Need Lex regular expression to match string upto newline

Question

I want to parse strings of the type :

a=some value
b=some other value

There are no blanks around '=' and values extend up to newline. There may be leading spaces.

My lex specification (relevant part) is:

%%  
a=  { printf("Found attr %s\n", yytext); return aATTR; }
^[ \r\t]+   { printf("Found space at the start %s\n", yytext); }
([^a-z]=).*$  { printf("Found value %s\n", yytext); }
\n  { return NEWLINE; }
%%

I tried .*$ [^\n]* and a few other regular expressions but to no avail. This looks pretty simple. Any suggestions? I am also aware that lex returns the longest match so that complicates it further. I get the whole line matched for some regular expressions I tried.

mevets mevets · Accepted Answer · 2019-01-17T18:10:11

You probably want to incorporate separate start states. These permit you to encode simple contexts. The simple example below captures your id, operator and value on each call to yylex().

%{
char id;
char op;
char *value;
%}

%x VAL OP
%%
<INITIAL>[a-z]+ {
    id = yytext[0];
    yyleng = 0;
    BEGIN OP;
}
<INITIAL,OP>[ \t]*
<OP>=[ \t]* {
    op = yytext[0];
    yyleng = 0;
    BEGIN VAL;
}
<VAL>.*\n {
    value = yytext;
    BEGIN INITIAL;
    return 1;
}
%%

Need Lex regular expression to match string upto newline

1 Answers