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possible compgen bug


From: Nicholas Mc Guire
Subject: possible compgen bug
Date: Fri, 9 May 2008 07:00:10 -0800 (AKDT)

HI !

problem: compgen assigns first option on receiving an empty string as
         input (i.e. by read -t 5 VAR  timing out)

systems and OS:

X86 (Duron and Sempron)

Debian etch:
address@hidden:~/shell$ uname -a
Linux backup 2.6.18-hpt374 #4 SMP Thu Mar 20 00:07:28 CET 2008 i686
GNU/Linux
address@hidden:~/shell$ bash --version
GNU bash, version 3.1.17(1)-release (i486-pc-linux-gnu)
Copyright (C) 2005 Free Software Foundation, Inc.

Slackware 10.0:
address@hidden:~/fipsi# uname -a
Linux rtl14 2.4.26 #6 Mon Jun 14 19:07:27 PDT 2004 i686 unknown unknown
GNU/Linux
address@hidden:~/fipsi# bash --version
GNU bash, version 2.05b.0(1)-release (i486-slackware-linux-gnu)
Copyright (C) 2002 Free Software Foundation, Inc.

both systems show the same (supposedly wrong) behavior of the compgen
builtin function.


corect behavior:
----------------

when using read with a timeout and then evaluating a variable I get the
following expected behavior:

#! /bin/bash

read -p "timeout 5 > " -t 5 CMD

if [ "$CMD"x == exitx ] ; then
   echo exiting
   $CMD
elif [ "$CMD"x == quitx ] ; then
   echo quite not a valid command calling exit with -1
   exit -1
else
   echo invalid command - exiting with -2
   exit -2
fi

which gives me the expected response when it times out due to no input

address@hidden:~/shell$ ./1.sh
timeout 5 > invalid command - exiting with -2
address@hidden:~/shell$


probably errornous behavior:
----------------------------

when using compgen to allow shortcuts (in the below example for quit and
exit I get a strange behavior when no input is entered and write times
out after 5 seconds:

#! /bin/bash

read -p "timeout 5 > " -t 5 FOO
CMD=( $(compgen -W "quit exit" -- $FOO) )

if [ "$CMD"x == exitx ] ; then
   echo exiting
   $CMD
elif [ "$CMD"x == quitx ] ; then
   echo quit not a valid command calling exit with -1
   exit -1
else
   echo invalid command - exiting with -2
   exit -2
fi

address@hidden:~/shell$ ./2.sh
timeout 5 > quit not a valid command calling exit with -1
address@hidden:~/shell$

it seems to expand CMD to quit - not the behavior I expected

I assume that this is a bug in compgen as it indentifies an empty string
with the first word in the options passed - I would have expected it to be
a null-string (just as if one would type x, which has no match, thus the
null-string is assigned to CMD)

thx!
hofrat




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