System Calls using C w/BASH Post: 302611727

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Top Forums Programming System Calls using C w/BASH Post 302611727 by whyte_rhyno on Friday 23rd of March 2012 11:14:03 AM

03-23-2012

Registered User

Quote:

Originally Posted by Corona688

Your buffer only has five bytes of space.

Writing beyond that is rampaging through stack space, overwriting every local variable behind it until it finds and corrupts your stack frame itself, crashing your program the next time it tries to do anything to the stack.

Code:

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

int main(int argc, char *argv[])
{
    
    int i;
    char theCommand[16384] = "cat ";
  
    for (i = 1; i < argc; i++)
    {
        strcat(theCommand, argv[i]);
    }
    strcat(theCommand, " >> testfile.txt");
    system(theCommand);

    return 0;
}

D'oh! That would explain the segmentation fault, then.

Thank you very much for your help!

I had to put some white space in between the files because it was concatenating them together like: file.txtfile2.txtfile3.txt, is this the acceptable way of doing it (below)?

Code:

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

int main(int argc, char *argv[])
{
    
    int i;
    char theCommand[16384] = "cat ";
  
    for (i = 1; i < argc; i++)
    {
        strcat(theCommand, argv[i]);
        strcat(theCommand, " ");
    }
    strcat(theCommand, " >> testfile.txt");
    system(theCommand);

    return 0;
 }

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diff

DIFF(1) 						      General Commands Manual							   DIFF(1)

NAME

       diff - print differences between two files

SYNOPSIS

       diff   [-c | -e | -C n] [-br]file1 file2

OPTIONS

       -C n   Produce output that contains n lines of context

       -b     Ignore white space when comparing

       -c     Produce output that contains three lines of context

       -e     Produce an ed-script to convert file1 into file2

       -r     Apply diff recursively to files and directories of

EXAMPLES

       diff file1 file2    # Print differences between 2 files

       diff -C 0 file1 file2
			   # Same as above

       diff -C 3 file1 file2
			   # Output three lines of context with every

       diff -c file1 file2 # Same

       diff /etc /dev	   # Compares recursively the directories /etc and /dev

       diff passwd /etc    # Compares ./passwd to /etc/passwd

DESCRIPTION

       the same name, when file1 and file2 are both directories" difference encountered"

       Diff  compares  two files and generates a list of lines telling how the two files differ.  Lines may not be longer than 128 characters.	If
       the two	arguments on the command line are both directories, diff recursively steps through all subdirectories comparing files of the  same
       name.  If  a  file  name is found only in one directory, a diagnostic message is written to stdout. A file that is of either block special,
       character special or FIFO special type, cannot be compared to any other file.  On the other hand, if there is one directory  and  one  file
       given on the command line, diff tries to compare the file with the same name as file in the directory directory.

SEE ALSO

       cdiff(1), cmp(1), comm(1), patch(1).

																	   DIFF(1)

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