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Top Forums Shell Programming and Scripting Strange behavior from 'read' statements. (ksh - but could be same on other shells) Post 302070321 by alexop on Tuesday 4th of April 2006 04:52:17 AM
Old 04-04-2006
Strange behavior from 'read' statements. (ksh - but could be same on other shells)

I'm getting rather frustrated with an interactive script I'm writing.

The script is divided up, with section for setting variable at the top, then functions (which make up most of the script) then basically a line at the end which calls the first function- the program moves between the functions to do it's thing.

The problem I'm having is when I'm using 'read' to ask the user to 'press return to continue' or suchlike, at some points in the script this works FINE, however at other points it just continues straight through the 'read' without waiting for input or anything. Using 'read -u' had no effect, I have also replaced all these prompts with the following function;

pressreturn() {
echo
echo "Press <RETURN> to continue."
read BLANK
}

This has had no positive effect, the script still ignores the read statement some of the time!

I'm using ksh version M-11/16/88f on AIX 5.2

Thanks for your time on this, folks. I know I havn't provided too much information, I was just hoping this was a not-uncommon gotcha that a few of you might have come up against at one point or another. If anyone requires further information please shout and I'll supply whatever you need.

Regards,

Alex
 

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SCRIPT(1)						    BSD General Commands Manual 						 SCRIPT(1)

NAME
script -- make typescript of terminal session SYNOPSIS
script [-adkpqr] [-F pipe] [-t time] [file [command ...]] DESCRIPTION
The script utility makes a typescript of everything printed on your terminal. It is useful for students who need a hardcopy record of an interactive session as proof of an assignment, as the typescript file can be printed out later with lpr(1). If the argument file is given, script saves all dialogue in file. If no file name is given, the typescript is saved in the file typescript. If the argument command is given, script will run the specified command with an optional argument vector instead of an interactive shell. The following options are available: -a Append the output to file or typescript, retaining the prior contents. -d When playing back a session with the -p flag, do not sleep between records when playing back a timestamped session. -F pipe Immediately flush output after each write. This will allow a user to create a named pipe using mkfifo(1) and another user may watch the live session using a utility like cat(1). -k Log keys sent to the program as well as output. -p Play back a session recorded with the -r flag in real time. -q Run in quiet mode, omit the start, stop and command status messages. -r Record a session with input, output, and timestamping. -t time Specify the interval at which the script output file will be flushed to disk, in seconds. A value of 0 causes script to flush after every character I/O event. The default interval is 30 seconds. The script ends when the forked shell (or command) exits (a control-D to exit the Bourne shell (sh(1)), and exit, logout or control-D (if ignoreeof is not set) for the C-shell, csh(1)). Certain interactive commands, such as vi(1), create garbage in the typescript file. The script utility works best with commands that do not manipulate the screen. The results are meant to emulate a hardcopy terminal, not an addressable one. ENVIRONMENT
The following environment variables are utilized by script: SCRIPT The SCRIPT environment variable is added to the sub-shell. If SCRIPT already existed in the users environment, its value is overwrit- ten within the sub-shell. The value of SCRIPT is the name of the typescript file. SHELL If the variable SHELL exists, the shell forked by script will be that shell. If SHELL is not set, the Bourne shell is assumed. (Most shells set this variable automatically). SEE ALSO
csh(1) HISTORY
The script command appeared in 3.0BSD. The -d, -p and -r options first appeared in NetBSD 2.0 and were ported to FreeBSD 9.2. BUGS
The script utility places everything in the log file, including linefeeds and backspaces. This is not what the naive user expects. It is not possible to specify a command without also naming the script file because of argument parsing compatibility issues. When running in -k mode, echo cancelling is far from ideal. The slave terminal mode is checked for ECHO mode to check when to avoid manual echo logging. This does not work when the terminal is in a raw mode where the program being run is doing manual echo. If script reads zero bytes from the terminal, it switches to a mode when it only attempts to read once a second until there is data to read. This prevents script from spinning on zero-byte reads, but might cause a 1-second delay in processing of user input. BSD
December 4, 2013 BSD
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