Shell Programming and Scripting

thank you

I'm still confused what you are trying to actual do here.

I still think you would be better sourcing your file from you script.

Let me put it like this:-
my_env.ksh

Code:

#!/bin/ksh
a=Hello
b=Robin
c="$a $b"
echo "$c"

my_script.ksh

Code:

#!/bin/ksh
echo "Starting my script."
echo "$c"
. my_env.ksh          # I'm assuming that this is in your $PATH
echo "I have set up the environment within this shell."
echo "My name is $b"
echo "$a world!"

Then I can run

Code:

$ echo $a

$ my_script.ksh
Starting my script.

Hello Robin
I have set up the environment within this shell.
My name is Robin
Hello world!
$

You can see that the values of $a, $b & $c are available to your calling script. They way you have it with eval leaves you open to odd things, such as your echo with quotes. Calling

Code:

eval echo "echo "this is line 1"
                 date"

.... will just confuse things because it will try to match up quote etc. , so you are actually going to execute:-

Code:

echo echo this is line 1"
"

which will work, but is a bit odd. How would you cope with multiple / escaped quotes? Consider odd_file

Code:

echo "This is the 
\"text\"
...I think"

An eval of that might go a bit wild. If you run this on the command line:-

Code:

$ while read line
> do
>    eval $line
> done < odd_file
This is the
ksh[3]: text:  not found
ksh[3]: ...I:  not found

Where you could:-

Code:

$ ksh odd_file
This is the 
"text"
...I think

or

Code:

$ . odd_file 
This is the 
"text"
...I think

Perhaps I am being stupid and not seeing what you have explained. Can you be very direct as to the purpose. I don't mind how terse you make the language, I'm just very confused.


Robin

I repeat: What pipe are you talking about? There is no pipe in the above command line. The || indicates that this is an AND-OR list; not a pipeline. As some of us have said several times, for what you are doing here, it would be MUCH MUCH simpler if you would use the command:

Code:

. "$filevar" > "$file_var_sql" || die "error comment"

instead of trying to use eval. If you would source the file instead of trying to evaluate it, you would much more easily understand what is going on since there is a single execution of the contents of the file without having to worry about how multiple levels of command substitution and quote removal will be processed.

The output from either . (in the line above) or eval (in your line of code) produce output that can be redirected to a file (in this case named by $file_var_sql) that can can be made to contain commands that can be executed later.

THERE IS NO NEED TO USE EVAL IN THIS CASE. USING EVAL IN THIS CASE JUST MAKES YOUR CODE HARDER TO READ and HARDER TO UNDERSTAND.
I guess I am a poor teacher. I don't see how repeating what I said in numerous other posts in this thread that show you step by step the process the shell goes through to produce exactly the output that you see when you run both of these commands is going to help. You don't need eval for this and your fixation on eval rather than using simpler equivalent tools (. in this case) for this project doesn't make sense.
No. You won't have an eval in the intermediate results of running eval.

I'm sorry I have been unable to explain this to you. If the step by step analysis of the process the shell goes through to process these commands in messages #14, #16, and #21 in this thread isn't clear, I don't know how to help.

Sorry,
Don

In other words, don't use eval here.
It is used to build up and run command lines, and to simulate pointer variables. First the shell scans the line and passes it to eval. Then eval executes the line, including scanning the line again. That's how it works.

I've written many shell scripts, have rarely or never had to use eval. I would focus on other things more useful, less confusing.

thank you

This is probably the main bone of contention here. Depriving us of this information had us building solutions that wouldn't ever work for you because of incomplete information. "But I need eval!" "No you don't, try this!" "It didn't work, see I need eval!" "What didn't work? What did it do?" "How do I use eval?"

Show us the data and we'll get it straightened out much faster. That still doesn't necessarily mean you need eval. There's ways without eval to set arbitrary variable names, if you even need that.

Show the contents of this sql file please (with anything confidential blanked).

Well, you do seem to have your reasons for wanting to eval rather than to source the script. I don't think we will "get mad", more just very confused at what you are trying to achieve. Perhaps it is us that is not understanding. Can you paste in a small section of your file that you want eval to work on? Try to keep it to the smallest unit of work. Leave out anything sensitive but make it obvious when you do so.

For the calling script, it would be best to keep that very small too, so we can focus on a specific issue, rather than a big script.

If it is something like:-

My script is:-
eval "`cat my_deck.sql

Code:

sqlplus -S ${username}/${password}@${ora-SID} @my_deck.sql

.... or

Code:

sqlplus / <<-EOSQL
select * from user_tables;
EOSQL

.... then you can still source that in. Perhaps if we see what you really want to execute, then perhaps we will better understand and not wonder why you don't source it in.


I'm sure there are things I will not have considered so I too am happy to learn.




Robin