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To: cygwin AT cygwin DOT com References: <838469265 DOT 20160401235308 AT yandex DOT ru> <87a8lcicxg DOT fsf AT Rainer DOT invalid> <5700975A DOT 3070002 AT cygwin DOT com> <87y48vqkfx DOT fsf AT Rainer DOT invalid> From: Dirk Fassbender Message-ID: <570102D3.6000502@arcor.de> Date: Sun, 3 Apr 2016 13:47:31 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.7.1 MIME-Version: 1.0 In-Reply-To: <87y48vqkfx.fsf@Rainer.invalid> Content-Type: text/plain; charset=iso-8859-15; format=flowed Content-Transfer-Encoding: 7bit Am 03.04.2016 um 08:24 schrieb Achim Gratz: > Yaakov Selkowitz writes: >> I am not in favour of /bin/sh being alternatives-able. > I'd posit that it should not be bash then and somwone else might > reasonably want a different /bin/sh, perhaps even bash. Which is > exactly why the alternatives system exists. > >> The *proper* course of action is to use the shebang for the script >> interpreter you require, i.e. /bin/dash. > It's perfectly OK to use /bin/sh (I'd even recommend it) if all you want > is a POSIX shell. You shouldn't be trying to use local then, but that's > another story (*). > > (*) http://stackoverflow.com/questions/18597697/posix-compliant-way-to-scope-variables-to-a-function-in-a-shell-script > > > Regards, > Achim. Hello, please have in mind that the /bin/sh shell is the system default shell. On Unix systems many initialisation scripts are executed during start up with the /bin/sh in a way that a shebang line is not used. So these scripts are executed with the standard /bin/sh every time. Because AIX and HP-UX are using a KSH (version 88), SOLARIS is using a Bourne shell version and Linux systems can use different shell types ( mostly DASH, BASH to my knowledge) it is difficult to write scripts to use during system initialization in a portable way. This comes from the way how the different shells behave then invoked as /bin/sh. See the following section from the bash man page. If*bash*is invoked with the name*sh*, it tries to mimic the startup behavior of historical versions of*sh*as closely as possible, while conforming to the POSIX standard as well. When invoked as an interactive login shell, or a non-interactive shell with the*--login*option, it first attempts to read and execute commands from//etc/profile/ and/~/.profile/ , in that order. The*--noprofile*option may be used to inhibit this behavior. When invoked as an interactive shell with the name*sh*,*bash*looks for the variable*ENV*,expands its value if it is defined, and uses the expanded value as the name of a file to read and execute. Since a shell invoked as*sh*does not attempt to read and execute commands from any other startup files, the*--rcfile*option has no effect. A non-interactive shell invoked with the name*sh*does not attempt to read any other startup files. When invoked as*sh*,*bash*enters/posix/mode after the startup files are read. KSH behave in a similar way. So it is not easy to write portable scripts for the standard shell /bin/sh between different systems and the exchange of the standard shell needs a check for all scripts, that uses a shebang line /bin/sh or are use during system initialisation. I personally prefer to use a shebang line set to the shell type used (ksh, bash, dash). This is more portable for different system types. For putting the /bin/sh under alternatives control on cygwin there must be some preparations. There are several postinstall and preremove scripts without a shebang line or with a shebang line /bin/sh or /usr/bin/sh. Are all of these scripts written to run correctly with a bash and dash invoked ? Regards Dirk Fassbender -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple