Let's suppose, you want to find string ${STRING} in file ${FILE}
Run mcview application
# mcview ${FILE}
In mcview window push F7 and enter criteria for search - string ${STRING}.
For next search enter F7 again.
To go to end of file press SHIFT+G.
To search from the end of file to beginning use corresponding option "Backwards" in F7 window.
To exit from mcview press F10 or 2 times ESC.
In case if file has become too big it would be too long to search something in it.
Then purge it with command:
# dd if=/dev/null of=${FILE}