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Commit 503a0b8 from git://git.kernel.org/pub/scm/utils/dash/dash.git by Herbert Xu says: >The parsebackquote flag is only used in a test where it always has the >value zero. So we can remove it altogether. The first statement is incorrect: parsebackquote is non-zero when backquotes (as opposed to $(...)) are used for command substitution. It is possible for the test to be executed with parsebackquote != 0 in that case. The test is question checks whether quotes have been closed, raising the error "unterminated quoted string" if they haven't. There seems to be no good reason to allow unclosed quotes within backquotes. Bash, hush and dash (after commit 503a0b8) all treat the following as an error: XX=`"pwd` whereas BusyBox ash doesn't. It just ignores the unclosed quote and executes pwd. So, parsebackquote should be removed but not for the reason stated. function old new delta parsebackquote 1 - -1 readtoken1 3222 3182 -40 ------------------------------------------------------------------------------ (add/remove: 0/1 grow/shrink: 0/1 up/down: 0/-41) Total: -41 bytes Signed-off-by: Ron Yorston <rmy@frippery.org> Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
http://www.opengroup.org/onlinepubs/9699919799/ Open Group Base Specifications Issue 7 http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap01.html Shell & Utilities It says that any of the standard utilities may be implemented as a regular shell built-in. It gives a list of utilities which are usually implemented that way (and some of them can only be implemented as built-ins, like "alias"): alias bg cd command false fc fg getopts jobs kill newgrp pwd read true umask unalias wait http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html Shell Command Language It says that shell must implement special built-ins. Special built-ins differ from regular ones by the fact that variable assignments done on special builtin are *PRESERVED*. That is, VAR=VAL special_builtin; echo $VAR should print VAL. (Another distinction is that an error in special built-in should abort the shell, but this is not such a critical difference, and moreover, at least bash's "set" does not follow this rule, which is even codified in autoconf configure logic now...) List of special builtins: . file : [argument...] break [n] continue [n] eval [argument...] exec [command [argument...]] exit [n] export name[=word]... export -p readonly name[=word]... readonly -p return [n] set [-abCefhmnuvx] [-o option] [argument...] set [+abCefhmnuvx] [+o option] [argument...] set -- [argument...] set -o set +o shift [n] times trap n [condition...] trap [action condition...] unset [-fv] name... In practice, no one uses this obscure feature - none of these builtins gives any special reasons to play such dirty tricks. However. This section also says that *function invocation* should act similar to special built-in. That is, variable assignments done on function invocation should be preserved after function invocation. This is significant: it is not unthinkable to want to run a function with some variables set to special values. But because of the above, it does not work: variable will "leak" out of the function.