tcl file is unable to get environment variable which is set through code

Question

I have set the environment variable through my code using putenv. I am reading the environment variable through tcl file. It seems , in windows this is showing the following Error : can't read "env(myvar)": no such variable, no such variable (read trace on "env(myvar)") invoked from within "puts $env(myar)"

but in Linux the error is not coming.

putenv is used to set environment variable $env() is used in tcl file to get env.

"not working" is not a useful problem description. – Robert Columbia Mar 25 '19 at 16:38 — Robert Columbia, Mar 25 '19 at 16:38
Problem has been edited, Thanks – vishu Mar 26 '19 at 05:27 — vishu, Mar 26 '19 at 05:27

score 1 · Answer 1 · answered Mar 25 '19 at 14:13

This is known, and is caused by the fact that if we synchronize more exactly there's a much larger performance penalty for all accesses to environment variables from Tcl, and that's a much more common use case than the one you have where you are changing the environment variable from C code. (The putenv() system call doesn't give us anything we can efficiently hook to detect the changes, so we end up having to reassemble the whole env array from scratch; this was found to be a significant bottleneck.)

The simplest workaround is for you to create a little extra command in Tcl (but written in C) that wraps the getenv() call directly so that you can use that with environment variables that you suspect may have been changed behind Tcl's back.

int WrapGetEnv(ClientData ignored, Tcl_Interp *interp, int argc, char *argv[]) {
    if (argc != 2) {
        // Probably ought to be a better error here
        return TCL_ERROR;
    }
    char *var = argv[1];
    char *val = getenv(var);
    if (val != NULL) {
        Tcl_SetResult(interp, val, TCL_DYNAMIC);
    }
    return TCL_OK;
}

// ... in the right place do this ...
Tcl_CreateCommand(interp, "getenv", WrapGetEnv, NULL, NULL);

But this issue seems to come in windows as well as Linux. But in my case, issue is only coming with windows. Is there any reason for the same ? — vishu, Mar 26 '19 at 10:29

tcl file is unable to get environment variable which is set through code

1 Answers1