In Linux (Shell), there are two types of variable: (1) System variables - Created and maintained by Linux itself. This type of variable defined in CAPITAL LETTERS. (2) User defined variables (UDV) - Created and maintained by user. This type of variable defined in lower letters. Shell variables - var refers to the name, $var to the value - t = 100 #Sets var t to value 100 - echo ”$t = $t” #will print: $t = 100 - Remove a variable with unset var - Names begin with alpha characters and include alpha, numeric, or underscore
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A shell script is a computer program designed to be run by the Unix shell, a command-line interpreter. The various dialects of shell scripts are considered to be scripting languages. A shell usually interprets a single line of input, but we can also create a file containing a number of lines of commands to be interpreted. This file is a program known as a shell script. The program can also contain control structures (if-then, loops). Shell scripts allow a sequence of commands to be executed automatically .