How to search and replace in multiple files

In Mac OSX, recursively using sed, from foo into bar:

find . -type f -exec sed -i '' -e 's/foo/bar/g' {} \;

How to convert Japanese character set to UTF-8

Using iconv, try one of these below:

iconv -f SHIFT-JIS -t UTF-8 input_file.txt > output_file.txt

or

iconv -f ISO-2022-JP -t UTF-8 input_file.txt > output_file.txt