Generally a single ampersand is used for a variable.
001150 // SET PARM1=’some.dataset’
//JCLIN DD DSN=&PARM1.,DISP=SHR
Two ampersands can be used for a temporary dataset.
002500 //SYSUT1 DD DSN=&&WORK,SPACE=(CYL,(5,5)),UNIT=DASD
You state “in my jcl after replacement of my variables, it is coming like ‘&&’. ”
What does your JCL look like? Can you show me the line or two involved ? What it looks like before submitting the job and what it looks like after submitting the job?
You aren’t by chance trying to replace a parm with a value that contains an ampersand, are you?