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Want to delete few lines above and below certain string ( sed / awk )

My requirement is to delete certain lines from my nagios file, might be you have some different requirement but the agenda remains the same.



Lets take an example.

Below mentioned is a part of my hostname.cfg file.

My requiremnet is to make a shell script to delete lines begining from "define host {" upto "}"
and the variable input ( read ) to fetch from user is just the host_name which can differ.

here i want to delete all entries relevant to host_name --> hostname02x
so i need to delete entries relevant to it beginning from "define host {" upto "}" , so that the file which earlier look

#cat hostname.cfg

define host{
                use                     linux-server            ; Name of host template to use
                host_name               hostname01x
                hostgroups              COT-Servers
                contact_groups          admins
                alias                   FEA Preprod
             }

define host{
                use                     linux-server            ; Name of host template to use
                host_name               hostname02x
                hostgroups              COT-Servers
                contact_groups          admins
                alias                   Grid Engine
              }

looks like...

#cat hostname.cfg

define host{
                use                     linux-server            ; Name of host template to use
                host_name               hostname01x
                hostgroups              COT-Servers
                contact_groups          admins
                alias                   FEA Preprod
             }


Sed Method 


# sed -i.bak '/define host/ {:a;/}/!{N;ba};/hostname02x/d}' hostname.cfg


Explanation :

  • /define host/ : starting from /define host/
  • :a : a label for upcoming loop
  • /}/! : if } is not found...
  • N : append the line to the pattern space
  • ba : branch to label a to check if next line contains a }
  • when loop ends, } has been found
  • /hostname02x/d : deletes the pattern space if it matches /hostname02x/

Awk Method


awk -v RS="[}]\n" -v ORS="}\n" '!/hostname02x/' hostname.cfg


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