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author | 2012-07-23 20:46:45 +0800 | |
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committer | 2012-07-24 03:56:34 +0530 | |
commit | 81e0342bf6b29fb0cebc726c6741deb82c3f1c23 (patch) | |
tree | fba9c5c5d668ddd956c733a847d24e2e67f7034a /doc_src | |
parent | 56599621ccfd06587eefff67b6713d428bcddbd0 (diff) |
index range doc
Diffstat (limited to 'doc_src')
-rw-r--r-- | doc_src/index.hdr.in | 52 |
1 files changed, 51 insertions, 1 deletions
diff --git a/doc_src/index.hdr.in b/doc_src/index.hdr.in index 84ed5a55..34ed91cb 100644 --- a/doc_src/index.hdr.in +++ b/doc_src/index.hdr.in @@ -80,7 +80,7 @@ while '-f' will turn it off. \subsection quotes Quotes -Sometimes features such as <a href="#globbing">parameter expansion</a> +Sometimes features such as <a href="#expand">parameter expansion</a> and <a href="#escapes">character escapes</a> get in the way. When that happens, the user can write a parameter within quotes, either ' (single quote) or " (double quote). There is one important difference @@ -581,6 +581,9 @@ A command substitution will not change the value of the <a href='#variables-status'>status</a> variable outside of the command substitution. +Only part of the output can be used, see <a href='#expand-index-range'>index +range expansion</a> for details. + Example: The command <code>echo (basename image.jpg .jpg).png</code> will @@ -674,6 +677,50 @@ element of the foo variable should be dereferenced and never that the fifth element of the doubly dereferenced variable foo. The latter can instead be expressed as $$foo[1][5]. +\subsection expand-index-range Index range expansion + +Both command substitution and environment variables support accessing only +specific items by providing a set of indices in square brackets. It's +often needed to access a sequence of elements. To do this, one can use +range operator '..' for this. A range 'a..b', where range limits 'a' and 'b' +are integer numbers, is expanded into a sequence of indices +'a a+1 a+2 ... b' or 'a a-1 a-2 ... b' depending on which of 'a' or 'b' +is higher. The negative range limits are calculated from the end of the array +or command substitution. + +Some examples: +<pre> +# Limit the command substitution output +echo (seq 10)[2..5] # will use elements from 2 to 5 +# Output is: +# 2 3 4 5 + +# Use overlapping ranges: +echo (seq 10)[2..5 1..3] # will take elements from 2 to 5 and then elements from 1 to 3 +# Output is: +# 2 3 4 5 1 2 3 + +# Reverse output +echo (seq 10)[-1..1] # will use elements from the last output line to the first one in reverse direction +# Output is: +# 10 9 8 7 6 5 4 3 2 1 +</pre> + +The same works when setting or expanding variables: +<pre> +# Reverse path variable +set PATH $PATH[-1..1] +# or +set PATH[-1..1] $PATH + +# Use only n last items of the PATH +set n -3 +echo $PATH[$n..-1] +</pre> + +NOTE: Currently variables are allowed inside variables index expansion, but not in indices, +used for command substitution. + \subsection expand-home Home directory expansion The ~ (tilde) character at the beginning of a parameter, followed by a @@ -909,6 +956,9 @@ If you specify a negative index when expanding or assigning to an array variable, the index will be calculated from the end of the array. For example, the index -1 means the last index of an array. +A range of indices can be specified, see <a href='#expand-index-range'>index +range expansion</a> for details. + \subsection variables-special Special variables The user can change the settings of \c fish by changing the values of |