Declare variable(s) and/or give them attributes.
Syntax
declare [-afFirtx] [-p] [name[=value] ...]
typeset [-afFirtx] [-p] [name[=value] ...]
Key
-a Each name is an array variable.
-f Use function names only.
-F Inhibit the display of function definitions (implies -f)
only the function name and attributes are printed.
-i The variable is treated as an integer; arithmetic evaluation (see ARITHMETIC EVALUATION)
is performed when the variable is assigned a value.
-r Make names readonly. These names cannot then be assigned values by subsequent assignment
statements or unset.
-t Give each name the trace attribute.
Traced functions inherit the DEBUG and RETURN traps from the calling shell.
The trace attribute has no special meaning for variables.
-x Mark names for export to subsequent commands via the environment.
-p Display the attributes and values of each name.
When -p is used, additional options are ignored.
If no names are given then display the values of variables.
Using '+' instead of '-' turns off the attribute instead, e.g. +i means don’t treat as an integer - one exception is that +a can not be used to destroy an array variable.
When used in a function, makes each name local, as with the local command.
If a variable name is followed by =value, the value of the variable is set to value
The return value is 0 unless an invalid option is encountered, an attempt is made to define a function using '-f foo=bar', an attempt is made to assign a value to a readonly variable, an attempt is made to assign a value to an array variable without using the compound assignment syntax (see Arrays above), one of the names is not a valid shell variable name, an attempt is made to turn off readonly status for a readonly variable, an attempt is made to turn off array status for an array variable, or an attempt is made to display a non-existent function with -f.
If the extdebug shell option is enabled using shopt, the source file name and line number where the function is defined are displayed as well.
declare is a bash builtin command
“I have nothing to declare but my genius” ~ Oscar Wilde
for - Expand words, and execute commands.
while - Loop to execute commands.
until - Loop to execute commands.