[RFA/RFC] Problem with '!' escaping with zsh/bash/ksh

[Joel Brobecker <brobecker@gnat.com>]

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Hello,

the following change introduced a problem when forking inferiors when
the path to the executable contains '!' characters. This only occurs
with sh-like shells, like zsh/bash/ksh. I have reproduced this on Linux
and HP/UX.

        * fork-inferior.c (fork_inferior): Add '!' to the list of
        characters that need to be quoted when building a string for the
        shell.  Quote '!' specifically with a backslash, since CSH chokes
        when trying to evaluate "str!str". 

Witness:

        (gdb) run
        Starting program: /home/brobecke/tmp/GEO_ENV!9.159/foo 
        zsh: no such file or directory: /home/brobecke/tmp/GEO_ENV\!9.159/foo
        
        Program exited with code 01.
        You can't do that without a process to debug.

As far as I can tell from the comments in fork_inferior and my own
experiments, the bang should be escaped only for C shells. To reflect
this, I have made the following change to fork-child.c.

2002-05-02  J. Brobecker  <brobecker@gnat.com>

        * fork-child.c (escape_bang_in_quoted_argument): New function.
        (fork_inferior): Escape '!' characters in quoted arguments
        only when needed.

Tested on HP/UX, with SHELL set to ZSH. No regression. Also tested by
verifying that it does fix the problem without breaking csh. Ok to apply?
Some better suggestions, maybe?

Thanks,
-- 
Joel

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Index: fork-child.c
===================================================================
RCS file: /nile.c/cvs/Dev/gdb/gdb-5.3/gdb/fork-child.c,v
retrieving revision 1.2
diff -c -3 -p -r1.2 fork-child.c
*** fork-child.c	16 Jan 2003 10:40:02 -0000	1.2
--- fork-child.c	2 May 2003 23:31:34 -0000
*************** breakup_args (char *scratch, char **argv
*** 93,98 ****
--- 93,121 ----
  
  }
  
+ /* When executing a command under the given shell, return non-zero
+    if the '!' character should be escaped when embedded in a quoted
+    command-line argument.  */
+ 
+ static int
+ escape_bang_in_quoted_argument (const char *shell_file)
+ {
+   const int shell_file_len = strlen (shell_file);
+   
+   /* Bang should be escaped only in C Shells.  For now, simply check
+      that the shell name ends with 'csh', which covers at least csh
+      and tcsh.  This should be good enough for now.  */
+ 
+   if (shell_file_len < 3)
+     return 0;
+ 
+   if (shell_file[shell_file_len - 3] == 'c'
+       && shell_file[shell_file_len - 2] == 's'
+       && shell_file[shell_file_len - 1] == 'h')
+     return 1;
+ 
+   return 0;
+ }
  
  /* Start an inferior Unix child process and sets inferior_ptid to its pid.
     EXEC_FILE is the file to run.
*************** fork_inferior (char *exec_file_arg, char
*** 176,181 ****
--- 199,205 ----
  
        char *p;
        int need_to_quote;
+       const int escape_bang = escape_bang_in_quoted_argument (shell_file);
  
        strcat (shell_command, "exec ");
  
*************** fork_inferior (char *exec_file_arg, char
*** 220,226 ****
  	    {
  	      if (*p == '\'')
  		strcat (shell_command, "'\\''");
! 	      else if (*p == '!')
  		strcat (shell_command, "\\!");
  	      else
  		strncat (shell_command, p, 1);
--- 244,250 ----
  	    {
  	      if (*p == '\'')
  		strcat (shell_command, "'\\''");
! 	      else if (*p == '!' && escape_bang)
  		strcat (shell_command, "\\!");
  	      else
  		strncat (shell_command, p, 1);