When do we need curly braces around shell variables?

Question

In shell scripts, when do we use {} when expanding variables?

For example, I have seen the following:

var=10        # Declare variable

         


        

Answer 1

The end of the variable name is usually signified by a space or newline. But what if we don't want a space or newline after printing the variable value? The curly braces tell the shell interpreter where the end of the variable name is.

Classic Example 1) - shell variable without trailing whitespace

TIME=10

# WRONG: no such variable called 'TIMEsecs'
echo "Time taken = $TIMEsecs"

# What we want is $TIME followed by "secs" with no whitespace between the two.
echo "Time taken = ${TIME}secs"

Example 2) Java classpath with versioned jars

# WRONG - no such variable LATESTVERSION_src
CLASSPATH=hibernate-$LATESTVERSION_src.zip:hibernate_$LATEST_VERSION.jar

# RIGHT
CLASSPATH=hibernate-${LATESTVERSION}_src.zip:hibernate_$LATEST_VERSION.jar

(Fred's answer already states this but his example is a bit too abstract)