'--file <filename>' can be used to tell the command to write to
that location (you can say '--local' but that is the default).
-This command will fail (with exit code ret) if:
+This command will fail with non-zero status upon error. Some exit
+codes are:
. The config file is invalid (ret=3),
. can not write to the config file (ret=4),
. no section or name was provided (ret=2),
. the section or key is invalid (ret=1),
. you try to unset an option which does not exist (ret=5),
-. you try to unset/set an option for which multiple lines match (ret=5),
-. you try to use an invalid regexp (ret=6), or
-. you use '--global' option without $HOME being properly set (ret=128).
+. you try to unset/set an option for which multiple lines match (ret=5), or
+. you try to use an invalid regexp (ret=6).
On success, the command returns the exit code 0.