[SOLVED] Is there a C equivalent to grep?

RandomTroll · 07-12-2019, 05:18 PM

I wrote a program. The first iteration I passed every parameter on the command line. That got unwieldy as I had to add more. I'd like to have it read a configuration file instead. If it were a script, I'd just have it

Code:

BaseName=`grep -w ^BaseName ConfigurationFile | cut -d: -f2`

Is there anything more convenient than strstr?

rtmistler · 07-12-2019, 06:50 PM

Can't really tell what you're trying to do.

strstr() is fairly convenient if you know what you need it for and how to use it.

As far as other library functions, the grep page for the first one usually has a SEE ALSO section.

As far as programming convenience, once can always code string searches regardless of library use.

One can also look at the source code for each of grep and also strstr().

individual · 07-12-2019, 08:14 PM

There isn't a convenient function included with the standard library, but using existing functions you can roll your own. If you want I'll share a function that I use when I need simple pattern matching.

RandomTroll · 07-13-2019, 06:50 AM

Quote:

Originally Posted by rtmistler

Can't really tell what you're trying to do.

I want a program to read parameters from a configuration file instead of the command line. For instance I want to have a plain-text initialization file that looks like:

Quote:

Fruit: Apple
Fish: Trout
Vegetable: Asparagus

and have the program assign the value Apple to the variable Fruit...

Quote:

Originally Posted by rtmistler

One can also look at the source code for each of grep and also strstr().

Duh. I can also write it in assembly and use no libraries.

Quote:

Originally Posted by individual

There isn't a convenient function included with the standard library

It's done so often that surprises me. I found getconf and confstr, but they don't seem to apply

Quote:

Originally Posted by individual

If you want I'll share a function that I use when I need simple pattern matching.

That'd be nice. I started by fopen-ing it, reading it line-ly with getline, picking out the first word, running that through switch on all the possible variables.

Later: discovered strtok, the function perfect for separating elements on a line.

individual · 07-13-2019, 10:05 AM

EDIT: Solved, I guess?

RandomTroll · 07-13-2019, 04:19 PM

Yes. It would have been nice to have a switch that worked on strings, but a cascade of else ifs isn't awful. If I were really serious I'd convert to a database and query that.

RandomTroll · 07-13-2019, 09:17 PM

Useful note: fgets, getline, etc., emit the newline with the last token on the line. That took a while to figure out and strip out.

WideOpenSkies · 07-13-2019, 09:56 PM

Quote:

Originally Posted by RandomTroll

Useful note: fgets, getline, etc., emit the newline with the last token on the line. That took a while to figure out and strip out.

getline is only on C++, no? If so, that might not count because OP is specifically asking about C.

individual · 07-13-2019, 10:08 PM

Quote:

Originally Posted by Contrapak

getline is only on C++, no? If so, that might not count because OP is specifically asking about C.

RandomTroll is the OP.

There is a C++ version of getline, but getline is part of POSIX. From the man page:

Quote:

Both getline() and getdelim() were originally GNU extensions. They were standardized in POSIX.1-2008.

Mechanikx · 07-13-2019, 11:11 PM

Quote:

Originally Posted by RandomTroll

Useful note: fgets, getline, etc., emit the newline with the last token on the line. That took a while to figure out and strip out.

In one of my C books I'm studying the author provides his own function for testing for the newline and removing it if it's been read by fgets().

I'll post his solution in case you might find it useful.

Code:

char *s_gets(char *st, int n)
{
    char *ret_val;
    char *find;

    ret_val = fgets(st, n, stdin);
    if (ret_val)
    {
        find = strchr(st, '\n');    /* look for newline */
        if (find)                   /* if the address is not null... */
            *find = '\0';           /* ...place a null character there */
        else
            while (getchar() != '\n')    /* dispose of rest of line */
                continue;
    }
    return ret_val;
}

ehartman · 07-13-2019, 11:13 PM

Quote:

Originally Posted by individual

There isn't a convenient function included with the standard library, but using existing functions you can roll your own. If you want I'll share a function that I use when I need simple pattern matching.

To get more grep-like behaviour, you can use the functions contained in the pcre(3) library

Quote:

The PCRE library is a set of functions that implement regular expression pattern matching using the same syntax and semantics as Perl, with just a few differences.
Some features that appeared in Python and PCRE before they appeared in Perl are also available using the Python syntax, there is some support for one or two .NET and Oniguruma syntax items, and there is an option for requesting some minor changes that give better JavaScript compatibility.

This probably goes much further then what the OP requested, but it is a possible answer to the subject.

RandomTroll · 07-14-2019, 12:35 PM

I've already written the program in C. I used strcspn to reject newlines.