PT[101]% ls
ch2-01.l	ch2-01.txt	hello.txt	hello.l
PT[102]% flex ch2-01.l
PT[103]% gcc lex.yy.c -ll
PT[104]% ./a.out
hello
hello3
number
3.14
number
-0.314159E+01
number
abc123xyz
abcnumber
xyz^C
PT[105]%