Good Habit #4: Quote variables with caution

Always be careful with shell expansion and variable names. It is generally a good idea to enclose variable calls in double quotation marks, unless you have a good reason not to. Similarly, if you are directly following a variable name with alphanumeric text, be sure also to enclose the variable name in curly braces ({}) to distinguish it from the surrounding text. Otherwise, the shell interprets the trailing text as part of your variable name -- and most likely returns a null value.

Listing 1 provides examples of various quotation and non-quotation of variables and their effects.

Listing 1. Example of good habit #4: Quoting (and not quoting) a variable

~ $ ls tmp /a b ~ $ VAR="tmp/*" ~ $ echo $VAR tmp/a tmp/b ~ $ echo "$VAR"  tmp/* ~ $ echo $VARa   ~ $ echo "$VARa" ~ $ echo "${VAR}a" tmp/*a ~ $ echo ${VAR}a tmp/a ~ $

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