bash - Variable interpolation in the shell

Question

I have a variable called filepath=/tmp/name.

To access the variable, I know that I can do this: $filepath

In my shell script I attempted to do something like this (the backticks are intended)

`tail -1 $filepath_newstap.sh`

This line fails, duuh!, because the variable is not called $filepath_newstap.sh

How do I append _newstap.sh to the variable name?

Please note that backticks are intended for the expression evaluation.

Answer 1

Use

"$filepath"_newstap.sh

or

${filepath}_newstap.sh

or

$filepath\_newstap.sh

_ is a valid character in identifiers. Dot is not, so the shell tried to interpolate $filepath_newstap.

You can use set -u to make the shell exit with an error when you reference an undefined variable.