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bash: Shell Parameters
bash: Basic Shell Features
bash: Redirections
3.5 Shell Expansions
====================
Expansion is performed on the command line after it has been split into
'token's. There are seven kinds of expansion performed:
* brace expansion
* tilde expansion
* parameter and variable expansion
* command substitution
* arithmetic expansion
* word splitting
* filename expansion
· Brace Expansion Expansion of expressions within braces.
· Tilde Expansion Expansion of the ~ character.
· Shell Parameter Expansion How Bash expands variables to their values.
· Command Substitution Using the output of a command as an argument.
· Arithmetic Expansion How to use arithmetic in shell expansions.
· Process Substitution A way to write and read to and from a
command.
· Word Splitting How the results of expansion are split into separate
arguments.
· Filename Expansion A shorthand for specifying filenames matching patterns.
· Quote Removal How and when quote characters are removed from
words.
The order of expansions is: brace expansion; tilde expansion,
parameter and variable expansion, arithmetic expansion, and command
substitution (done in a left-to-right fashion); word splitting; and
filename expansion.
On systems that can support it, there is an additional expansion
available: PROCESS SUBSTITUTION. This is performed at the same time as
tilde, parameter, variable, and arithmetic expansion and command
substitution.
After these expansions are performed, quote characters present in the
original word are removed unless they have been quoted themselves (QUOTE
REMOVAL).
Only brace expansion, word splitting, and filename expansion can
change the number of words of the expansion; other expansions expand a
single word to a single word. The only exceptions to this are the
expansions of '"$@"' (
Special Parameters) and '"${NAME[@]}"'
(Arrays).
After all expansions, 'quote removal' (Quote Removal) is
performed.