-install/pxelinux.0";
}
host example2 {
hardware ethernet 00:00:00:00:00:02;
fixed-address 192.168.135.3;
option subnet-mask 255.255.255.0;
option routers 192.168.135.1;
next-server 192.168.135.210;
filename "linux-install/pxelinux.0";
}
host example3 {
hardware ethernet 00:00:00:00:00:03;
fixed-address 192.168.135.4;
option subnet-mask 255.255.255.0;
option routers 192.168.135.1;
next-server 192.168.135.210;
filename "linux-install/pxelinux.0";
}

If you want to skip the blanc lines within the blocks:

Code:

awk '$0~/{/{f=0} $0~/}/{f=1} f&&!NF{next}1' file > file.tmp && mv file.tmp file

Both solutions remove the blank lines; however, Joeyg's example removes all blank lines. I just need to match the dhcp host blocks then reove blank lines.

Franklin52's example removes all the blank lines; but, the example first needs to read in the file, copy the output to a new file, then move the new file back to the original.

Any SED gurus have an interactive example? Meaning make the changes take place without piping the output to a new file.

I can copy the host blocks to holding buffer and delete; but, I can not copy them back correctly from the holding buffer. Here is what I got so far:


sed -e '/host/,/}/{h; d;}' -e '/$/{G;}' dhcpd.conf



The above command appends the "}" to the end of the file, not the whole host block. Also, it is not doing it interactively. I tried adding the -i option. It didn't work.

If Perl is acceptable:

Code:

perl -i~ -ne'print if /{/../}/' dhcpd.conf

You may try the same with sed but you need an implementation that supports the i option:

Code:

sed -i~ -n '/{/,/}/p' dhcpd.conf