diff options
Diffstat (limited to 'Doc/Zsh/expn.yo')
| -rw-r--r-- | Doc/Zsh/expn.yo | 60 |
1 files changed, 38 insertions, 22 deletions
diff --git a/Doc/Zsh/expn.yo b/Doc/Zsh/expn.yo index 416d46407..0c26a7ca5 100644 --- a/Doc/Zsh/expn.yo +++ b/Doc/Zsh/expn.yo @@ -588,23 +588,29 @@ remove the non-matched elements). xitem(tt(${)var(name)tt(:)var(offset)tt(})) item(tt(${)var(name)tt(:)var(offset)tt(:)var(length)tt(}))( This syntax gives effects similar to parameter subscripting -in the form tt($)var(name)tt({)var(offset)tt(,)var(end)tt(}) but in -a form compatible with other shells. - -If the variable var(name) is a scalar, substitute the contents -starting from offset var(offset); if var(name) is an array, -substitute elements from element var(offset). If var(length) is -given, substitute that many characters or elements, otherwise the -entire rest of the scalar or array. - -var(offset) is treated similarly to a parameter subscript: -the offset of the first character or element in var(name) -is 0 if the option tt(KSH_ARRAYS) is set, else 1; a negative -subscript counts backwards so that -1 corresponds to the last -character or element. +in the form tt($)var(name)tt({)var(start)tt(,)var(end)tt(}), but is +compatible with other shells; note that both var(offset) and var(length) +are interpreted differently from the components of a subscript. + +If var(offset) is non-negative, then if the variable var(name) is a +scalar substitute the contents starting var(offset) characters from the +first character of the string, and if var(name) is an array substitute +elements starting var(offset) elements from the first element. If +var(length) is given, substitute that many characters or elements, +otherwise the entire rest of the scalar or array. + +A positive var(offset) is always treated as the offset of a character or +element in var(name) from the first character or element of the array +(this is different from native zsh subscript notation). Hence 0 +refers to the first character or element regardless of the setting of +the option tt(KSH_ARRAYS). + +A negative offset counts backwards from the end of the scalar or array, +so that -1 corresponds to the last character or element, and so on. var(length) is always treated directly as a length and hence may not be -negative. +negative. The option tt(MULTIBYTE) is obeyed, i.e. the offset and length +count multibyte characters where appropriate. var(offset) and var(length) undergo the same set of shell substitutions as for scalar assignment; in addition, they are then subject to arithmetic @@ -615,19 +621,29 @@ print ${foo: 1 + 2} print ${foo:$(( 1 + 2))} print ${foo:$(echo 1 + 2)}) -all have the same effect. +all have the same effect, extracting the string starting at the fourth +character of tt($foo) if the substution would otherwise return a scalar, +or the array starting at the fourth element if tt($foo) would return an +array. Note that with the option tt(KSH_ARRAYS) tt($foo) always returns +a scalar (regardless of the use of the offset syntax) and a form +such as tt($foo[*]:3) is required to extract elements of an array named +tt(foo). -Note that if var(offset) is negative, the tt(-) may not appear immediately +If var(offset) is negative, the tt(-) may not appear immediately after the tt(:) as this indicates the -tt(${)var(name)tt(:-)var(word)tt(}) form of substitution; a space +tt(${)var(name)tt(:-)var(word)tt(}) form of substitution. Instead, a space may be inserted before the tt(-). Furthermore, neither var(offset) nor var(length) may begin with an alphabetic character or tt(&) as these are -used to indicate history-style modifiers. +used to indicate history-style modifiers. To substitute a value from a +variable, the recommended approach is to proceed it with a tt($) as this +signifies the intention (parameter substitution can easily be rendered +unreadable); however, as arithmetic substitution is performed, the +expression tt(${var: offs}) does work, retrieving the offset from +tt($offs). For further compatibility with other shells there is a special case -when the tt(KSH_ARRAYS) option is active, as in emulation of -Bourne-style shells. In this case array subscript 0 usually refers to the -first element of the array. However, if the substitution refers to the +for array offset 0. This usually accesses to the +first element of the array. However, if the substitution refers the positional parameter array, e.g. tt($@) or tt($*), then offset 0 instead refers to tt($0), offset 1 refers to tt($1), and so on. In other words, the positional parameter array is effectively extended by |