Shell Programming and Scripting

Originally Posted by Don Cragun

Sorry. I just do not believe you.

If I run the following commands sequentially in an interactive shell that uses Bourne shell syntax:

Code:

$ XYZ=abc
$ echo "$XYZ"
abc
$ echo '$XYZ'
$XYZ
$ echo "XYZ is set to '$XYZ'"
XYZ is set to 'abc'
$

I get the output shown in bold text from those commands. And, if I put the commands in a script:

Code:

XYZ=abc
echo "$XYZ"
echo '$XYZ'
echo "XYZ is set to '$XYZ'"

and execute it, I get the output:

Code:

abc
$XYZ
XYZ is set to 'abc'

If you use a shell that uses csh syntax instead of Bourne shell syntax, you still get the same results if you change the 1st command from:

Code:

XYZ=abc

to:

Code:

set XYZ=abc

The only way that the command:

Code:

grep '$XYZ' file

and the command:

Code:

grep "$XYZ" file

produce the same, non-empty output is if the variable XYZ has been set with something like:

Code:

XYZ='$XYZ'

(assuming Bourne shell syntax) or:

Code:

set XYZ='$XYZ'

(assuming csh shell syntax) and the file named file contains the literal string $XYZ unless you have a function named grep, an alias for grep, or a non-standard version of the grep utility that is found in your PATH environment variable before the standard version of the grep utility.