Ever wish there was a procedure that allowed you to use wildcards to detect the existence of a character pattern in a character string? The LIKE procedure now gives you this ability. It’s pattern matching made simple for RPG IV programs!

If you have ever needed to scan text to find a matching pattern, you will find this procedure helpful. The procedure is called LIKE because it is an RPG IV implementation of the Query/400 function and SQL predicate LIKE (an SQL predicate is much like a command or function). Pattern matching is more than simply scanning for matching characters. Pattern matching provides for the use of wildcards to indicate which positions will match any character and which positions to ignore. The LIKE procedure does these things.

The copybook containing the prototype is called LIKEPRO and is shown in Figure
1. The prototype shows that this procedure has seven parameters and returns a 1-byte numeric result. The result is 1 if the pattern is not found, and 0 if it is. The first parameter is the text to which the pattern is to be applied. The second parameter is the string containing the pattern to use. The third parameter (an optional parameter that I’ll explain in a moment) is the escape character. The other four parameters are used by the procedure if it determines it must call itself; they are not to be used by the user.

Two special characters are used: underscore (_) and percent sign (%). The _ is a wildcard; any character in this position in the text will be considered a match. The % means that any number of characters starting in this position in the text will match. The top of Figure 1 shows a simple example on the use of these special characters.

If you are looking for text that contains these special characters, you can use the escape parameter to tell the procedure to treat the character following it as data and not as a special character. You can use any character as an escape character. For example, suppose you are looking for the following string of characters: 'close_file'. This string has an underscore as part of the data. If you send this string to the LIKE procedure, LIKE will

interpret the underscore as a wildcard and will match any string that contains any character in that position. To tell LIKE the underscore is data (not a wildcard), use the escape parameter. If you specify a slash (/) as the escape character, you would rewrite the pattern this way: 'close/_file'. This way, LIKE sees the escape character and treats the character following it—in this case, the underscore—as data, not a wildcard.

The program used to test this procedure is called LIKETEST (see Figure 2). Its display file (see Figure 3) displays a screen with two input fields. In one, the user enters the text to search; in the other, the user enters the pattern. The program then places these two fields in variable-length variables and calls LIKE.

The procedure LIKE is available from the Midrange Computing Web site at http://www.midrangecomputing.com/mc/98/10. Since LIKE can call itself, it uses %PARM to determine if more than four parameters were passed. Because the user is supposed to pass no more than three parameters, more than three parameters indicates that LIKE is calling itself.

The only interesting point in this code is shown in Figure 4, where the % special character is processed. If there are more characters in the pattern after this special character and the next character is not another %, the program falls into a DOW loop. Remember: The % means that from 0 to any number of characters match. If there are more characters in the pattern to match, the LIKE procedure recursively processes the text and pattern until LIKE returns with a 0 return code, which means the program has successfully skipped the unknown number of characters it was supposed to ignore. This use of recursion makes the logic of this procedure simple.

Both LIKETEST and LIKE use the copybook that defines the prototype. In both cases, I have coded specific libraries and source files. You must change these /COPY statements to reflect the naming conventions used in your shop.

You now have a procedure you can use in other programs that need the LIKE functionality. This is not the type of program you would want to write over and over.

For instance, an inventory control program could display item number, item description, and item quantity in a subfile on the screen. A user who wants to find the item number for a particular item but doesn’t know the full description could put what he does know of the description, along with appropriate wildcards, in an input field on the screen. The program could then pass this pattern to the LIKE procedure for every description on the file and find just what the user wants to see.

* Purpose: LIKE will scan text looking for a user supplied pattern.

* It is functionally the same as the LIKE predicate.

* PATTERN- Text pattern to search for.

* % - matches on 0 to all characters.

* _ - matches on 1 character.

* ESC - Optional escape character.

* Use this immediately before either the '_'

* or '%' and that instance of that character

* will be treated as data and not as

* a special character.

*

* Example: text1 = 'ABACAAAD'

* pattern = 'AB_C%D'

* LIKE(text1:pattern') (This will match)

*

* SubProcedure ProtoType

D like PR 1P 0

D txtin 32767A VARYING

D pattern 32767A VARYING

D esc 1A OPTIONS(*NOPASS)

D textlen 10I 0 OPTIONS(*NOPASS)

D patlen 10I 0 OPTIONS(*NOPASS)

D txtindx 4P 0 OPTIONS(*NOPASS)

D patindx 4P 0 OPTIONS(*NOPASS)

Figure 1: Prototype for LIKE (LIKEPRO)

*****************************************************************

*

* To compile:

*

* CRTRPGMOD MODULE(xxx/LIKETEST) SRCFILE(xxx/QRPGLESRC) +

* TEXT('Program to test LIKE procedure')

*

* CRTPGM PGM(xxx/LIKETEST) MODULE(xxx/LIKETEST) +

* BNDSRVPGM(xxx/LIKE)

*****************************************************************

Fliketestd CF E WORKSTN

/COPY MAGWORK/SOURCE,LIKEPRO

D teststring S 32767A VARYING

D patstore S 32767A VARYING

C DOW *IN03 = *OFF

C EXFMT screen1

C CLEAR message

C SELECT

C WHEN *IN03 = *ON

C OTHER

C EVAL teststring = %TRIMR(textin)

C EVAL patstore = %TRIMR(pattern)

C IF LIKE(teststring:patstore) = 1

C EVAL message = 'Pattern does not match'

C ELSE

C EVAL message = 'Success!!'

C ENDIF

C ENDSL

C ENDDO

C EVAL *INLR = *ON

*****************************************************************

*

* To compile:

*

* CRTDSPF FILE(xxx/LIKETESTD) +

* SRCFILE(xxx/QDDSSRC) +

* TEXT('Display file for testing LIKE function')

*

*****************************************************************

A DSPSIZ(24 80 *DS3)

A PRINT

A R SCREEN1

A CA03(03 'Exit')

A 1 32'Test LIKE Procedure'

A DSPATR(HI)

A 8 7'Text:'

A TEXTIN 50A B 8 17CHECK(LC)

A 10 7'Pattern:'

A PATTERN 50A B 10 17CHECK(LC)

A 23 2'F3=Exit'

A COLOR(BLU)

A MESSAGE 70A O 24 2COLOR(RED)

C DOW pindx < plen + 1 AND

C tindx < txtlen + 1 AND

C error = 1

Figure 2: Test program (LIKETEST)

Figure 3: Display file used by test program (LIKETESTD)

Figure 4: Portion of LIKE procedure

Also Read

H and F Position-less Specs

Practical RPG: AI and IBM i

Programming in ILE RPG - Defining Standalone Variables & Assigning Initial Values to Data