= Shell Variables =

For a list of special variables are used internally by the shell, see [[Shell/ShellVariables|here]]. 

<<TableOfContents>>

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== Declaring ==

Variables are declared with an equals sign (`=`).

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

Note that variables can be set to an empty value, and this is distrinct from not being set.

{{{
d=
}}}

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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 argument tokens                      ||
||`$*`          ||all arguments as a single token          ||
||`$?`          ||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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