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→Using Variables in Shell Scripts
''<b>User-defined variables</b> are variables which can be '''created by the user''' and exist in the session. This means that no one can access user-defined variables that have been set by another user,<br>and when the session is closed these variables expire.''<br>'''Reference:''' https://mariadb.com/kb/en/user-defined-variables/
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Data can be stored and removed within a variable using an '''equal sign'''.<br>The '''read''' command can be used to prompt the user to enter data into a variable.<br>Refer to the diagram on the right-side to see how user-defined variables are assigned data.
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'''Positional Parameters and Special Parameters'''
[[Image:positional.png|thumb|right|220px|Examples of using '''positional''' and '''special''' parameters.]]A '''positional parameter''' is a variable within a shell program; its value is set from an argument specified on the command line that invokes the program.
Positional parameters are numbered and their values are referred to with accessed by using a preceding "'''$'''": (eg. '''$1''', '''$2''', '''$3''', and so on. The positional parameter $0 refers to either the name of shell where command was issued, or name of shell script being executed. If using '''positional parameters''' greater than '''9''', then you need to include number within braces.<br>Examples: '''echo ${10}''', '''ls ${23}'''
The '''shift''' command can be used with positional parameters to shift positional parameters<br>to the left by one or more positions.
