= Bash Variables =

For a list of special variables are used internally by the `bash(1)` shell, see [[Bash/ShellVariables|here]]. 

<<TableOfContents>>

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== Declaring ==

Variables can be explicitly declared with the `declare` [[Bash/BuiltinCommands#Declare|builtin]].

{{{
declare a=1 b=2 c=3
}}}

A variable can be declared without a value, and this is distinct from not being set.

{{{
declare d
}}}

Variables can also be created implicitly.

{{{
a=1
b=2
c=3
}}}

And as with `declare`, variables can be set empty.

{{{
d=
}}}

For declaring array variables, see [[Bash/Array|here]].

Within a function, [[Bash/Function#Local_Scope|local variables]] can be declared with the `local` [[Bash/BuiltinCommands#Local|builtin]].

{{{
local a=1 b=2 c=3
}}}

Note that if `declare` is used within a function, those variables are also locally-scoped.

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== Usage ==

Variables are accessed by their name. A dollar sign (`$`) must be prefixed to the name.

{{{
a=foo
b=$a       # 'foo'
}}}

To delimit a variable name from string literals, use braces. For example:

{{{
a=foo
b=${a}bar  # 'foobar'
}}}

If a variable's value includes a character that the shell will interpret specially, [[Bash/Quoting|quote]] the variable.

{{{
a=foo
b="$a bar" # 'foo bar'
}}}

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== Special Variables ==

The following variables are set automatically by `bash(1)`.

||'''Variable'''||'''Value'''                              ||
||`$#`          ||number of arguments                      ||
||`$@`          ||all arguments as an [[Bash/Array|array]] ||
||`$*`          ||all arguments as a string                ||
||`$?`          ||the exit code                            ||
||`$$`          ||the PID of the shell                     ||
||`$!`          ||the PID of the most recent background job||



=== Positional Variables ===

The name of a command is stored in `$0`.

The first argument to the command is stored in `$1`. And so on until the 9th argument, `$9`.

From the tenth argument, while arguments are stored in an indexed variable, they must be accessed differently. `$10` is interpretted like `${1}0`. To actually access the 10th argument, try `${10}`.



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