Hi Mike,

several years ago we have discussed the interactive prompting using cl.ukey in loop here:
http://iraf.net/phpBB2/viewtopic.php?p=136735

I have written some script using it but today I have realized by a mistake in input that in fact it does not work correctly. After more detailed investigation it seems that there is something strange about the handling of the special characters in the solution you have suggested.

I have extracted the core of the logic in following test program

  1  procedure testukey.cl
  2 
  3 begin
  4 string ch
  5 for (ch = "c"; ch != "z"; ch = cl.ukey) {
  6             if (ch < "a") {
  7                 print (ch)
  8                 print ("got a newline")
  9             } else {
 10                 print (ch)
 11 switch (ch) {
 12             case "?":   print ("help for commands here...")
 13             case "h":   print ("imheader (imname, long+)")
 14             case "e":   print ("imexamine (imname, 1)")
 15             case "d":   print ("display (imname, 1, fill+)")
 16             case "n":   break   # next image
 17             case "q":   goto cleanup
 18             case "s":   print ("imstat (imname)")
 19             }
 20             printf ("Command? ")
 21         }
 22         }
 23         print('finishing loop')
 24         cleanup:
 25         printf("\nfinished \n-------------\n")
 26 end

For most letters it works correctly but it does not react to '?' as expected - as it is in ASCII table before 'a' so it is trapped as well as ENTER (\015) and more other codes (it is not desired effect anyway).

But when I change the trap condition for characters lower (in ASCII code position) then 'a' the system prints an error when entering
ENTER (\015) and SPACE (\040)

After some experiments it seems that the critical boundary is the '\' character - but it may not be put in the test at line 6 (complaining
immediately :

ERROR on line 6: Newline while processing string
    testukey ()

If giving the ']' character (next higher than backslash)
it works - it prints

\015
got a newline 

(for ENTER)

or

\040
got a  newline

for SPACE bar

If giving the first lower char that backslash - the '[' - it starts to complain

c
Command? \015
ERROR on line 26: Illegal switch value.
    testukey ()

So it is clean that the condition on line 6 does not trap the special characters and it somehow intrudes the second part after else

It does not help even the condition

if (ch =="\015")

Can you explain this strange behaviour ? Is there some solution for trapping fully the control characters (like ENTER SPACE) ?

Is there some function in IRAF that would allow to make the scancode number from the ukey input - so I could compare just integer numbers without the strange side effects ?
Thanks

Petr Skoda

The thing to remember is that the backslash is used as an escape, and so it needs to be escaped itself. Its a kludge, but try something like

begin
    char ch

    while (yes) {
        ch = cl.ukey

        if (substr(ch,1,4) == "\\015") {
            print ("do newline")
        } else if (substr(ch,1,4) == "\\040") {
            print ("do spacebar")
        } else {
            switch (ch) {
            case "q":   break
            case "a":   print ("got an 'a'")
            case "?":   print ("do help")
            case "\\":  print ("do backslash")
            }
        }
    }
end

-Mike

Thanks Mike!
It works nicely for me - I did not realize the representation of a scancode is really a normal string - I was thinking about a special treatment of control codes...

Petr Skoda