“e” suffix

The “e” suffix versions pass an environment to the program. An environment is just that—a kind of “context” for the program to operate in. For example, you may have a spelling checker that has a dictionary of words. Instead of specifying the dictionary's location every time on the command line, you could provide it in the environment:

$ export DICTIONARY=/home/rk/.dict

$ spellcheck document.1

The export command tells the shell to create a new environment variable (in this case, DICTIONARY), and assign it a value (/home/rk/.dict).

If you ever wanted to use a different dictionary, you'd have to alter the environment before running the program. This is easy from the shell:

$ export DICTIONARY=/home/rk/.altdict

$ spellcheck document.1

But how can you do this from your own programs? To use the e versions of spawn() and exec(), you specify an array of strings representing the environment:

char *env [] =

// To start the spell-checker:
spawnle (P_WAIT, "/usr/bin/spellcheck", "/usr/bin/spellcheck",
         "document.1", NULL, env);

// To transform into the spell-checker:
execle ("/usr/bin/spellcheck", "/usr/bin/spellcheck",
        "document.1", NULL, env);