Re: ksh compatibility: initial value of $_

[Jun T <takimoto-j@kba.biglobe.ne.jp>]

> 2023/01/28 10:52, Bart Schaefer <schaefer@brasslantern.com> wrote:
> 
> Docs for ksh93 say that $_ should be initialized to the absolute path
> of what we put in $ZSH_ARGZERO.
> 
> Src/init.c explicitly initializes $_ to the empty string.
> 
> Any reason not to change this?

No reason, I think, but I don't know any portable way to obtain
the full path name of the current zsh executable.

>  If so, where's the right place to do
> it?  I tried doing it in createparamtab() but that led to memory
> errors.

Once the full path name is obtained, then I guess we can initialize
$_ in setupvals() as in the following pseudo-patch:

diff --git a/Src/init.c b/Src/init.c
index 68621a0ad..03cbe4d0e 100644
--- a/Src/init.c
+++ b/Src/init.c
@@ -1084,9 +1084,12 @@ setupvals(char *cmd, char *runscript, char *zsh_name)
 	ztrdup(DEFAULT_IFS_SH) : ztrdup(DEFAULT_IFS);
     wordchars   = ztrdup(DEFAULT_WORDCHARS);
     postedit    = ztrdup("");
-    zunderscore  = (char *) zalloc(underscorelen = 32);
-    underscoreused = 1;
-    *zunderscore = '\0';
+    /* assume full path name of this zsh is in 'mypath' */
+    underscoreused = strlen(mypath) + 1;
+    underscorelen = (underscoreused + 31) & ~31;
+    zunderscore = (char *) zalloc(underscorelen);
+    strcpy(zunderscore, mypath);
+    /* free 'mypath' if necessary */
 
     zoptarg = ztrdup("");
     zoptind = 1;