JCL program to compare two files

//SORTTOOL EXEC PGM=SORT 
//TOOLMSG DD SYSOUT=* 
//DFSMSG DD SYSOUT=* 
//SYSOUT DD SYSOUT=* 
//SORTJNF1 DD DSN=FIRST.FILENAME,DISP=SHR 
//SORTJNF2 DD      DSN=SECOND.FILENAME,DISP=SHR 
//SORTOUT DD DSN=THIRD.FILENAME,DISP=SHR 
//SYSIN DD * 
 SORT FIELDS=COPY 
 JOINKEYS FILES=F1,FIELDS=(1,10,A) 
 JOINKEYS FILES=F2,FIELDS=(1,10,A) 
 REFORMAT FIELDS=(F1:1,80) 
/* 

The key I compared starts at 1 and has length of 10 bytes.