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Base: Document Shell's variable indexing behaviour

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AnotherTest 2021-03-17 12:44:25 +03:30 committed by Andreas Kling
parent 6c94207ee0
commit 4ff430b615
Notes: sideshowbarker 2024-07-18 21:08:52 +09:00 
Author: https://github.com/alimpfard
Commit: https://github.com/SerenityOS/serenity/commit/4ff430b6152
Pull-request: https://github.com/SerenityOS/serenity/pull/5749
1 changed files with 15 additions and 2 deletions
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17
Base/usr/share/man/man5/Shell.md
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@ -45,7 +45,16 @@ Any sequence of _Double Quoted String Part_ tokens:
* Escaped sequences
##### Variable Reference
Any sequence of _Identifier_ characters, or a _Special Variable_ following a `$`
Any sequence of _Identifier_ characters, or a _Special Variable_ following a `$`.
Variables may be followed by a _Slice_ (see [Slice](#Slice))
##### Slice
Variables may be sliced into, which will allow the user to select a subset of entries in the contents of the variable.
An expression of the form $_identifier_[_slice-contents_] can be used to slice into a variable, where _slice-contents_ has semantics similar to _Brace Expansions_, but it may only evaluate to numeric values, that are used to index into the variable being sliced.
Negative indices are allowed, and will index the contents from the end. It should be noted that the shell will always perform bounds-checking on the indices, and raise an error on out-of-bound accesses. Slices can slice into both lists and strings.
For example, `$lst[1..-2]` can be used to select a permutation of a 4-element list referred to by the variable `lst`, as the slice will evaluate to the list `(1 0 -1 -2)`, which will select the indices 1, 0, 3, 2 (in that order).
##### Immediate Expressions
An expression of the form '${identifier expression...}', such expressions are expanded to other kinds of nodes before resolution, and are internal functions provided by the shell.
@ -452,13 +461,17 @@ dquoted_string_inner :: '\' . dquoted_string_inner? {concat}
| '\' 'x' digit digit dquoted_string_inner?
| '\' [abefrn] dquoted_string_inner?
variable :: '$' identifier
variable :: variable_ref slice?
variable_ref :: '$' identifier
| '$' '$'
| '$' '?'
| '$' '*'
| '$' '#'
| ...
slice :: '[' brace_expansion_spec ']'
comment :: '#' [^\n]*
immediate_expression :: '$' '{' immediate_function expression* '}'