On Fri, Jun 5, 2009 at 10:50 AM, L.Tomei<[email protected]> wrote:
> Is there an easy way in J to recognize Unix symbolic links?
Just use the dynamic call interface (15!:0). As the function you want
to call, lstat, is in libc, there'd probably be all kinds of
complications from calling it directly, so the easiest way is to just
write a wrapper. Here's an example of what works on my system.
[am]king ~/a/tmp$ cat wrap_lstat.c
#include <stdio.h>
#include <sys/stat.h>
#include <unistd.h>
int
wrap_lstat_type(const char *fname) {
struct stat b;
int r;
r = lstat(fname, &b);
return r ? -1 : b.st_mode;
}
[am]king ~/a/tmp$ gcc -Wall -O -fPIC -shared -o wrap_lstat.so wrap_lstat.c
[am]king ~/a/tmp$ jconsole
,.l=: '/usr/' ,&.:>"_ 0 {."1] 1!:0 <'/usr/*'
+------------+
|/usr/bin |
+------------+
|/usr/lib |
+------------+
|/usr/src |
+------------+
|/usr/sbin |
+------------+
|/usr/X11R6 |
+------------+
|/usr/games |
+------------+
|/usr/lib32 |
+------------+
|/usr/lib64 |
+------------+
|/usr/local |
+------------+
|/usr/share |
+------------+
|/usr/include|
+------------+
lstat_type=: './wrap_lstat.so wrap_lstat_type > i *c' (15!:0) ,@:<@:>
islink =: 8b120000 = 8b170000 (17 b.) lstat_type
(<@:islink,])"0 l
+-+------------+
|0|/usr/bin |
+-+------------+
|0|/usr/lib |
+-+------------+
|0|/usr/src |
+-+------------+
|0|/usr/sbin |
+-+------------+
|0|/usr/X11R6 |
+-+------------+
|0|/usr/games |
+-+------------+
|1|/usr/lib32 |
+-+------------+
|1|/usr/lib64 |
+-+------------+
|0|/usr/local |
+-+------------+
|0|/usr/share |
+-+------------+
|0|/usr/include|
+-+------------+
[am]king ~/a/tmp$ l /usr
./ X11R6/ games/ lib/ lib64@ sbin/ src/
../ bin/ include/ lib32@ local/ share/
[am]king ~/a/tmp$
The output of ls shows that lib32 and lib64 are symlinks on my system,
and the islink function in J gives the same result. (I was lazy and
just hardcoded the usual values of the constants S_IFMT and S_IFLNK,
but you could export these from the C wrapper as well if you wanted to
go for sure.)
(This is on an amd64 linux system.)
Ambrus
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