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docs: A bit on index ranges

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Try to make list-ness more accessible.
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Fabian Homborg
2021-05-12 19:30:56 +02:00
parent 127eaded96
commit 678fa2e6a9
1 changed files with 9 additions and 4 deletions
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doc_src/language.rst
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@@ -714,11 +714,16 @@ Because :ref:`$PATH <path>` is a list, this expands to all the files in all the
Index range expansion
^^^^^^^^^^^^^^^^^^^^^
Sometimes it's necessary to access only some of the elements of a list, or some of the lines a command substitution outputs. Both are possible in fish by writing a set of indices in brackets, like::
Sometimes it's necessary to access only some of the elements of a :ref:`list <variables-lists>` (all fish variables are lists), or some of the lines a :ref:`command substitution <expand-command-substitution>` outputs. Both are possible in fish by writing a set of indices in brackets, like::
$var[2]
# or
$var[1..3]
# Make $var a list of four elements
set var one two three four
# Print the second:
echo $var[2]
# prints "two"
# or print the first three:
echo $var[1..3]
# prints "one two three"
In index brackets, fish understands ranges written like ``a..b`` ('a' and 'b' being indices). They are expanded into a sequence of indices from a to b (so ``a a+1 a+2 ... b``), going up if b is larger and going down if a is larger. Negative indices can also be used - they are taken from the end of the list, so ``-1`` is the last element, and ``-2`` the one before it. If an index doesn't exist the range is clamped to the next possible index.