how to modify a file php

hi there I am trying to modify a text file i am using PHP or also i can use the C# the file that i am working on a text file consists of strings for example

TM_len= -------------------------------------------- EMM_len -------------------------------------------- T_len=45 CTGCCTGAGCTCGTCCCCTGGATGTCCGGGTCTCCCCAGGCGG NM_=2493 ----------------ATATAAAAAGATCTGTCTGGGGCCGAA and i want to delete those four lines from the file if i found that one line consists of only "-" no characters in it and of course save to the file. any help please ??