If you want to use snoop or tcpdump with advanced search in the packet, then you would need to convert the string to hex string. For this, either you can use a web search and find some web application to do that or you can use a simple C program like this 🙂
/*
* =====================================================================================
*
* Filename: ascii.c
*
* Description: ascii to dec
*
* Version: 1.0
* Ceated: 03/02/2012 12:08:49 PM
* Revision: none
* Compiler: gcc
*
* Author: Amit Agarwal (aka), amit.agarwal@roamware.com
* Last modified: Thu Mar 08, 2012 08:47PM
*
* =====================================================================================
*/
void main (int argc, char **argv){
int i=0;
char a[200]="",b[200]="";
printf("String - %s, Length - %d\n",argv[1],strlen(argv[1]));
/*printf("%x\n 0x",argv[1]);*/
while (i < strlen(argv[1])){
/*printf("%c",argv[1][i]);*/
sprintf(a,"%s%x",a,argv[1][i]);
/*printf("a=%s\n",a);
printf("b=%s\n",b);*/
sprintf(b,"%s%d",b,argv[1][i]);
i++;
}
printf ("\n");
printf ("String : %s\n",argv[1]);
printf ("Hex : 0x%s\n", a);
printf ("Dec : %s\n", b);
}