%{
#include
#include
int ln=1;
%}
%%
"\n" {}
.*hello.* {fprintf(yyout,"\n%d:%s",ln++,yytext);}
.* {ln++;}
%%
main()
{
yyin=fopen("try1.txt","r");
yyout=fopen("try2.txt","w");
yylex();
return 0;
}
int yywrap()
{
}
Sample output
try1.txt
hai
hello world
test file
language processor
hello
try2.txt
2:hello world
5:hello