Curly braces in bash allow script to see variable?

[jouell]

#!/bin/bash
set -u

ls /etc

{

ls /

SUBJECT=TEST

} | mail -s "$SUBJECT" $ME

This returns "unbound variable" or just a blank subject w/o set -u. I thought the commands/script outside of the curly braces can see the variable $SUBJECT as it's supposed to be global.

I am missing something basic here.

Thanks!
jouell

 

[feherke]

Hi

I thought the commands/script outside of the curly braces can see the variable $SUBJECT as it's supposed to be global.

Yes, just a simple pair of braces ( {} ) does nothing special :

[blue]master #[/blue] { foo=bar; }; echo "~$foo~"
~bar~

But if the brace delimited block's output is piped, the block will be executed in a sub-process and nothing set there will be ever visible to the outside :

[blue]master #[/blue] { foo=bar; } | echo "~$foo~"
~~

The solution is to use process substitution instead of piping :

[blue]master #[/blue] { foo=bar; } > >( echo "~$foo~" )
~bar~

Process substitutions is available in Bash and Ksh, but not in the original Bourne shell.


Feherke.

 

[jouell]

Feherke,

Thanks so much. Exactly Right. After you posted I researched that and found some links that are helpful in learning more:

http://tldp.org/LDP/abs/html/process-sub.html

http://www.linuxprogrammingblog.com/pipe-in-bash-can-be-a-trap

Thanks!!
jouell

 

[jouell]

I wonder if I spoke too soon on this, doing as suggested on the cmd line is OK, but as a shell script seems not working?

OK:

# { foo=bar; } > >( echo "~$foo~" )
# ~bar~

# cat i
#!/bin/bash
{ foo=bar; } > >( echo "~$foo~" )

Neither of these work:

#bash i
~~

#./i
~~

# bash -x  i
+ foo=bar
++ echo '~~'
~~

 

[feherke]

Hi

Hmm... There must be some issue with the expansion order. The variable survives and is available outside the braces, but not in the substituted process. Strange, the documentation mentions nothing about such restriction.

By the way, do you really need to set that variable inside the braces ?


Feherke.

 

[jouell]

Hi Feherke

>>By the way, do you really need to set that variable inside the braces ?

Not a must, I can work around it.

What I'm really trying to do is this:

{

comand1
...
comandX

if something good; then

SUBJECT=OK

else

SUBJECT=NOTOK

fi

} mail -s $SUBJECT


I could redirect out to a file and send it separately w/the subject but I'd really like to make this clean and efficient.

jouell

 

[feherke]

Hi

Unless that "something good" means running commands who's output has to be also included in the mail, I would prefer tho move the [tt]if[/tt] statement out from the brace block.

Sorry, tried some combinations, but none seems to work from a script.


Feherke.

 

[jouell]

Hi Feherke


Right those commands need to be included in the email. I can rewrite the script w/a temp file.

Thanks for looking here!
jouell