Anyone know?: How the 'for'-loop could stop working in interactive bash shell?!

alex_5161 · #1 (**permalink**) 11-07-2008

It is happening with my sessions already second time: a 'for'-loop for some reason stop to work as expected.
That means or it is looping without exitting, or it is not loop even once.

Here example of my try when it is not processing even one loop.
You can see, I start new subshell and 'for' works fine, but returning back, the 'for' doesn't work again"

Code:

> for ((i=1;i<3;i++));do echo $i; done;
> echo mm
mm
> for ((i=1;i<3;i++));do echo $i; done;
> bash
executing file .bashrc - starting the bash shell--

----> Start of the .myset file  <---

  ----  It is SUN0 box with TEST and MODEL offices  ----

----> End   of the .myset file  <---
>
>
> for ((i=1;i<3;i++));do echo $i; done;
1
2
> 
> exit
exit
> for ((i=1;i<3;i++));do echo $i; done;
> echo boooo
boooo
>
>

Does anybody know what could be a reason?
I do not think it is related to connection soft (I use PuTTY.)

Appreciate any help or hint

Perderabo · #2 (**permalink**) 11-07-2008

Code:

bash-3.00$ for ((i=1;i<3;i++));do echo $i; done;
1
2
bash-3.00$ for ((i=1;i<3;i++));do echo $i; done;
1
2
bash-3.00$ for ((i=1;i<3;i++));do echo $i; done;
1
2
bash-3.00$ for ((i=1;i<3;i++));do echo $i; done;
1
2
bash-3.00$ for ((i=1;i<3;i++));do echo $i; done;
1
2
bash-3.00$ echo booo
booo
bash-3.00$ for ((i=1;i<3;i++));do echo $i; done;
1
2
bash-3.00$
bash-3.00$ for ((i=1;i<3;i++));do echo $i; done;
1
2
bash-3.00$

I can't reproduce your symptom. And I was using putty.

alex_5161 · #3 (**permalink**) 11-07-2008

It is correct, you can't reproduce it!
And I too, can not reproduce it!
I have this situation second time.
First time I have spend couple hours trying to realize what is wrong with my script, untill did not gess to try it in another session, where everything works fine.
Now some how it is happened again. Hopefully some time I could learn from past; so I have realized it shortly.
Now the session is oppened and I could make some test, if anybody would advice to try anything

As I have said, I have no idea how and why that is happening and that is my question, if anybody have any clue about that?!?!

Lakris · #4 (**permalink**) 11-07-2008

Hello,
this may be a long shot, but maybe You have an alias or something that is active in Your first shell (a login shell perhaps, that read .bash_login?) and the next shell is not a login shell and hence has some other definitions that overrule the first ones?
save output from alias and set from each shell and compare them. It maybe a lot of text but You said You wanted to understand...

use sort and -u on each file to narrow down size and then diff.

/Lakris

alex_5161 · #5 (**permalink**) 11-07-2008

Thanks Lakris.

Relation to login is not a reason, because a new connection has no problem originally. When that happened I di not know.

I have compared the aliases:

Code:

> alias >bad_alias
> !for
for ((i=1;i<3;i++));do ec $i; done;
>
>

In another session:

Code:

> for ((i=1;i<3;i++));do ec $i; done;
1
2
> alias>good_alias
>
>
> diff bad_alias good_alias
>                                    # so files are the same
>

Also I have saved result of 'typeset' and 'env'
Later will review (some function I could add, change during mork.)

But on first glance there is no real difference.

drl · #6 (**permalink**) 11-08-2008

Hi.

It might be useful to see how the shell is interpreting everything. Using set -x will show you the commands. This is from a vanilla bash called as sh:

Code:

$ set -x
+ set -x
sh-2.05b$ for ((i=1;i<3;i++));do echo $i; done;
+ (( i=1 ))
+ (( i<3 ))
+ echo 1
1
+ (( i++ ))
+ (( i<3 ))
+ echo 2
2
+ (( i++ ))
+ (( i<3 ))

cheers, drl

alex_5161 · #7 (**permalink**) 11-10-2008

Thank you, drl, set -x realy interesting thing.

It seems the shell some how do not processing assighment in the (( )).
Also in 'let' and in 'expr' ('ec' is an alianse for echo)

Code:

>ec $i; expr i++; ec $i
+ /usr/bin/echo 2
2
+ expr i++
i++
+ /usr/bin/echo 2
2
>ec $i; expr i++; expr i=1; ec $i
+ /usr/bin/echo 2
2
+ expr i++
i++
+ expr i=1
i=1
+ /usr/bin/echo 2
2
>ec $i; expr i++; let i=1; ec $i
+ /usr/bin/echo 2
2
+ expr i++
i++
+ let i=1
+ /usr/bin/echo 2
2
>ec $i; expr i++; i=1; ec $i
+ /usr/bin/echo 2
2
+ expr i++
i++
+ i=1
+ /usr/bin/echo 1
1
>ec $i; expr i++; i=$((i++)); ec $i
+ /usr/bin/echo 1
1
+ expr i++
i++
+ i=1
+ /usr/bin/echo 1
1
>

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