variable interpolation in shell

问题:

This is probably a very basic question but for some reason I seem to be over looking the obvious.

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 back ticks 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 back ticks are intended for the expression evaluation

回答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.

回答2:

Use curly braces around the variable name:

`tail -1 ${filepath}_newstap.sh`

回答3:

In bash:

tail -1 ${filepath}_newstap.sh