Vugen: Replace Any String With Another

Here is an easy way to replace anything with anything in a captured string in your LoadRunner Vugen script. It is a function called “string_replace”. Place this in the top of your action section, right after the include but before the main section begins:

char *string_replace(char *input_string,
    char *substring_to_be_replaced,
    char *substitution_string)
// strstr function declaration
 char *strstr(const char *s1, const char *s2); 
// newstring variable the new string to be returned
// increase the buffer size if needed. Default is 200
char newstring[200]=""; 
// str is a temporary pointer to aid in creation of newstring;
// it points at the beginning of each substring that
// needs to be included in the new string.
char *str; 
// ptr is a pointer to hold strstr result.
char *ptr; 
str = input_string;
// search for substring_to_be_replaced and
// replace with substitution_string
 while((ptr = strstr(input_string, substring_to_be_replaced))!=NULL)
 input_string = &ptr[strlen(substring_to_be_replaced)];
 ptr[0] = '\0';
 strcat(newstring, str);
 strcat(newstring, substitution_string);
 str = input_string;
// concatenate the rest of the string
strcat(newstring, input_string);
return newstring;

Now here is an example of how this might be used. Let’s say you captured a string that had “&amp” in it and you need to replace them with simply a “&” character. You need to search the string and replace multiple occurrences. This is what it might look like in your action section:

lr_output_message("newstring: %s", lr_eval_string("{pNewString}"));
return 0;

Here is what the output/execution log might look like in Vugen with standard logging turned on:

Running Vuser…
Starting iteration 1.
Starting action Action.
Action.c(34): newstring: Value=RS=&;OI=&;LI=&;BD=20020107&;ED=99991231&;SQ=0&;XXXXX;
Ending action Action.
Ending iteration 1.
Ending Vuser…
Starting action vuser_end.
Ending action vuser_end.
Vuser Terminated.

Notice that this function saves the string as pInputString. This may be changed to dynamically pull a value from a web page with the web_reg_save_param() function too. Also, notice how string_replace() is used to scan, replace, and save the new string by being embedded in the lr_save_string() function. The lr_output_message() is totally optional. Instead you might actually use the {pNewString} parameter in your script where it is needed.

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Scott Moore

About Scott Moore (153 articles)

With over 20 years of IT experience with various platforms and technologies, Scott has tested some of the largest applications and infrastructures in the world. He is a Certified Instructor and Certified Product Consultant in HP’s LoadRunner and Performance Center products. He currently holds HP certifications for ASE, ASC, and CI. A thought leader in the APM space, he speaks regularly at IT conferences and events

  • Visitor1

    I cant believe no one has commented yet. You just saved me hours of googling around to remember my C!

  • Michael

    Very helpful indeed. Thanks :)