Lex & Yacc installation in Ubuntu

To install Lex tool, type the following command in terminal:
sudo apt-get install flex
To install Yacc tool, type the following command in terminal:
sudo apt-get install bison
If the servers of bison are down and give errors, you can use
any of the following alternatives commands:
sudo apt-get install byacc
sudo apt-get install bison++
sudo apt-get install byacc j