Install Flex by running the following commands: ./configure --prefix=/usr && make && make install Some programs don't know about flex and try to find the lex program (flex is a (better) alternative for lex). So to please those few programs out there we'll create a bash script called lex that calls flex and have it emulate lex. Create a new file /usr/bin/lex by running the following: cat > /usr/bin/lex << "EOF" #!/bin/sh # Begin /usr/bin/lex exec /usr/bin/flex -l "$@" # End /usr/bin/lex EOF chmod 755 /usr/bin/lex