Is replacing a particular line in a file through a bash script possible in VIM or EX?

Question

I would like to modify a particular line, say line 5, in a file by using the EOEX construct how can I achieve my aim? The code snippet that I use to achieve my purpose is as follows:

#!/bin/bash
S=0.030
F=0.150
N=30
DIFF=`echo "scale=3; $F - $S" | bc -l`
dw=`echo "scale=3; $DIFF / $N" | bc -l`
is=`echo "scale=3; $S / $dw" | bc -l`
if=`echo "scale=3; $F / $dw" | bc -l`
ex ~/Desktop/Dropbox/MATLAB/FFT.m  <<EOEX
  :5s/for*/for i = $S:$dw:$F/g
  :x
EOEX

I did some researh and learned that usually EOF(end of file) is used in here scripts for I/O redirection to the standard input of a particular command(in my case it is ex). I also learned that as long as the starting and finishing keywords are the same any word can be used instead of the EOF. My problem is that instead of the desired effect which is replacing the line with another for loop initializer in Matlab this script does not delete the line and append the string at the end of the fifth line. For reference purposes I have also added my FFT.m file. I apologize for the inconvenience caused by the abstractedness of my question previously. Note that I am also open to using another program to achieve the desired effect but curious about why it cannot be achieved in ex or vim. Please click here for the Matlab script.

Answer 1

To change line 5 of a file called test_file to 'hello world' using ex and the EOEX construct (by which I presume that what you mean is a 'here document'):

ex test_file << EOEX
5c
hello world
.
wq
EOEX

The above is also possible with ed, although note that POSIX ed doesn't support the wq command. Instead put the w and q on separate lines.

Using sed (a version that supports the -i option) is a bit simpler:

sed -i '15 c hello world' test_file