>To: Jim Plank <plank@cs.utk.edu>
>Subject: Executing commands in shells
>
>Dr. Plank,
>	Sorry for this question but I'm having a hard time figuring exactly 
>what's happening in the following shell scenario
>
>Wael on duncan> sh 
>$ grep '\<for\>' /usr/dict/words 
>for 
>$ c="grep '\<for\>' /usr/dict/words"  
>$ echo $c 
>grep '\<for\>' /usr/dict/words 
>$ t="`$c`"  
>$ echo $t
>
>$ t=`"$c"` 
>grep '\<for\>' /usr/dict/words: not found
>
>
>Now the questions :
>1- Why in  t="`$c`" do I get nothing as the output in $t ?
>2- Why in  t=`"$c"` do I get an error ?
>3- If these two syntaxes are wrong, what's the right way of doing the 
>above (storing the command in a string then executing the string and 
>directing the output to another string) ?

I can't answer the why part of it.  It's the quotes that
are throwing the shell off:

$ b='grep \<for\> /usr/dict/words'
$ echo $b
grep \<for\> /usr/dict/words
$ $b
for

Evidently when you execute a shell command from a variable, you don't have
to worry about quoting:

$ a='"'
$ echo $a
"
$ 

Oddly, though, there are some metacharacters that do matter, like *:

$ ls *.ps
labs.ps
$ c='ls *.ps'
$ $c  
labs.ps
$ 

If you're sick of trying alternatives, and want some cheap fixes, you 
can use  "sh -c" or just pipe your command with quotes to the shell:

$ grep '\<for\>' /usr/dict/words
for
$ c="grep '\<for\>' /usr/dict/words"
$ echo $c
grep '\<for\>' /usr/dict/words
$ sh -c "$c"
for
$ echo $c | sh
for
$ 

Hope that helps,

Jim