[bug-gawk] Inconsistent External Command Spawning

[David Millis]

The ways gawk executes System() and piped commands is inconsistent again.
system() and pipe execution need to spawn the same way.

The subject of WHICH way has returned.

Previously discussed here.
http://lists.gnu.org/archive/html/bug-gawk/2012-04/msg00003.html


Using Klabaster's binaries, which I think are built from canonical source.
4.1.0: Pipe:Quotes, System:Bat

4.0.1: Pipe:Bat, System:Bat

4.0.0: Pipe:Bat, System:Quotes

And, for completeness, GnuWin32's noncanonical build
3.1.6: Pipe:Quotes, System:Quotes

Quotes = cmd.exe /C blah
Requires a script author to concatenate fodder quotes around the external 
command - because CMD predictably eats the first and last - but otherwise 
executes exactly* as if the command were written in a shell prompt.

Bat = blah is written to a temporary batch file, then that is executed.
The external command will be subject to CMD's special batch parsing rules 
regarding percents, among other things.

* In this post, I outlined in detail what I understood to be how the windows 
runtime and cmd.exe interact to ultimately run the external command... the way 
other languages do it.
http://lists.gnu.org/archive/html/bug-gawk/2012-04/msg00018.html


In the previous thread, Eli Zaretskii's responses started and concluded...

"The GnuWin32 way was simply unworkable, because
(a) there are differences in handling quoted arguments between the Windows 
runtime libraries supplied with Windows Vista and later, and the runtime in 
older Windows versions, like XP; and
(b) there are certain situations where you simply _cannot_ get the desired 
effect by _any_ reasonable use of quotes, due to misfeatures of how quotes are 
handled by the Windows APIs and the startup code of programs you invoke via the 
'system' function."

"When I have time, or if I bump into that by chance, I will show you examples 
of trouble with quoting+cmd+other apps."


I'm still not aware of any example showing the inadequacy of ALWAYS using this 
in a script
system("\"+ any_command_line_regardless_of_quotes_or_wildcards +"\"")
on builds where
system(sysarg)
is
cmd.exe /C sysarg

The alleged inadequacy of fodder quotes was the whole argument for resorting to 
temporary batch files.
Conversely,
system( gensub(/%/, "%%", any_command_line_regardless_of_quotes_or_wildcards) ) 

was deemed good enough for MOST cases when run as a batch.

So long as the spawn methods keep changing, it's difficult to write scripts 
using external commands that reliably work across builds (a script that manages 
this was attached in the link at the top).


David