$ cat mysrc/realpath.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>

int main( int argc, char **argv ){
        char    buf[PATH_MAX+1];
        char    obuf[PATH_MAX+1];
        char    *bp ;
        char    *cp ;
        int     i = 1 ;
        int     both = 0 ;
        int     cmdl = 0 ;

        /* Process any arguments or offer help */

        while ( i < argc
             && argv[i][0] == '-' ){
                if ( !strcmp( argv[i], "-b" )){
                        both = 1 ;
                        i++ ;
                        continue ;
                 }
                if ( !strcmp( argv[i], "-f" )){
                        cmdl = 1 ;
                        i++ ;
                        break ; /* files beginning with - are made legal */
                }
                fputs(
"\n"
"Usage: realpath [ -b ] [ -f ] [ <file_name_1> . . . .<file_name_N> ]\n"
"\n"
"Calls function realpath() to get a no-symbolic-link absolute path for each\n"
"<file_name> and prints them to standard output.  File names can be provided\n"
"as lines on standard input or as command line arguments.  If -f is not\n"
"present, the first argument not starting with a '-' is the start of the file\n"
"list.\n"
"\n"
"The -b argument causes realpath to prefix each output line with the input\n"
"file name and a tab character.\n"
"\n"
"The -f argument causes realpath to interpret all following arguments as\n"
"file names, even if the first starts with '-', and if no arguments follow.\n"
"When -f is present, realpath does not read file names from standard input.\n"
"\n", stderr );
                exit ( 1 );
         }

        if ( !cmdl
          && i < argc ){
                cmdl = 1 ;
         }

        while (
            (  cmdl
            && i < argc
            && ( bp = argv[i++] ))
          ||
            (  !cmdl
            && ( bp = fgets( buf, sizeof( buf ), stdin )))
          ){
                if ( cp = strchr( bp, '\n' )){
                        *cp = NULL ;
                 }

                if ( !realpath( bp, obuf )){
                        fflush( stdout );
                        fputs( "realpath() failure: ", stderr );
                        perror( bp );
                        continue ;
                 }

                if ( ( both
                    && 0 > printf( "%s\t", bp ))
                  || 0 > printf( "%s\n", obuf )){
                        if ( ferror( stdout )){
                                perror( "stdout" );
                                exit( 1 );
                         }

                        exit( 0 );
                 }
         } /* end while args or stdin */

        if ( ferror( stdin )){
                fflush( stdout );
                perror( "stdin" );
                exit( 1 );
         }

        exit( 0 );
 } /* end main () */