Types of perform in COBOL.....

IN-LINE perform :
                   in an in-line perform the paragraph name is omitted and it should be delimited by the END-PERFORM phrase.

syntax:

PROCEDURE DIVISION.
          PERFORM .......
                STATEMENT 1
                ....                  2
                ....                  3
          END-PERFORM.

 Here all the statements under the perform will get executed till the END-PERFORM phrase is reached.

The PERFORM statement formats are:
1.  Basic PERFORM
2.  TIMES phrase PERFORM
3.  UNTIL phrase PERFORM
4.  VARYING phrase PERFORM

Basic PERFORM.
                PERFORM para-1 thru para-2
               
                PERFORM
                      imperative statement
                END-PERFORM.

 PERFORM with UNTIL phrase
                PERFORM procedure-1 thru procedure-2 until condition-1.

If the condition is true the PERFORM statement is initiated, the specified procedures are not executed.

PERFORM with VARYING phrase
                PERFORM para-1 thru para-3 varying N from 1 by 1 until N > 5.

In the above example Para-1 thru Para-3 will be executed 5 times.