sed append text after N-th occurrence

Question

I have a template of the following script and I need to insert the different PARAM value for each case.

case $1 in
1)
    export PARAM=
    ;;
2)
    export PARAM=
    ;;
3)
    export PARAM=
    ;;
esac

I just found an example how to insert the value for the 1st case PARAM:

sed -i '/export PARAM=/{s//export PARAM=1212212121/;:a;n;ba}' file

but how can I do this for cases 2 and 3?

Answer 1

Use awk:

awk -v v="1212212121" -v n=2 '/Param/{c++} c==n-1{$(NF)+=" "v}1' file
awk -v v="1212212333" -v n=3 '/Param/{c++} c==n-1{$(NF)+=" "v}1' file

and so on...

Explanation:

• /Param/{c++} increments a counter c every time the pattern /Param/ is found.
• c==n-1 checks if c has the desired value and adds the value add the
• 1 is always true. awk will print all lines.
• -v v="1212212121" -v n=2 passes the variables v and n to the script.

Answer 2

This might work for you (GNU sed):

n=2 v=11212212121
sed -ri '/export PARAM=/{x;s/^/x/;/x{'$n'}/!{x;b};x;s/(export PARAM=).*/\1'$v'/;:a;n;ba}' file

Keep a counter in the hold space and if the counter matches your expectation, substitute and then print out the remainder of the file.