How to insert text after a block of text?

Shell Programming and Scripting
1

Input:

fstab is a configuration 
file that contains information 
of all the partitions 

and storage devices 
in your computer. 

The file is located under /etc, 
so the full path 
to this file is /etc/fstab.

The >>>>> characters would be replaced by some texts.
For example if i run a shell script,

./run.sh sometexts infile

Output would be:

fstab is a configuration 
file that contains information 
of all the partitions 
sometexts

and storage devices 
in your computer.

The file is located under /etc, 
so the full path 
to this file is /etc/fstab.
2

Using sed to replace the >> character

#!/bin/ksh
#save file as run.ksh

sed "s/>>*/$1/g" $2 > outfile
3 
$ cat run.sh 
perl -pi -e s"/>>>>>>>>/$1/" $2

./run.sh sometexts infile
4

something like this:

run.sh

#!/bin/bash
sed -e "s/^>>>*/$1/" $2

run as:

run.sh hellohello infile
5

There is no >>>>> characters in input file,the >>>> means the position.
Input:

fstab is a configuration 
file that contains information 
of all the partitions 

and storage devices 
in your computer. 

The file is located under /etc, 
so the full path 
to this file is /etc/fstab.

Insert texts after first block of texts.

6 
$ cat run.sh 
perl -pi -e s"/partitions/partitions\n$1/" $2

./run.sh sometexts infile