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Variable Substitution in Shell

The name of a variable is a placeholder for its value, the data it holds. Referencing (retrieving) its value is called variable substitution.

Of Zeros and Nulls

 

              /dev/zero ... /dev/null

Uses of /dev/null

Think of /dev/null as a black hole. It is essentially the equivalent of a write-only file. Everything written to it disappears. Attempts to read or output from it result in nothing. All the same, /dev/null can be quite useful from both the command line and in scripts.

 

Arrays in Shell Scripting

 

                   Newer versions of Bash support one-dimensional arrays. Array elements may be initialized with the variable[xx] notation. Alternatively, a script may introduce the entire array by an explicit declare -a variable statement. To dereference (retrieve the contents of) an array element, use curly bracket notation, that is, ${element[xx]}.

List Constructs

 

                     The and list and or list constructs provide a means of processing a number of commands consecutively. These can effectively replace complex nested if/then or even case statements.