bin/129566: behavioral change of "read" builtin for sh on 8-CURRENT

[Michael Proto]

>Number:         129566
>Category:       bin
>Synopsis:       behavioral change of "read" builtin for sh on 8-CURRENT
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu Dec 11 04:40:01 UTC 2008
>Closed-Date:
>Last-Modified:
>Originator:     Charlie &
>Release:        FreeBSD 8.0-CURRENT i386
>Organization:
>Environment:
System: FreeBSD minibsd8-dev.localnet 8.0-CURRENT FreeBSD 8.0-CURRENT #0: Thu Dec 4 15:58:57 EST 2008 root at minibsd8-dev.localnet:/usr/obj/usr/src/sys/MINIBSD8-DEV i386



>Description:
	I've noticed a behavioral difference of the "read" builtin statement within /bin/sh on CURRENT and I'm hoping someone can point me in the right direction on how to restore the old behavior.

I have a /bin/sh script that accepts input for IP address information:

#!/bin/sh
set -x
DEFINT=vr0
DEFIP=192.168.0.1
DEFMASK=255.255.255.0
read -p "Enter network interface [$DEFINT]: " -t 5 INT
read -p "Enter IP address [$DEFIP]: " -t 5 IP
read -p "Enter netmask [$DEFMASK]: " -t 5 MASK
echo ${INT:=$DEFINT} : ${IP:=$DEFIP}/${MASK:=$DEFMASK}


This script waits for terminal input for each of the above variables (INT, IP, MASK) and defaults to a script-provided value if no input is entered in 5 seconds for each variable. On 6.x and 7.x if I simply hit Enter at the prompt (and don't provide any input) no value is assigned to the variable so my INT, IP, and MASK variables are set to null and the parameter substitution of the DEF* variables works as expected.

On 8-CURRENT if I hit Enter with no input at the prompt the system seems to recognize the newline as input and continues to sit there until I hit Enter again. When I do this there appears to be a strange unprintable value assigned to the INT, IP, and MASK variables yet the variable subsitution doesn't work correctly.

The man page on sh lists the following behavior for read:

     read [-p prompt] [-t timeout] [-er] variable ...
             The prompt is printed if the -p option is specified and the stan-
             dard input is a terminal.  Then a line is read from the standard
             input.  The trailing newline is deleted from the line and the
             line is split as described in the section on White Space
             Splitting (Field Splitting) above, and the pieces are assigned to
             the variables in order.  If there are more pieces than variables,
             the remaining pieces (along with the characters in IFS that sepa-
             rated them) are assigned to the last variable.  If there are more
             variables than pieces, the remaining variables are assigned the
             null string.


As I interpret this, read should delete the trailing newline and assign a null value since there is is no "input" before the newline. Then the variable substitution should take over and assign the DEF* variables appropriately. 6 and 7 follow this but 8 does not.

Here's the output of the script (with set -x) to help show what I'm seeing.

This is on 6 and 7:

+ DEFINT=vr0
+ DEFIP=192.168.0.1
+ DEFMASK=255.255.255.0
+ read -p Enter network interface [vr0]:  -t 5 INT
Enter network interface [vr0]:
+ read -p Enter IP address [192.168.0.1]:  -t 5 IP
Enter IP address [192.168.0.1]:
+ read -p Enter netmask [255.255.255.0]:  -t 5 MASK
Enter netmask [255.255.255.0]:
+ echo vr0 : 192.168.0.1/255.255.255.0
vr0 : 192.168.0.1/255.255.255.0


And this is what I see with 8:

+ DEFINT=vr0
+ DEFIP=192.168.0.1
+ DEFMASK=255.255.255.0
+ read -p Enter network interface [vr0]:  -t 5 INT
Enter network interface [vr0]:
+ read -p Enter IP address [192.168.0.1]:  -t 5 IP
Enter IP address [192.168.0.1]:
+ read -p Enter netmask [255.255.255.0]:  -t 5 MASK
Enter netmask [255.255.255.0]:
/: cho
/:

Strange that the "echo" statement is missing the first "e" character in the debug output.

Even stranger on 8-CURRENT, if I *do* enter input before the newline (say I change the IP address or the network interface), the first character is not echoed back to the screen but is still saved to the variable. Here's an example when I run the script and provide input at each prompt:

+ DEFINT=vr0
+ DEFIP=192.168.0.1
+ DEFMASK=255.255.255.0
+ read -p Enter network interface [vr0]:  -t 5 INT
Enter network interface [vr0]: r0
+ read -p Enter IP address [192.168.0.1]:  -t 5 IP
Enter IP address [192.168.0.1]: 92.168.0.1
+ read -p Enter netmask [255.255.255.0]:  -t 5 MASK
Enter netmask [255.255.255.0]: 55.255.255.0
+ echo br0 : 192.168.0.1/255.255.255.0
br0 : 192.168.0.1/255.255.255.0
+ echo ifconfig br0 inet 192.168.0.1 netmask 255.255.255.0

Notice that when I'm prompted, the first character doesn't echo but is still saved in the variable.


Does anyone else see this same behavior? Any ideas on how to reset it back to how it works in STABLE? I'm not doing anything special with IFS so I'm stumped on how to troubleshoot this.
>How-To-Repeat:
	use the above script in 8-CURRENT and validate output when Enter/Return is hit on the keyboard when waiting for default values
>Fix:

	unknown


>Release-Note:
>Audit-Trail:
>Unformatted: