Before we give the exercise assignments, we suggest you review
Appendix C: REXX Goodies. These tools
may help you when you code your procedures.
Play REXX interpreter
The first exercise is a paper exercise, whereby
it is your turn to comment on our procedure. Next piece of coding
contains some errors and bad coding techniques. Don't
search only for bugs, but also for lines that could be coded better.
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/* */ /* DESSERT EXEC */
/* 1*/ Parse source . . myname mytype . syn .
/* 2*/ Parse arg args
/* 3*/ Parse value translate(diag(8,'Q SET'),' ',','!!'15'X) ,
/* 4*/ with a b c d e emsg .
/* 5*/ parse value 0 0 1 (emsg^='OFF' ) '*' ,
/* 6*/ with zero nok ok emsg fmode .
/* 7*/ Say 'Hi there, you called' myname mytype 'by typing:'
/* 8*/ Say ' 'syn args
/* 9*/ if emsg then Say 'You will see eventual errormessages.'
/*10*/ else Say 'Aha you want to hide the errors you make.'
/*11*/
/*12*/ do until ok
/*13*/ Say 'Do you want to see something or just be lazy ?'
/*14*/ Say ' anwser Y or N or FILELIST * * fmode'
/*15*/ Parse upper pull answer
/*16*/ ok=1 /* Suppose Answer is OK */
/*17*/ if answer='' then answer='Y' /* get the lazy at work */
/*18*/ parse var anwser with w1 w2 w3 w4 .
/*19*/ select
/*20*/ when abbrev(NO,w1) then exit
/*21*/ when abbrev('YES',w1,1) then 'FILELIST * *' fmode
/*22*/ when abbrev(FILELIST,w1,1) then 'FILELIST' w2 w3 w4
/*23*/ Otherwise
/*24*/ Say 'Can''t you read ?, please give a valid answer.'
/*25*/ ok=0
/*26*/ End
/*27*/ End
/*28*/ Exit
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This is a complementary question:
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24 |
What is the best form of PARSE to ask the user for a reply to a
question ?
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Practice parsing by counting filetypes
Now, we propose you to write a procedure where parse will
be useful.
The exercise is not so easy, though it is possible to do it in less
than 20 statements...
Write a procedure that lists the different filetypes found on an
accessed disk or SFS directory, and also displays the frequency at
which they are found. The output we expect is thus something like
this:
There are 7 files with filetype EXEC on your B-disk
There are 13 files with filetype XEDIT on your B-disk
...
The procedure should accept a filemode as parameter (so don't
hard-code a filemode !).
We also
explicitly ask you not to use CMS Pipelines but to search
for the best solution using REXX logic (this is a very good exercise
to practice the possibilities of REXX).
Test your procedure with a disk containing only a few files
so that you can easily verify your results via
a FILELIST.
But then, stress test it on a larger disk (e.g. the Y-disk).
You can then review our commented solution.
Practice parsing by analyzing a file
And finally, an exercise on File I/O.
Write a procedure that lists the logical shared segments (LSEGMENT)
that are part of the physical shared segment (PSEGMENT) (for example
CMSFILES). The procedure should also display the size in bytes
for each logical segment, and calculate the
remaining free space in the physical segment.
The information can be found in file SYSTEM SEGID S2.
The records that you have to extract look like these:
PSEGMENT CMSFILES 01C00000 00190000 02/17/94 13:42:33
LSEGMENT xxxxxx 01C00000 000C64E8
LSEGMENT yyyyyy 01CC6528 000C31B0
The fourth column indicates the sizes in hexadecimal notation. So the
remaining free space is the size of the PSEGMENT minus the sum of the
LSEGMENT members.
Your output should resemble to this:
Physical segment CMSFILES contains following logical segments :
DMSDAC size 812264 bytes
DMSSAC size 799152 bytes
Space remaining in physical segment = 26984 bytes
Choose any of the methods described in the lesson. EXECIO,
XEDIT or CMS Pipelines are the most appropriate as they
have options or functions to find the correct records. LINEIN
doesn't have the options, so that you have to put a bit more logic in
the procedure. Allow for the name of the physical segment to be passed as
parameter.
You can then review our commented solution.
Lesson 4 (chapter 14) will now go into a lot more details about file I/O.