install problem with "flex" ?? please help

Hi All, I try to install php-4 on a linuxBox with apache-1.3.6 and perl 5.0 and I get following error: ***************** configure:2146: checking whether ln -s works configure:2173: checking for flex configure:2173: checking for lex configure:2206: checking for flex configure:2240: checking for yywrap in -ll configure:2259: gcc -o conftest -g -O2 conftest.c -ll 1>&5 /usr/i486-linux/bin/ld: cannot open -ll: No such file or directory collect2: ld returned 1 exit status configure: failed program was: #line 2248 "configure" #include "confdefs.h" /* Override any gcc2 internal prototype to avoid an error. */ /* We use char because int might match the return type of a gcc2 builtin and then its argument prototype would still apply. */ char yywrap(); int main() { yywrap() ; return 0; } configure:2282: checking lex output file root **************** what is Flex ? Thank you in advance Ronald Weinrich