1 1 3.5 Shell Expansions 1 ==================== 1 1 Expansion is performed on the command line after it has been split into 1 'token's. There are seven kinds of expansion performed: 1 1 * brace expansion 1 * tilde expansion 1 * parameter and variable expansion 1 * command substitution 1 * arithmetic expansion 1 * word splitting 1 * filename expansion 1
1
· 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
1 command.
· Word Splitting How the results of expansion are split into separate
1 arguments.
· Filename Expansion A shorthand for specifying filenames matching patterns.
· Quote Removal How and when quote characters are removed from
1 words.
1
1 The order of expansions is: brace expansion; tilde expansion,
1 parameter and variable expansion, arithmetic expansion, and command
1 substitution (done in a left-to-right fashion); word splitting; and
1 filename expansion.
1
1 On systems that can support it, there is an additional expansion
1 available: PROCESS SUBSTITUTION. This is performed at the same time as
1 tilde, parameter, variable, and arithmetic expansion and command
1 substitution.
1
1 After these expansions are performed, quote characters present in the
1 original word are removed unless they have been quoted themselves (QUOTE
1 REMOVAL).
1
1 Only brace expansion, word splitting, and filename expansion can
1 change the number of words of the expansion; other expansions expand a
1 single word to a single word. The only exceptions to this are the
1 expansions of '"$@"' (⇒Special Parameters) and '"${NAME[@]}"'
1 (⇒Arrays).
1
1 After all expansions, 'quote removal' (⇒Quote Removal) is
1 performed.
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