Shell Programming and Scripting

thank you

It depends what you have defined for the variable var, which appears to be a file name. Would you be trying to effectively call in some other code here? What's wrong with just making the file executable and running it, i.e.

Code:

echo "About to run my sub-script in $var"
$var
echo "Finished running sub-script in $var"

Apologies if I have misunderstood, but you may just be over thinking your puzzle.

Of course, if you are setting values in your sub-script that you want to remain for your calling script, you would code it like this (for ksh):-

Code:

echo "About to run my sub-script in $var"
. $var
echo "Finished running sub-script in $var"

Robin

thank you

Why not just source it? . /path/to/filename

This runs it inside your own shell line-by-line.

thank you

Why not source the temp file, then?

It's not a question of how eval works, it's a question of how the shell works. When a string is unquoted, it splits on all whitespace, not lines.

Using eval means the string gets split twice -- once when you feed it into eval, and again when eval actually executes the code you give it.

What is the echo for? Do you want eval to print those statements or run them?

I think eval "$(cat file)" is closest to what you want... But again I strongly question whether you need eval at all. I bet you could have avoided it if you'd known that using a pipe there would paint you into a corner.

I thought I knew what you were trying to do, but now I'm completely lost. In your original message you said you wanted to know the difference between:

Code:

eval echo "`cat $var`"

and:

Code:

eval echo "\"`cat $var`\""

There is a very easy way to see the difference. Set var to be the name of a file that contains:

Code:

echo "this is step 1"
date

and then run the commands. In the first case, the output will be:

Code:

echo this is step 1
Thu Apr 25 11:47:54 PDT 2013

modified to be the date corresponding to when you run it and your setting of the TZ environment variable. In the second case, the output will be:

Code:

echo this is step 1
date

So, the difference is that in one, the date command is executed and in the other it is not. And this is explained by the fact that you escaped one set of double quotes in the 2nd eval.

But, this has nothing to do with pipes nor directing the output to a temp file. You can redirect or pipe the output of an eval command and you can redirect or pipe the output of a source (.) command the same way.

I think you need to restate what you are trying to do with pipes and temp files, show us what you're doing, show us what results you're getting, and show or tell us how the results you want are different from what you're getting.