Re: ksh (IEEE Std 1003.1-2008 ?)
On Fri, Jan 8, 2010 at 10:18 PM, J.C. Roberts list-...@designtools.org wrote: I've been looking for standards on correct variable scope in ksh but the IEEE Std 1003.1-2008 stuff on the Open Group site doesn't mention any rules? http://www.opengroup.org/onlinepubs/9699919799/utilities/contents.html The key section is 2.12: http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_12 To selectively quote: A shell execution environment consists of the following: ... * Shell parameters that are set by variable assignment (see the set special built-in) or from the System Interfaces volume of POSIX.1-2008 environment inherited by the shell when it begins (see the export special built-in) ... A subshell environment shall be created as a duplicate of the shell environment, except that signal traps set by that shell environment shall be set to the default values. Changes made to the subshell environment shall not affect the shell environment. ... Additionally, each command of a multi-command pipeline is in a subshell environment; as an extension, however, any or all commands in a pipeline may be executed in the current environment. All other commands shall be executed in the current shell environment. I found an interesting behavior in our ksh (pdksh) implementation, and I'd like to know if the behavior is considered correct? Yes, it is. When you append to a variable within a 'for' loop, the changes are exist after the loop ends, but if you do the same within a 'while' loop, the changes are lost? It has nothing to do with 'for' vs 'while' and everything to do with your using 'for' as a single-command and 'while' in a multi-command pipeline. If you prefix the 'for' command with echo foo | then you'll see the same behavior with it. I realize the IEEE/POSIX standard was based on ksh93, and our pdksh is only partially compliant with ksh93, but I'm wondering if the correct behavior for variable scope is formally standardized and/or documented anywhere? See above. Philip Guenther
Re: ksh (IEEE Std 1003.1-2008 ?)
On Sat, 9 Jan 2010 08:51:31 +0100 Matthias Kilian k...@outback.escape.de wrote: n Fri, Jan 08, 2010 at 10:18:39PM -0800, J.C. Roberts wrote: When you append to a variable within a 'for' loop, the changes are exist after the loop ends, but if you do the same within a 'while' loop, the changes are lost? [...] # Now we try the same type of thing with the 'while' loop. cat list.txt | while read -r WNAME; do [...] That while loop is running in a separate process; the parent process won't see any variable changes made in the loop. Ciao, Kili Bah! I totally missed that. Makes sense now. Thanks Kili. If I use redirection rather than piping for input to the `while` loop, it is not a separate process, and works like the 'for' loop. while read -r WNAME; do if [[ -z $WLIST ]]; then WLIST=$WNAME; else WLIST=$WLIST $WNAME; fi printf WLIST: %s\n $WLIST; done list.txt If I wanted to use the other method with cat list.txt |, I'd have to use a co-process | to talk to the 'while' loop (and read -p/print -p) and get the changes to the variables. -- J.C. Roberts
Re: ksh (IEEE Std 1003.1-2008 ?)
On Sat, Jan 09, 2010 at 12:43:05AM -0800, J.C. Roberts wrote: If I use redirection rather than piping for input to the `while` loop, it is not a separate process, and works like the 'for' loop. I have seen some Unix systems where this doesn't work, either. See http://groups.google.com/group/comp.unix.programmer/browse_thread/thread/20872c6fe79dd153/f3a4f184d0c6a718
Re: ksh (IEEE Std 1003.1-2008 ?)
On Sat, 9 Jan 2010 14:56:02 + Matthew Szudzik mszud...@andrew.cmu.edu wrote: On Sat, Jan 09, 2010 at 12:43:05AM -0800, J.C. Roberts wrote: If I use redirection rather than piping for input to the `while` loop, it is not a separate process, and works like the 'for' loop. I have seen some Unix systems where this doesn't work, either. See http://groups.google.com/group/comp.unix.programmer/browse_thread/thread/20872c6fe79dd153/f3a4f184d0c6a718 Reminds me of this: It is easier to port a shell than a shell script. -- Larry Wall :-) -- J.C. Roberts
Re: ksh (IEEE Std 1003.1-2008 ?)
On Fri, Jan 08, 2010 at 10:18:39PM -0800, J.C. Roberts wrote: When you append to a variable within a 'for' loop, the changes are exist after the loop ends, but if you do the same within a 'while' loop, the changes are lost? [...] # Now we try the same type of thing with the 'while' loop. cat list.txt | while read -r WNAME; do [...] That while loop is running in a separate process; the parent process won't see any variable changes made in the loop. Ciao, Kili
