[PATCH] Allow environment variables to be unset in the processes started by run_command

[Alex Riesen <raa.lkml@gmail.com>]

To unset a variable, just specify its name, without "=". For example:

    const char *env[] = {"GIT_DIR=.git", "PWD", NULL};
    const char *argv[] = {"git-ls-files", "-s", NULL};
    int err = run_command_v_opt_cd_env(argv, RUN_GIT_CMD, ".", env);

The PWD will be unset before executing git-ls-files.

Signed-off-by: Alex Riesen <raa.lkml@gmail.com>
---

Alex Riesen, Wed, May 23, 2007 01:14:42 +0200:
> > Because you _scan_ the whole string in your patch to see if it
> > ends with = anyway, a trivial improvement would be to do:
> > 
> > 	if (strchr(cmd->env, '='))
> >                 putenv(cmd->env);
> > 	else
> >         	unsetenv(cmd->env);
> 
> I like this one. The env field in struct child_process and run_command
> will have to mention it in comments (in run-command.h), it's kind of
> special.
> 

 run-command.c |    8 ++++++--
 run-command.h |    5 +++++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/run-command.c b/run-command.c
index 605aa1e..3b1899e 100644
--- a/run-command.c
+++ b/run-command.c
@@ -77,8 +77,12 @@ int start_command(struct child_process *cmd)
 			die("exec %s: cd to %s failed (%s)", cmd->argv[0],
 			    cmd->dir, strerror(errno));
 		if (cmd->env) {
-			for (; *cmd->env; cmd->env++)
-				putenv((char*)*cmd->env);
+			for (; *cmd->env; cmd->env++) {
+				if (strchr(*cmd->env, '='))
+					putenv((char*)*cmd->env);
+				else
+					unsetenv(*cmd->env);
+			}
 		}
 		if (cmd->git_cmd) {
 			execv_git_cmd(cmd->argv);
diff --git a/run-command.h b/run-command.h
index af1e0bf..7958eb1 100644
--- a/run-command.h
+++ b/run-command.h
@@ -35,6 +35,11 @@ int run_command(struct child_process *);
 #define RUN_COMMAND_STDOUT_TO_STDERR 4
 int run_command_v_opt(const char **argv, int opt);
 int run_command_v_opt_cd(const char **argv, int opt, const char *dir);
+
+/*
+ * env (the environment) is to be formatted like environ: "VAR=VALUE".
+ * To unset an environment variable use just "VAR".
+ */
 int run_command_v_opt_cd_env(const char **argv, int opt, const char *dir, const char *const *env);
 
 #endif
-- 
1.5.2.67.gbd3c2