On Wed, 4 Apr 2012, Honza wrote:
2012/4/4 <[email protected]>:
Not the current.
The EXTERNAL variable environ, i.e. the one that the kernel passed on,
which cannot be modified. You can only modify your local copy.
14:00 myname@tux64:~/tmp/c$ ls
a.c b.c
14:00 myname@tux64:~/tmp/c$ cat a.c
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
main() {
char *e = getenv("MYVAR");
printf("a1: %s\n", e);
setenv("MYVAR", "MYVALUE", 1);
e = getenv("MYVAR");
printf("a2: %s\n", e);
execv("./b.out", NULL);
}
14:00 myname@tux64:~/tmp/c$ cat b.c
#include <stdlib.h>
#include <stdio.h>
main() {
char *e = getenv("MYVAR");
printf("b: %s\n", e);
}
14:00 myname@tux64:~/tmp/c$ gcc -o a.out a.c && gcc -o b.out b.c && ls
a.c a.out b.c b.out
14:00 myname@tux64:~/tmp/c$ ./a.out
a1: (null)
a2: MYVALUE
b: MYVALUE
14:00 myname@tux64:~/tmp/c$
Output of strace:
brk(0) = 0x21a5000
brk(0x21c6000) = 0x21c6000
write(1, "a2: MYVALUE\n", 12a2: MYVALUE
) = 12
execve("./b.out", [0], [/* 57 vars */]) = 0
brk(0) = 0x189e000
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or
directory)
As you can see, it uses execve() behind the scenes to be able to pass the
modified
local environment.
This is libc-specific behaviour.
Michael.
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