diff options
| -rw-r--r-- | Base/usr/share/man/man5/Shell.md | 17 |
1 files changed, 15 insertions, 2 deletions
diff --git a/Base/usr/share/man/man5/Shell.md b/Base/usr/share/man/man5/Shell.md index 4a04ec9e25..896ddba8e6 100644 --- a/Base/usr/share/man/man5/Shell.md +++ b/Base/usr/share/man/man5/Shell.md @@ -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* '}' |