field.c

/* 1987 (c) Stephen R. Bourne (from the Unix system V Environment).
 * I have been true to the style, except for adding typedeclarations in order
 * for it to compile without warnings on gcc (-std90?) without warnings.
 * McUsr 14.05.2023
 */

#include <stdio.h>

#define MAXF 256


#define MAXL 4096
#define IFS '\t'
#define OFS '\t'

int fv[MAXF] ;      /* numerical equivalent of arguments. */
int nf ;            /* number of columns to print */
int mf;             /* number of fields in current record */ 

char *fp[MAXF];     /* pointers into 'L' at field boundaries */
char L[MAXL];       /* current line buffer */

void putf( int n);

int main(int argc, char **argv )
{
    register char *cp;
    register char **ap;
    register int c;
    int f;

    /* read arguments into fv[...] */

    while (argc>1) {
        if(sscanf(argv[1],"%d", &fv[nf++]) != 1 ){
            printf("usage: field [ n ] ...\n") ;
            return(2);
        }
        argc--; argv++ ;
    }
    /* read and copy input */
    nf--;
    cp = L;
    ap = fp;
    *ap++ = cp ;
    while(1) {
        c = getc(stdin) ;
        if(c=='\n' || c==EOF ) {
            int fc;
            if(cp==L && c==EOF ) break;
            *cp++ = 0;
            mf = ap-fp;

            /* print this line */
            for(fc = 0; fc <= nf; fc++) {
                putf(fv[fc]-1);
                if(fc != nf) putchar(OFS) ;
            }
            if(c == EOF) break ;
            putchar('\n');
            cp = L ;
            ap = fp ;
            *ap++ = cp ;
        }
        else if(c == IFS) {
            *cp++ = 0 ;
            *ap++ = cp;
        }
        else *cp++ = c;
    }
    return (0);
} /* main */

/* output field n from the current line */
void putf( int n) 
{
    register char *cp = fp[n] ;
    register char c;
    if(n<0 || n >=mf) return ;
    while(c = *cp++) putchar(c) ;
}