Symbol

Description

unset

Removes a variable

Example: removes a value of variable, without removing variable set the value to null

readonly

Makes the value of a variable permanent

Options:

n/a without an argument, it displays a list of all readonly shell variables

declare and typeset

Assigns an attributes to a variable #( with option but no variable names as arguments, the command lists all shell variables that have the indicated attributes set.)

Options:

-a declares a variable as an array

-f declares a variable to be a function name

-i declares a variable to be type integer

-r makes a variable readonly; also readonly

-x exports a variable (makes it global-all shells); also export

Examples:

export

and declare

Allows to create your own environmental variables (available to all child shells). To see exported variables in your shell type export with or wo option -p or declare -x.

printenv

Prints all or part of what is in environment (shows variable=values)

set

With no arguments or options will print all values of all variables know to the shell.

Options:

noclobber avoids overwriting files

noglob does not allow the use of wildards

nounset indicates an error when trying to use an undefined variable

vi enters vi editing mode

Example:

echo$<va- riable>

echo value of a variable

Options:

$ indicates that you wish to see the value contained in that variable

Example:

alias

Short name for a long or complex command. Syntax: alias [name[=value]]

Options:

n/a with no argument print the list of all aliases

Example:

unalias

Removes aliases