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Full Discussion: Retrieving command line arguments of a particular PID
Top Forums UNIX for Advanced & Expert Users Retrieving command line arguments of a particular PID Post 302252171 by Andrewkl on Tuesday 28th of October 2008 10:05:38 PM
Old 10-28-2008
hi,

Thank you for the tip.

I am able to read in the contents of the "cmdline" file into a variable,
but when I try to print out the string, the output shows only characters before
the first null character.

How do I get the other characters after the first null character.
You suggested that i use pointer arithmetic, but how do i'm not sure
how to get the index of the '\0'.

I used strtok(), but it stops processing after the first null.

my code is below.
-------------------------------------------------

% cd /proc/14007
% cat cmdline
emacs--background-colorblack/tmp/abc

---------------------------

% ps -e -o pid,args | grep 14007
14007 emacs --background-color black /tmp/abc

---------------------------------------

% a.out /proc/14007/cmdline
file length is: 0
content is [emacs] <<<<<----- everything after first null character is not shown
strlen: 5
1: emacs
Tokenizing complete


==============================================================
Code:
#include <stdio.h>


main (int argc, char *argv[])
{
  FILE *fp;
  char *tok;
  int x = 1;
                  
  long  lFileLen;               /* Length of file */
  char *contents;                  /* Dynamically allocated buffer (entire file) */

  if (argc < 2) {
     printf("need a filename\n");
     exit(1);
  }

  fp = fopen(argv[1], "r"); /* Open in BINARY mode */
  if (fp == NULL) {
      printf("could not open file\n");
      exit(2);
  }

  fseek(fp, 0L, SEEK_END);  /* Position to end of file */
  lFileLen = ftell(fp);     /* Get file length */
  rewind(fp);               /* Back to start of file */

  printf("file length is: %ld\n", lFileLen);
 
  lFileLen = 200; /* assume there are 200 bytes at most */
  
  contents = (char*)calloc(lFileLen + 1, sizeof(char));

  if(contents == NULL )
  {
    printf("\nInsufficient memory to read file.\n");
    return 0;
  }

  /* Read the entire file into contents */
  fread(contents, lFileLen, 1, fp); 
  
  fclose(fp);

  printf("content is [%s]\n", contents);  /* nothing after first null character !!! */
  printf("strlen: %d\n", strlen(contents)); 
  
   /* extract first string from string sequence */
  tok = (char*)strtok(contents, "\0");

  /* print first string after tokenized */
  printf("%i: %s\n", x, tok);

  /* loop until finishied */
  while (1) 
  { 
          /* extract string from string sequence */
          tok = (char*)strtok(NULL, "\0");

          /* check if there is nothing else to extract */
          if (tok == NULL)
          {
                  printf("Tokenizing complete\n");
               /*   exit(0); */
                  break;
          } 

          /* print string after tokenized */
          printf("/%i: %s\n", x, tok);
          x++;
  } 


  free(contents);

}

Last edited by Andrewkl; 10-29-2008 at 01:40 AM..
 

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LEARN ABOUT OPENSOLARIS

chroot

chroot(1M)						  System Administration Commands						chroot(1M)

NAME

       chroot - change root directory for a command

SYNOPSIS

       /usr/sbin/chroot newroot command

DESCRIPTION

       The  chroot  utility causes command to be executed relative to newroot. The meaning of any initial slashes (/) in the path names is changed
       to newroot for command and any of its child processes. Upon execution, the initial working directory is newroot.

       Notice that redirecting the output of command to a file,

	 chroot newroot command >x

       will create the file x relative to the original root of command, not the new one.

       The new root path name is always relative to the current root. Even if a chroot is currently in effect, the newroot argument is relative to
       the current root of the running process.

       This command can be run only by the super-user.

RETURN VALUES

       The exit status of chroot is the return value of command.

EXAMPLES

       Example 1 Using the chroot Utility

       The  chroot  utility  provides an easy way to extract tar files (see tar(1)) written with absolute filenames to a different location. It is
       necessary to copy the shared libraries used by tar (see ldd(1)) to the newroot filesystem.

	 example# mkdir /tmp/lib; cd /lib
	 example# cp ld.so.1 libc.so.1 libcmd.so.1 libdl.so.1 
		  libsec.so.1 /tmp/lib
	 example# cp /usr/bin/tar /tmp
	 example# dd if=/dev/rmt/0 | chroot /tmp tar xvf -

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       cd(1), tar(1), chroot(2), ttyname(3C), attributes(5)

NOTES

       Exercise extreme caution when referencing device files in the new root file system.

       References by routines such as ttyname(3C) to stdin, stdout, and stderr will find that the device associated with the  file  descriptor	is
       unknown after chroot is run.

SunOS 5.11							    15 Dec 2003 							chroot(1M)
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