news@massey.ac.nz (USENET News System) (11/26/90)
I have an sh script that asks the user a question and reads the answer into a variable in the usual method. I want to be able to flush the input buffer just before the read so that any slips or double key bounces get ignored, rather than used as the answer. I realize this disables type ahead, but I can live with that. Anyone know how to do this? Thanx, -- Ken Spagnolo - Systems Programmer, Postmaster, Usenet Administrator, etc. Computer Centre, Massey University, Palmerston North, New Zealand K.Spagnolo@massey.ac.nz Phone: +64-63-69099 x8587 New Zealand = GMT+12
tif@doorstop.austin.ibm.com (Paul Chamberlain) (11/27/90)
In article <1990Nov26.001425.15563@massey.ac.nz> K.Spagnolo@massey.ac.nz (Ken Spagnolo) writes: >I want to >be able to flush the input buffer just before the read ... This is pretty nasty but it might do what you want: old_modes=`stty -g` # save old modes stty -icanon min '^@' time '^@' # read whats already there read junk # read all thats waiting stty $old_modes # restore old modes You may want to make this bullet-proof about interrupts though. I tried this on AIX Version 2 (RT). Paul Chamberlain | I do NOT represent IBM. tif@doorstop, sc30661 at ausvm6 512/838-7008 | ...!cs.utexas.edu!ibmchs!auschs!doorstop.austin.ibm.com!tif
martin@mwtech.UUCP (Martin Weitzel) (11/27/90)
In article <1990Nov26.001425.15563@massey.ac.nz> K.Spagnolo@massey.ac.nz (Ken Spagnolo) writes: >I have an sh script that asks the user a question and reads >the answer into a variable in the usual method. I want to >be able to flush the input buffer just before the read so >that any slips or double key bounces get ignored, rather than >used as the answer. I realize this disables type ahead, but >I can live with that. Anyone know how to do this? The exact answer depends on your variant of UNIX. Check the ioctl(2) and/or termio(7) entry of your manual. Usually it describes some method of how to clear the input buffer. Then write a small C-program (usually a two-liner) and call that program before executing the read-command of the shell. On the system I use (ISC UNIX 2.2) such a flush-program could look like: #include <termio.h> main() { (void) ioctl(0, TCFLSH, 0); return 0; } Alternatively, (and as you have to call a program anyway), you may choose to let your program read one line of input, and assign this input within the script by means of the `.....` construct. To save some more typing, you should include the desired prompt as an argument of your program. Instead of: echo "now> \c" # send prompt to the user flush # your program to flush input buffer read var # read user's input into var use var=`readline 'now> '` Here is a very simple version of a readline-program: #include <termio.h> #define MAXLINE 80 main(argc, argv) int argc; char *argv[]; { char buffer[MAXLINE]; int n; if (argc > 1) write(1, argv[1], strlen(argv[1])); (void) ioctl(0, TCFLSH, 0); n = read(0, buffer, MAXLINE); if (n <= 0) return 1; (void) write(1, buffer, n-1); return 0; } With more work, (considerably more work, if you want it portable) you could even add more or less simple editing functions to this program. (I've done so long time ago, using the termcap database to specify cursor-keys and control-codes, but the resulting program is too large to be posted here.) -- Martin Weitzel, email: martin@mwtech.UUCP, voice: 49-(0)6151-6 56 83
D. Allen [CGL]) (11/28/90)
In my limited experience stty old new will flush typeahead in a shell script that has a real tty from which it is reading. (BSD 4.3 Unix) -- -IAN! (Ian! D. Allen) idallen@watcgl.uwaterloo.ca idallen@watcgl.waterloo.edu [129.97.128.64] Computer Graphics Lab/University of Waterloo/Ontario/Canada
csx040@cck.cov.ac.uk (Alan Chantler (CS)) (11/30/90)
In article <1990Nov26.001425.15563@massey.ac.nz> K.Spagnolo@massey.ac.nz (Ken Spagnolo) writes: >I have an sh script that asks the user a question and reads >the answer into a variable in the usual method. I want to >be able to flush the input buffer just before the read so >that any slips or double key bounces get ignored, rather than >used as the answer. I realize this disables type ahead, but >I can live with that. Anyone know how to do this? OK This is not quite the answer that you seek, but it may help. Whenever I want a script to read into a variable (say 'fubar') then I use: read fubar junk This will capture any 'extras' into 'junk', which I ignore. Of course it doesn't work unless there is whitespace after legitimate input, but it can be extended for any number of inputs on a line: read x y z junk etc. -- AlanC@coventry.ac.uk | Post: Coventry Polytechnic JANET: AlanC@uk.ac.coventry | Priory Street INET : AlanC%coventry.ac.uk@nsfnet-relay.ac.uk | Coventry, UK Phone: +44 203 838332 | CV1 5FB