String output for system()

[voron00]

this is for voron

Right yeah thx, actially its possible to do it w/o reallocating the memory and still getting the last line of the result: https://github.com/voron00/libcod/co...9b91bba6b580d0

[kung foo man]

Just this:

		
void gsc_utils_execute() { // Returns complete command output as a string
    char *cmd;
    if ( ! stackGetParams("s",  &cmd)) {
        printf("scriptengine> ERROR: please specify the command as string to gsc_execute_command()\n");
        stackPushUndefined();
        return;
    }
    setenv("LD_PRELOAD", "", 1); // dont inherit lib of parent
    char *result = exec(cmd);
    stackPushString( result );
    free(result); // <------
} 
	

Because:

http://man7.org/linux/man-pages/man3/getline.3.html

getline() reads an entire line from stream, storing the address of
the buffer containing the text into *lineptr.  The buffer is null-
terminated and includes the newline character, if one was found.

If *lineptr is set to NULL and *n is set 0 before the call, then
getline() will allocate a buffer for storing the line.  This buffer
should be freed by the user program even if getline() failed.

And init the char *result in exec(char *) to NULL, since setting a pointer to NULL automatically is "luck" (depending on compiler if they init it).

Full test:

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

char *exec(const char* command) {
    FILE *fp;
    char *result = NULL; // plz init, otherwise it COULD be non-NULL (depending on compiler)
    size_t len = 0;
    fp = popen(command, "r");
    if (fp == NULL) {
        printf("Cannot execute command:\n%s\n", command);
        return NULL;
    }
    while(getline(&result, &len, fp) != -1) {
        fputs(result, stdout); // nice for debugging, but in actual release server kinda spammy to print every result
    }
    pclose(fp);
    return result;
}

int main() {
    char *result = exec("ls -l");
    printf("ret: \"%s\"", result);
    free(result);
    return 0;
} 
	

Just compile it:

gcc exec.c -o exec.exe

And run it with valgrind: valgrind --tool=memcheck ./exec.exe

Everything will be ok then, but when you forget free(result);, valgrind will print the error:

k_tracker@euve78301:~$ valgrind --tool=memcheck ./exec.exe
==17356== Memcheck, a memory error detector
==17356== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==17356== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info
==17356== Command: ./exec.exe
==17356==
total 625772
-rwxr-xr-x  1 k_tracker k_tracker      1300 Dez 12  2014 autobahn2.js
-rwxr-xr-x  1 k_tracker k_tracker       913 Dez 10  2014 autobahn.js
drwxr-xr-x  3 k_tracker k_tracker      4096 Okt 15  2013 bin
drwxrwxr-x  2 k_tracker k_tracker      4096 Nov 30 05:21 boost
-rwxr-xr-x  1 k_tracker k_tracker     22803 Jan 21  2015 calculator.js
-rwxr-xr-x  1 k_tracker k_tracker      3737 Dez 10  2014 chat.js
drwxr-xr-x  2 k_tracker k_tracker      4096 Okt 15  2013 classes
-rwxr-xr-x  1 k_tracker k_tracker      3475 Nov 19  2012 debug.php
-rwxr-xr-x  1 k_tracker k_tracker       330 Dez 15  2014 dns.js
-rw-rw-r--  1 k_tracker k_tracker       516 Jan  3 03:15 exec.c
-rwxrwxr-x  1 k_tracker k_tracker      8832 Jan  3 03:15 exec.exe
drwxrwxr-x  2 k_tracker k_tracker      4096 Okt  1 03:06 filefront
-rw-rw-r--  1 k_tracker k_tracker       452 Okt  1 03:00 kt.txt
drwxr-xr-x  4 k_tracker k_tracker      4096 Okt 15  2013 lib
-rwxr-xr-x  1 k_tracker k_tracker      3380 Nov 19  2012 main.php
drwxr-xr-x 14 k_tracker k_tracker      4096 Dez  1 20:16 mariadb
-rwxr-xr-x  1 k_tracker k_tracker 309533236 Jun 17  2015 mariadb.1
-rw-rw-r--  1 k_tracker k_tracker 331091501 Okt 15 23:14 mariadb.tar.gz
-rwxr-xr-x  1 k_tracker k_tracker      3858 Jul  1  2015 my.cnf
drwxr-xr-x  7 k_tracker k_tracker      4096 Dez 10  2014 nodejs
drwxr-xr-x 28 k_tracker k_tracker      4096 Sep 24 16:07 node_modules
drwxr-xr-x  2 k_tracker k_tracker      4096 Jul  2  2015 ntop
-rwxr-xr-x  1 k_tracker k_tracker      6681 Nov 19  2012 query_master.js
-rwxr-xr-x  1 k_tracker k_tracker       335 Dez 10  2014 rpc.js
-rwxr-xr-x  1 k_tracker k_tracker        46 Okt 15  2013 server.sh
drwxr-xr-x  2 k_tracker k_tracker      4096 Sep 24 16:07 tmp
drwxr-xr-x  4 k_tracker k_tracker      4096 Jun 30  2015 tracker
drwxr-xr-x  4 k_tracker k_tracker      4096 Jun 30  2015 tracker_floater
drwxr-xr-x  5 k_tracker k_tracker      4096 Nov 15 00:13 tracker_iznogod
-rwxr-xr-x  1 k_tracker k_tracker       327 Jul 10  2014 unity2.js
-rwxr-xr-x  1 k_tracker k_tracker      1082 Jul 10  2014 unity.js
-rwxr-xr-x  1 k_tracker k_tracker       709 Dez 11  2014 wamp_client.js
-rwxr-xr-x  1 k_tracker k_tracker       238 Dez 11  2014 wamp.js
ret: "-rwxr-xr-x  1 k_tracker k_tracker       238 Dez 11  2014 wamp.js
"==17356==
==17356== HEAP SUMMARY:
==17356==     in use at exit: 120 bytes in 1 blocks
==17356==   total heap usage: 2 allocs, 1 frees, 376 bytes allocated
==17356==
==17356== LEAK SUMMARY:
==17356==    definitely lost: 120 bytes in 1 blocks
==17356==    indirectly lost: 0 bytes in 0 blocks
==17356==      possibly lost: 0 bytes in 0 blocks
==17356==    still reachable: 0 bytes in 0 blocks
==17356==         suppressed: 0 bytes in 0 blocks
==17356== Rerun with --leak-check=full to see details of leaked memory
==17356==
==17356== For counts of detected and suppressed errors, rerun with: -v
==17356== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
k_tracker@euve78301:~$

About the pointer syntax, the asterix belongs to the variable name. You can simply understand this, when you want e.g. 2 pointers. What do you write?

This?

char* a, b;

Or this?

char *a, *b;

Well, as said already, the 2nd way is the correct way, since the asterix belongs to the variable name.

Also why just return the last line? Just return an array with every line :^)

Simple example from scandir():

		void gsc_utils_scandir() {
    char *dirname;
    if ( ! stackGetParams("s", &dirname)) {
        stackPushUndefined();
        return;
    }
    DIR *dir;
    struct dirent *dir_ent;
    dir = opendir(dirname);
    if ( ! dir) {
        stackPushUndefined();
        return;
    }
    stackPushArray();
    while (dir_ent = readdir(dir)) {
        stackPushString(dir_ent->d_name);
        stackPushArrayLast();
    }
    closedir(dir);
} 
	

[maxdamage99]

Pth... What use me?