If you use the _s starter theme from automattic you can enter these commands to replace _s with your theme name

gistfile1.sh

# Search for:'_s', Replace with:'yourthemename' (text domain)
find . -type f \( -iname "*.php" -o -iname "*.css" -o -iname "*.txt" \) -exec sed -i "" "s/\'_s\'/\'yourthemename\'/g" '{}' \;

# Search for:_s_, Replace with:yourthemename_ (function names)
find . -type f \( -iname "*.php" -o -iname "*.css" -o -iname "*.txt" \) -exec sed -i "" "s/_s_/yourthemename_/g" '{}' \;

# Search for: _s, Replace with: Yourthemename (in comments)
find . -type f \( -iname "*.php" -o -iname "*.css" -o -iname "*.txt" \) -exec sed -i "" "s/ _s/ Yourthemename/g" '{}' \;
# Don't remove the space in ' Yourthemename'

The _s starter theme is located on Github https://github.com/Automattic/_s