A user-defined variable is one whose value is assigned by a user. A sequence of optional parameter assignment lists and redirections, in any sequence. They are optionally followed by commands, words, and redirections. The value of a simple command is its exit status of zero if it terminates normally or nonzero if it terminates abnormally. The shell associates them with assigned values.
Wildcard characters are particularly useful when performing file name substitution.
A sequence of characters that does not contain any blanks. Words are separated by one or more metacharacters. Creating and Running a Shell Script Shell scripts provide an easy way to carry out tedious commands, large or complicated sequences of commands, and routine tasks. A shell script is a file that contains one or more commands. When you type the name of a shell script file, the system executes the command sequence contained by the file.