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Top Forums Programming Unix Shell background processing Post 302457313 by Corona688 on Monday 27th of September 2010 06:08:21 PM
Old 09-27-2010
[edit] hang on

---------- Post updated at 04:04 PM ---------- Previous update was at 04:00 PM ----------

It could be crashing because you don't necessarily have 20 arguments. in which case you'll be feeding strcmp either garbage or NULL, either of which would cause it to crash. You'll need to remember how many arguments parseargs found(maybe put it through its return value instead of 'void'?)

In any case I don't think strcmp will do what you want. It returns 0 when the two strings are exactly the same, meaning, it'll only match on a line with no newlines containing nothing but &. I think you want strstr or strchr instead, see their man pages.

---------- Post updated at 04:08 PM ---------- Previous update was at 04:04 PM ----------

Code:
    switch(pid)
    {
        case -1:  
            cout << "DEBUG:Fork Failure" << endl;
            exit(-1);
            break;

        case  0:
            execvp(cmd[0], cmd);
            
            if(execvp(cmd[0], cmd) == -1)
            {
                cout << "Command Not Found" << endl;
                exit(0);
            }
            break;
   
        default:  
            wait(NULL);
            cout << "DEBUG:Child Finished" << endl;
            break;
    }

I'm surprised this even compiled, a break in the default section is mandatory in some common compilers.

Imagine case 0 without the break. If execvp() fails and doesn't catch the error it might keep going, and print "DEBUG: child finished" because the case statements don't tell it where to end, just where to begin. But with the break, it will leave that section of code entirely like you expected it to do.
 

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OD(1)									FSF								     OD(1)

NAME
od - dump files in octal and other formats SYNOPSIS
od [OPTION]... [FILE]... od --traditional [FILE] [[+]OFFSET [[+]LABEL]] DESCRIPTION
Write an unambiguous representation, octal bytes by default, of FILE to standard output. With more than one FILE argument, concatenate them in the listed order to form the input. With no FILE, or when FILE is -, read standard input. All arguments to long options are mandatory for short options. -A, --address-radix=RADIX decide how file offsets are printed -j, --skip-bytes=BYTES skip BYTES input bytes first -N, --read-bytes=BYTES limit dump to BYTES input bytes -s, --strings[=BYTES] output strings of at least BYTES graphic chars -t, --format=TYPE select output format or formats -v, --output-duplicates do not use * to mark line suppression -w, --width[=BYTES] output BYTES bytes per output line --traditional accept arguments in traditional form --help display this help and exit --version output version information and exit Traditional format specifications may be intermixed; they accumulate: -a same as -t a, select named characters -b same as -t oC, select octal bytes -c same as -t c, select ASCII characters or backslash escapes -d same as -t u2, select unsigned decimal shorts -f same as -t fF, select floats -h same as -t x2, select hexadecimal shorts -i same as -t d2, select decimal shorts -l same as -t d4, select decimal longs -o same as -t o2, select octal shorts -x same as -t x2, select hexadecimal shorts For older syntax (second call format), OFFSET means -j OFFSET. LABEL is the pseudo-address at first byte printed, incremented when dump is progressing. For OFFSET and LABEL, a 0x or 0X prefix indicates hexadecimal, suffixes may be . for octal and b for multiply by 512. TYPE is made up of one or more of these specifications: a named character c ASCII character or backslash escape d[SIZE] signed decimal, SIZE bytes per integer f[SIZE] floating point, SIZE bytes per integer o[SIZE] octal, SIZE bytes per integer u[SIZE] unsigned decimal, SIZE bytes per integer x[SIZE] hexadecimal, SIZE bytes per integer SIZE is a number. For TYPE in doux, SIZE may also be C for sizeof(char), S for sizeof(short), I for sizeof(int) or L for sizeof(long). If TYPE is f, SIZE may also be F for sizeof(float), D for sizeof(double) or L for sizeof(long double). RADIX is d for decimal, o for octal, x for hexadecimal or n for none. BYTES is hexadecimal with 0x or 0X prefix, it is multiplied by 512 with b suffix, by 1024 with k and by 1048576 with m. Adding a z suffix to any type adds a display of printable characters to the end of each line of output. --string without a number implies 3. --width without a number implies 32. By default, od uses -A o -t d2 -w 16. AUTHOR
Written by Jim Meyering. REPORTING BUGS
Report bugs to <bug-coreutils@gnu.org>. COPYRIGHT
Copyright (C) 2002 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICU- LAR PURPOSE. SEE ALSO
The full documentation for od is maintained as a Texinfo manual. If the info and od programs are properly installed at your site, the com- mand info od should give you access to the complete manual. od (coreutils) 4.5.3 February 2003 OD(1)
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