From ff3e47e9f4fdde30512f48a4e11b2bbaee0c22a3 Mon Sep 17 00:00:00 2001 From: Peter Stephenson Date: Tue, 10 Oct 2017 09:59:31 +0100 Subject: 41842: aliasing documentation update --- Doc/Zsh/grammar.yo | 38 +++++++++++++++++++++++++++++--------- 1 file changed, 29 insertions(+), 9 deletions(-) (limited to 'Doc/Zsh/grammar.yo') diff --git a/Doc/Zsh/grammar.yo b/Doc/Zsh/grammar.yo index 463ac8831..bd7727298 100644 --- a/Doc/Zsh/grammar.yo +++ b/Doc/Zsh/grammar.yo @@ -568,15 +568,6 @@ itemiz(With global aliasing, any command separator, any redirection operator, and `tt(LPAR())' or `tt(RPAR())' when not part of a glob pattern) enditemize() -It is not presently possible to alias the `tt(LPAR()LPAR())' token that -introduces arithmetic expressions, because until a full statement has been -parsed, it cannot be distinguished from two consecutive `tt(LPAR())' -tokens introducing nested subshells. - -When tt(POSIX_ALIASES) is set, only plain unquoted strings are eligible -for aliasing. The tt(alias) builtin does not reject ineligible aliases, -but they are not expanded. - Alias expansion is done on the shell input before any other expansion except history expansion. Therefore, if an alias is defined for the word tt(foo), alias expansion may be avoided by quoting part of the @@ -586,11 +577,40 @@ tt(\foo) as well. Also, if a separator such as tt(&&) is aliased, tt(\&&) turns into the two tokens tt(\&) and tt(&), each of which may have been aliased separately. Similarly for tt(\<<), tt(\>|), etc. +When tt(POSIX_ALIASES) is set, only plain unquoted strings are eligible +for aliasing. The tt(alias) builtin does not reject ineligible aliases, +but they are not expanded. + For use with completion, which would remove an initial backslash followed by a character that isn't special, it may be more convenient to quote the word by starting with a single quote, i.e. tt('foo); completion will automatically add the trailing single quote. +subsect(Alias difficulties) + +Although aliases can be used in ways that bend normal shell syntax, not +every string of non-white-space characters can be used as an alias. + +Any set of characters not listed as a word above is not a word, hence no +attempt is made to expand it as an alias, no matter how it is defined +(i.e. via the builtin or the special parameter tt(aliases) described in +ifnzman(noderef(The zsh/parameter Module))\ +ifzman(the section THE ZSH/PARAMETER MODULE in zmanref(zshmodules))). +However, as noted in the case of tt(POSIX_ALIASES) above, the shell does +not attempt to deduce whether the string corresponds to a word at the +time the alias is created. + +For example, an expression containing an tt(=) at the start of +a command line is an assignment and cannot be expanded as an alias; +a lone tt(=) is not an assignment but can only be set as an alias +using the parameter, as otherwise the tt(=) is taken part of the +syntax of the builtin command. + +It is not presently possible to alias the `tt(LPAR()LPAR())' token that +introduces arithmetic expressions, because until a full statement has been +parsed, it cannot be distinguished from two consecutive `tt(LPAR())' +tokens introducing nested subshells. + There is a commonly encountered problem with aliases illustrated by the following code: -- cgit 1.4.1