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Top Forums UNIX for Dummies Questions & Answers making a .sh wait for user input Post 46665 by Perderabo on Wednesday 21st of January 2004 09:19:44 PM
Old 01-21-2004
Don't apologize. There is nothing wrong with posting a followup to an old thread. The only problem is it would take a book to really answer your question. I'll take a shot at a summary.

The tty driver controls how input lines that you type are delivered to programs. Normally a tty driver will wait until a complete line is available. It also handles stuff like backspace so that program doesn'y need to. The stty command lets you change the way the tty driver works. "stty -a" will display all of the settings. You should do that to see what's available.

"stty -g" displays all of the settings too. But it's encoded and you can't understand the output. But you can save the output and feed it back into the stty command. So:
oldtty=`stty -g`
stty $oldstty
will save and restore the original settings of the tty driver.

stty -canon -echo min 1 time 0
is setting some options in the tty driver. -icanon turns off all special character processing. Now a backspace will be passed to the program rather than being processed. And a carriage return won't terminate a line. So now min and time control when a read has finished. "min 1" says we need at least one character. "time 0" means that we won't wait a while before completing a read. So each read from the program may return after just one character.

the -echo just turns off echo. I would not have done that.

dd is a program that is prepared to read data that is not organized into lines. This dd will read one block (count=1) of data. And that block will be one character in length (size=1). So the dd will read one character and return to the script.

The final echo moves the cursor to the next line.
 

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IO::Stty(3)						User Contributed Perl Documentation					       IO::Stty(3)

NAME
Change and print terminal line settings SYNOPSIS
# calling the script directly stty.pl [setting...] stty.pl {-a,-g,-v,--version} # Calling Stty module use IO::Stty; IO::Stty::stty(*TTYHANDLE, @modes); use IO::Stty; $old_mode=IO::Stty::stty(*STDIN,'-g'); # Turn off echoing. IO::Stty::stty(*STDIN,'-echo'); # Do whatever.. grab input maybe? $read_password = <>; # Now restore the old mode. IO::Stty::stty(*STDIN,$old_mode); # What settings do we have anyway? print IO::Stty::stty(*STDIN,'-a'); DESCRIPTION
This is the PERL POSIX compliant stty. INTRO
This has not been tailored to the IO::File stuff but will work with it as indicated. Before you go futzing with term parameters it's a good idea to grab the current settings and restore them when you finish. stty accepts the following non-option arguments that change aspects of the terminal line operation. A `[-]' before a capability means that it can be turned off by preceding it with a `-'. stty parameters Control settings [-]parenb Generate parity bit in output and expect parity bit in input. [-]parodd Set odd parity (even with `-'). cs5 cs6 cs7 cs8 Set character size to 5, 6, 7, or 8 bits. [-]hupcl [-]hup Send a hangup signal when the last process closes the tty. [-]cstopb Use two stop bits per character (one with `-'). [-]cread Allow input to be received. [-]clocal Disable modem control signals. Input settings [-]ignbrk Ignore break characters. [-]brkint Breaks cause an interrupt signal. [-]ignpar Ignore characters with parity errors. [-]parmrk Mark parity errors (with a 255-0-character sequence). [-]inpck Enable input parity checking. [-]istrip Clear high (8th) bit of input characters. [-]inlcr Translate newline to carriage return. [-]igncr Ignore carriage return. [-]icrnl Translate carriage return to newline. [-]ixon Enable XON/XOFF flow control. [-]ixoff Enable sending of stop character when the system input buffer is almost full, and start character when it becomes almost empty again. Output settings [-]opost Postprocess output. Local settings [-]isig Enable interrupt, quit, and suspend special characters. [-]icanon Enable erase, kill, werase, and rprnt special characters. [-]echo Echo input characters. [-]echoe, [-]crterase Echo erase characters as backspace-space-backspace. [-]echok Echo a newline after a kill character. [-]echonl Echo newline even if not echoing other characters. [-]noflsh Disable flushing after interrupt and quit special characters. * Though this claims non-posixhood it is supported by the perl POSIX.pm. [-]tostop (np) Stop background jobs that try to write to the terminal. Combination settings ek Reset the erase and kill special characters to their default values. sane Same as: cread -ignbrk brkint -inlcr -igncr icrnl -ixoff opost isig icanon echo echoe echok -echonl -noflsh -tostop also sets all special characters to their default values. [-]cooked Same as: brkint ignpar istrip icrnl ixon opost isig icanon plus sets the eof and eol characters to their default values if they are the same as the min and time characters. With `-', same as raw. [-]raw Same as: -ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr -icrnl -ixon -ixoff -opost -isig -icanon min 1 time 0 With `-', same as cooked. [-]pass8 Same as: -parenb -istrip cs8 With `-', same as parenb istrip cs7. dec Same as: echoe echoctl echoke -ixany Also sets the interrupt special character to Ctrl-C, erase to Del, and kill to Ctrl-U. Special characters The special characters' default values vary from system to system. They are set with the syntax `name value', where the names are listed below and the value can be given either literally, in hat notation (`^c'), or as an integer which may start with `0x' to indicate hexadecimal, `0' to indicate octal, or any other digit to indicate decimal. Giving a value of `^-' or `undef' disables that special character. intr Send an interrupt signal. quit Send a quit signal. erase Erase the last character typed. kill Erase the current line. eof Send an end of file (terminate the input). eol End the line. start Restart the output after stopping it. stop Stop the output. susp Send a terminal stop signal. Special settings min N Set the minimum number of characters that will satisfy a read until the time value has expired, when <E>-icanon<E> is set. time N Set the number of tenths of a second before reads time out if the min number of characters have not been read, when -icanon is set. N Set the input and output speeds to N. N can be one of: 0 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200 38400 exta extb. exta is the same as 19200; extb is the same as 38400. 0 hangs up the line if -clocal is set. OPTIONS -a Print all current settings in human-readable form. -g Print all current settings in a form that can be used as an argument to another stty command to restore the current settings. -v,--version Print version info. Direct Subroutines stty() IO::Stty::stty(*STDIN, @params); From comments: I'm not feeling very inspired about this. Terminal parameters are obscure and boring. Basically what this will do is get the current setting, take the parameters, modify the setting and write it back. Zzzz. This is not especially efficent and probably not too fast. Assuming the POSIX spec has been implemented properly it should mostly work. show_me_the_crap() Needs documentation AUTHOR
Austin Schutz <auschutz@cpan.org> (Initial version and maintenance) Todd Rinaldo <toddr@cpan.org> (Maintenance) BUGS
This is use at your own risk software. Do anything you want with it except blame me for it blowing up your machine because it's full of bugs. See above for what functions are supported. It's mostly standard POSIX stuff. If any of the settings are wrong and you actually know what some of these extremely arcane settings (like what 'sane' should be in POSIX land) really should be, please open an RT ticket. ACKNOWLEDGEMENTS
None COPYRIGHT &; LICENSE Copyright 1997 Austin Schutz, all rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. perl v5.18.2 2017-10-06 IO::Stty(3)
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