weird behaviour of ((count++)) when using , , to change to lower case

[Andrew Benton]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' 
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-unknown-linux-gnu' 
-DCONF_VENDOR='unknown' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash' 
-DSHELL -DHAVE_CONFIG_H   -I.  -I. -I./include -I./lib   -g -O2
uname output: Linux eccles 2.6.35-rc6 #1 SMP Fri Jul 23 11:52:29 BST 2010 
x86_64 x86_64 x86_64 GNU/Linux
Machine Type: x86_64-unknown-linux-gnu

Bash Version: 4.1
Patch Level: 2
Release Status: release

Description:
Incrementing a variable with ((count++)), which should access the value 
in the variable and then increment it by 1 has some strange behaviour. 
In some situations it seems to increment the variable before accessing 
it, and in others it increments it by 2

Repeat-By:
Make an array to work with:

andy:~$ days=({Mon,Tues,Wednes,Thurs,Fri,Satur,Sun}day)
andy:~$ echo ${da...@]}
Monday Tuesday Wednesday Thursday Friday Saturday Sunday

So far, so good. Now try to access the array by stepping through it with
((count++))

andy:~$ count=0
andy:~$ echo ${days[$((count++))]}, ${days[$((count++))]}, 
${days[$((count++))]}
Monday, Tuesday, Wednesday

Also good. Now try converting it to lower case with ,,

andy:~$ count=0
andy:~$ echo ${days[${count}],,}, ${days[$((count++))],,}, 
${days[$((count++))],,}
monday, tuesday, thursday

What happened to wednesday?

Andy

Re: weird behaviour of ((count++)) when using , , to change to lower case

[Bernd Eggink]

Am 01.08.2010 13:06, schrieb Andrew Benton:


Also good. Now try converting it to lower case with ,,

andy:~$ count=0
andy:~$ echo ${days[${count}],,}, ${days[$((count++))],,}, 
${days[$((count++))],,}
monday, tuesday, thursday

What happened to wednesday?


I'd rather expect this to print monday, monday, tuesday, since you 
left out the ++ in the first term.


I think the problem is that the ,, operator causes each expression to be 
evaluated twice. That would explain this behaviour, and it's a bug IMHO.


Regards,
Bernd

--
Bernd Eggink
http://sudrala.de

Re: weird behaviour of ((count++)) when using , , to change to lower case

[Dennis Williamson]

If I do the echo line twice, I get a segfault in both Bash
4.0.33(1)-release and 4.1.0(1)-release.

And you're right about being evaluated twice.

On Sun, Aug 1, 2010 at 3:59 PM, Bernd Eggink mono...@sudrala.de wrote:
 Am 01.08.2010 13:06, schrieb Andrew Benton:

 Also good. Now try converting it to lower case with ,,

 andy:~$ count=0
 andy:~$ echo ${days[${count}],,}, ${days[$((count++))],,},
 ${days[$((count++))],,}
 monday, tuesday, thursday

 What happened to wednesday?

 I'd rather expect this to print monday, monday, tuesday, since you left
 out the ++ in the first term.

 I think the problem is that the ,, operator causes each expression to be
 evaluated twice. That would explain this behaviour, and it's a bug IMHO.

 Regards,
 Bernd

 --
 Bernd Eggink
 http://sudrala.de

basic pattern match Question...newbie doesn't understand (!...@#$@$)

[Linda Walsh]

I have:

w=/home/law/bin/package: line 5: type: xx: not found

The =~ operator is suppose to use the RH Expr as a ext.-regex.

So why doesn't this match and print not found?

if [[ $w =~ .*not found.* ]]; then echo not found; fi

It prints nothing.  Seems like such a basic concept.   Sorry, this newbie
needs help on such trivial matters. :-(


 echo $BASH_VERSION
4.0.35(1)-release

RFE? request for an undefined attribute for functions

[Linda Walsh]

I had(have) several functions that I don't use on a regular basis (rarely), that
I had put into a subdir func_lib under my local-definitions directory.
This came from ksh, which allows you to define functions with an undef 
attribute,
and at runtime, the first time these functions were referenced,

Is this something that might have been considered for bash?  It seems like it
could have some usefulness?

Re: basic pattern match Question...newbie doesn't understand (!...@#$@$)

[Chris F.A. Johnson]

On Sun, 1 Aug 2010, Linda Walsh wrote:


I have:

w=/home/law/bin/package: line 5: type: xx: not found

The =~ operator is suppose to use the RH Expr as a ext.-regex.

So why doesn't this match and print not found?

if [[ $w =~ .*not found.* ]]; then echo not found; fi

It prints nothing.  Seems like such a basic concept.   Sorry, this newbie
needs help on such trivial matters. :-(


   When quoted, the right-hand argument is matched as a string, not an
   expression.

--
   Chris F.A. Johnson, http://cfajohnson.com
   Author:
   Pro Bash Programming: Scripting the GNU/Linux Shell (2009, Apress)
   Shell Scripting Recipes: A Problem-Solution Approach (2005, Apress)