Add string after a certain string in the same line in a text file

Question

I have been trying to add a string in the same line in a text file. I have used following method.

sed -i "s/\bmembers\b/& \t$host,/" printer.cfg

It will add a string after members string and also it will add tab in order to make it proper.

I will get result like this,

define hostgroup{
hostgroup_name  HOSTGROUP ONE   
alias       Host Group 1 Printers
members     foo0, foo1, bar2, foo2, bar3
}

Where foo0 is my added string using above sed.

But the problem is there is one text file, that contains many "members" string.

e.g.

define hostgroup{
hostgroup_name  HOSTGROUP ONE   
alias       Host Group 1 Printers
members     foo1, bar2, foo2, bar3
}

define hostgroup{
hostgroup_name  HOSTGROUP TWO
alias       2nd Host Group
members     example1, example3, example2
}

In this above example, I want to add string ONLY in first para (hostgroup_name HOSTGROUP ONE). In this case, How can I refer hostgroup_name and add text after "members" string with one tab?

Answer 1

Two approaches:

sed approach:

sed "0,/members/{s/\bmembers */&$host, /}" printer.cfg

• 0,/members/ - address range occupying a range of lines starting from the 1st line till the first occurrence of members pattern

---

awk approach:

awk -v h=$host '!f && /members /{ $2=sprintf("%8s, %s",h,$2); f=1 }1' printer.cfg

---

The output (for both approaches):

define hostgroup{
hostgroup_name  HOSTGROUP ONE   
alias       Host Group 1 Printers
members     foo0, foo1, bar2, foo2, bar3
}

define hostgroup{
hostgroup_name  HOSTGROUP TWO
alias       2nd Host Group
members     example1, example3, example2
}

Answer 2

Follow the 3-step process of selecting, storing, and shaping the range of interest data. The final task of printing to stdout is an autotask of sed.

host='Foo_0';
sed -Ee '

   # Step-1: SELECT RANGE
   /^define hostgroup[{]/,/^[}]/!b

   # Step-2: SAVE RANGE DATA
   H; /^define hostgroup[{]/h; /^[}]/!d

   # Step-3: SHAPE RANGE DATA
   g;/\nhostgroup_name\s+HOSTGROUP ONE/s/\nmembers\s+/&'"${host}"', /

' printer.cfg