lazysphere/command/echo.c

/**
 *  file: echo.c
 *  command: echo
 *  author: Tyler Murphy
 */

#include "command.h"
#include "lslib.h"

#include <stdlib.h>

/**
 * Flags that are to be used with echo
 */
static struct {
    bool escape_codes;
    bool newline;
} flags;

/**
 * Prints a null terminated string to standard out and changes each char based on input flags
 * @param str the string to print
 */
static void print_with_escape_codes(const char* str) {
    
    size_t index = 0; /* current index in the string */
    char c; /* current char being read */
    char n; /* next char being read */

    while (true) {
        c = str[index]; /* read current char */
        index++;

        if (c == '\0') break; /* if we hit the NUL, break */
        if (c != '\\') { /* if its not a escaped code, print and continue */
            putchar(c);
            continue;
        }

        /* read next character */
        n = str[index];
        index++;

        /* check each char against the valid escape codes */
        switch (n) {
            case '\\':
                putchar('\\');
                break;
            case 'b':
                putchar('\b');
                break;
            case 'c':
                exit(EXIT_SUCCESS);
            case 'n':
                putchar('\n');
                break;
            case 'r':
                putchar('\r');
                break;
            case 't':
                putchar('\t');
                break;
            case 'v':
                putchar('\v');
                break;
            default: /* if none found print both chars as is */
                putchar(c);
                putchar(n);
        }
    }
}

/** 
 * Takes in each argument that has a single - and parses it 
 * @param c the character after the -
 * @param next the next argument in argv that hasnt been parsed
 * @reutrn if the next arg was used or if the arg was invalid
 */
static int short_arg(char c, char* next) {
    UNUSED(next);
    switch (c) {
        case 'e':
            flags.escape_codes = true;
            break;
        case 'E':
            flags.escape_codes = false;
            break;
        case 'n':
            flags.newline = false;
            break;
        default:
            flags.newline = true;
            flags.escape_codes = false;
            return ARG_IGNORE;
    };
    return ARG_UNUSED;
}

/**
 * Prints data in each argument to stdout
 */
COMMAND(echo_main) {

    int start, i;

    /* if no arguments supplied exit */
    if (argc < 1) {
        return EXIT_FAILURE;
    }

    /* set default flags */
    flags.escape_codes = false;
    flags.newline = true;

    /* parse arguments, no help message */
    start = parse_args(argc, argv, NULL, short_arg, NULL);

    /* for each argument either print as is or parse each character for escape codes */
    for (i = start; i < argc; i++) {
         if (flags.escape_codes) {
            print_with_escape_codes(argv[i]);
        } else {
            printf("%s", argv[i]);
        }

        /* put a space seperator between arguments */
        if (i + 1 != argc) {
            putchar(' ');
        }
    } 

    /* if set to put a new line at the end (default), do so */
    if (flags.newline) {
        putchar('\n');
    }

    /* done */
    return EXIT_SUCCESS;
}