Changing a line in a text file with bash..?

[Eric_T]

Hello

I have a fortran program that reads an input file and then does a bunch of computations based on that file. What I want to do is to write a script to change some of the variables, say run the program 10 times and each time increment the variable input_velocity in file input.txt by 10. I know how to make all the parts except how to change that one line. I know several ways of finding it, like grep input_velocity input.txt and awk '/input_velocity/' input.txt, but that doesn't help me much.. ](*,)
Could anyone give me some tips?

Thanks!

[Eric_T]

Heh, figured out one way to do it...

perl -pi -e 's/input_velocity = ".*"/input_velocity = "somethingelse"/' input.txt

But if anyone have another way to do it, it would be great to hear from you!

[23meg]

You can also use ed and sed.

[Eric_T]

You can also use ed and sed.

Yep, like this:

sed -i 's/input_velocity = .*/input_velocity = 200/' input.txt

[schkovich]

In case you need to assign to input_velocity value from variable then you might do:


speed=314
replacement=s/input_velocity = .*/input_velocity = ${speed}/
sed -i $replacement input.txt

[frenchn00b]

awk does also the job:

http://www.sunsite.ualberta.ca/Documentation/Gnu/gawk-3.1.0/html_chapter/gawk.html