#!/usr/local/bin/fontforge
# Quick and dirty hack: converts a font to truetype (.ttf)
Print("Opening "+$1);
Open($1);
Print("Saving "+$1:r+".ttf");
Generate($1:r+".ttf");
Quit(0);

http://www.stuermer.ch/blog/convert-otf-to-ttf-font-on-ubuntu.html

Save the script as otf2ttf.sh and type:

fontforge -script otf2ttf.sh FONTNAME.otf

If you want to convert many .otf fonts in a directory to .ttf fonts, type (thanks sw!):

for i in *.otf; do fontforge -script otf2ttf.sh $i; done

Convert otf to ttf

Bash