安装php出现错误！！

错误如下：
[root@sjf php-4.3.4]# ./configure --prefix=/usr/local/php --with-apxs=/usr/local/apache/bin/apxs --with-config-file-path=/usr/local/lib --enable-track-vars --with-xml --with-mysql



loading cache ./config.cache
checking host system type... i686-pc-linux-gnu
checking for gcc... gcc
checking whether the C compiler (gcc  ) works... yes
checking whether the C compiler (gcc  ) is a cross-compiler... no
checking whether we are using GNU C... yes
checking whether gcc accepts -g... yes
checking whether gcc and cc understand -c and -o together... yes
checking how to run the C preprocessor... gcc -E
checking for AIX... no
checking if compiler supports -R... no
checking if compiler supports -Wl,-rpath,... yes
checking for re2c... exit 0;
checking for ranlib... ranlib
checking whether ln -s works... yes
checking for gawk... gawk
checking for bison... no
checking for byacc... no
configure: warning: You will need bison if you want to regenerate the PHP parsers.
checking for flex... lex
checking for yywrap in -ll... no
checking lex output file root... ./configure: line 2425: lex: command not found
configure: error: cannot find output from lex; giving up


请问各位大侠我该怎么办？？

没有安装lex

谢谢楼上的，装了flex后问题就解决了。