Question

Would you please explain why the following shell command wouldn’t work:

sh-3.1$ echo $MYPATH
/opt/Application/DATA/CROM/my_application
sh-3.1$ awk '{print substr($MYPATH,3)}'

Thanks
Best Regards

Answer 1

MYPATH is not going to be substituted by the shell since the string uses single quotes. Consider the following:

csh$ echo '{print substr($USER,3)}'
{print substr($USER,3)}
csh$ echo "{print substr($USER,3)}"
{print substr(dshawley,3)}

The usage of single quotes instructs the shell to pass the string argument to the program as-is. Double quotes tell the shell to perform variable expansion on the argument before passing it to the program. This is a basic shell feature that is common amongst shells and some programming languages (e.g., perl).

The next problem that you are going to run into is that awk will want quotes around the first parameter to substr or the parse will fail. You will probably see an “Illegal variable name” warning in this case. This is where I get lost with csh since I have no clue how to properly escape a double-quote within a quoted string. In bash/sh/ksh, you would do the following:

sh$ awk "{print substr(\"$USER\",3)}"
input
^D
hawley
sh$

Just in case you do not already know this, awk will require an input stream before it is going to do anything. I had to type “input” and the EOF character for the little example.