Re: Caret escaping

[Alessandro Vesely]

Paul D. Smith wrote:
> %% Alessandro Vesely <address@hidden> writes:
>
>   av> Thus, in case the "slow path" is taken, the LINE command should be 
> replaced with
>   av> SHELL FLAG ESCAPED-LINE, where:
>   av>   SHELL may be either a unixy_shell, cmd.exe or the old command.com,
>   av>   FLAG should be -c for unixy_shell or /C otherwise, and
>   av>   ESCAPED-LINE should be escaped using backslashes for unixy_shell,
>   av>     carets for cmd.exe, or
>   av>     no escape at all for the old command.exe.
>   av> Then there is a batch_mode_shell flag, which is usually set for cmd.exe
>   av> and causes a NOT-SO-ESCAPED-LINE to be written to a temporary batch file.
>   av> Should we revise those specs in order to make a smarter use of cmd.exe?
>
>   av> Althought that patch also allowed -jN to be specified w/o
>   av> unixy_shell, after Paul's clarifications it seems the "-j"-change
>   av> does not depend on escaping.
>
>   av> Typically, smarter escaping might be required if the command is, say,
>
>   av>     egrep ^foo $^ | something
>
>   av> In that case, cmd.exe eats the caret unless it is escaped as ^^foo;
>   av> command.com does not. As a workaround one can escape the command in
>   av> the makefile, which then cannot be ported to windows 98.
>
> It may be that the DOS/Windows port does more with this than the UNIX
> port; I'm pretty sure there's no need to escape anything in UNIX since
> the string is passed directly to the shell with exec().

It looks as if the code in job.c is executed in normal Unix mode,
I mean w/o -j. I include a tentative call graph (the generated gif is in
http://www.tana.it/job_graph.gif for those who don't have dot at hands).

Escaping takes place while constructing command argv. It is a difficult piece
of code, because of recursion with many preprocessing #if's. It has been
modified recently to keep backslashes/newline according to POSIX. And it is
where patch #3678 was meant to be applied.

/*
 partial call graph of job.c functions
 (except execute_file_commands that lives in commands.c)
 usage: dot -Tgif -ojob_graph.gif job_graph.txt
*/

digraph G {
        execute_file_commands -> new_job;
        new_job -> start_waiting_jobs;
        new_job -> start_waiting_job;
        new_job -> reap_children;
        start_waiting_jobs -> start_waiting_job;
        start_waiting_jobs -> reap_children;
        start_waiting_job -> start_job_command;
        reap_children -> start_job_command;
        start_job_command -> start_job_command;
        start_job_command -> construct_command_argv;
        construct_command_argv -> construct_command_argv_internal;
        construct_command_argv_internal -> construct_command_argv_internal;
}