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Chet Ramey
54 lines
2.1 KiB
Plaintext
54 lines
2.1 KiB
Plaintext
This describes how bash users create, destroy, assign, and reference array
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variables. Array variables are variables whose values are arrays of strings,
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and whose elements may be referenced individually.
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CREATING
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- any variable may be declared as an array using `typeset -a'
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- an ordinary variable may be converted to an array using
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`typeset -a'; the value becomes array[0]
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- there is a question of notation used to simultaneously declare
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an array variable and populate it with values sequentially,
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like ksh does with `set -A'. `set -A' is a horrible choice;
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it should be discarded immediately.
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- we can use `typeset -a array [values...]'
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DESTROYING
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- `unset name' will destroy the array `name'
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- how to treat `typeset +a array'?
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- I think we should keep the variable, convert it from an
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array to an `ordinary' variable, and make the value at
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the smallest index of the array the value of the new
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variable
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ASSIGNING
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- array[index]=value will serve to assign values to individual
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elements of the array
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- the subscript can be an arbitrary arithmetic expression; it
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will be run through the expression evaluator
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- this can create arrays, too
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- this is analogous to defining a variable by simply
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assigning to it
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REFERENCING
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- $array will expand to all elements of the array, just like $*
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expands to all the positional parameters
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- "$array" is like "$@"
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- ${array[index]} is used to reference array element `index', where
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`index' can be an arbitrary arithmetic expression
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- two special values for `index': * and @ expand to all
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elements of the array, just like $* and $@. Quoting
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behavior is the same, too
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- using a subscript is an error if a variable has not been declared
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as an array (is this wise?)
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- ${#variable}, if `variable' is an array, expands to the number of
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elements in the array
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- ${#variable[n]} expands to the length of variable[n]. n
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may be an arbitrary arithmetic expression
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- ${#variable[*]} and ${#variable[@]} expand to the number of
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elements in the array
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OPEN QUESTIONS
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- should we allow them to be exported? Ksh does not, but rc does
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