保存环境变量而不使用/ bin / bash

Question

I have a program that creates a environment variable called $EGG with this code

 memcpy(buff,"EGG=",4);
 putenv(buff); 
 system("/bin/bash"); 

And the value of buff is used to create an environment variable, and I use it through $EGG variable, but for use it I see that I must use the call system("/bin/bash"); . Otherwise, if I don't use /bin/bash call I don't find my $EGG variable.

Is there a way to save my environment variable without calling /bin/bash ?

Answer 1

Short answer: You cannot modify an existing environment the way you try.

Background: The program you use to create the environment variable EGG in gets its own environment on start-up (typically as copy of the environment of the process that starts the program). Inside the program's very own environment EGG is created.

When a program ends its environment is also gone and with it would had been created in there.

To modify an environment programmatically do not write a (C) program but use a script.

Using bash this could look like this:

#!/bin/bash
export EGG=4

save this as for example set_egg_to_4.sh and adjust the files mode do be able to execute the it:

$ chmod +x set_egg_to_4.sh

Then run the script:

$ ./set_egg_to_4.sh

and test for EGG , by doing

$ echo $EGG
4

Answer 2

To "permanently" set an environment variable, add it to your .bash_profile file.

export EGG=4

This file is sourced each time you start a login session, so that EGG is added to your environment each time. Any that inherit (directly or indirectly) from this shell will also have EGG in its environment.

There may be other files on your system that are sourced immediately on startup, so that a variable set in such a file is available to all processes (regardless of the user). (One I'm think of is /etc/environment .)