diff --git a/runatlantis.io/docs/custom-workflows.md b/runatlantis.io/docs/custom-workflows.md
index 4a485be341..89d3f9eb0e 100644
--- a/runatlantis.io/docs/custom-workflows.md
+++ b/runatlantis.io/docs/custom-workflows.md
@@ -349,6 +349,7 @@ Or a custom command
   * `PROJECT_NAME` - Name of the project configured in `atlantis.yaml`. If no project name is configured this will be an empty string.
   * `PULL_NUM` - Pull request number or ID, ex. `2`.
   * `PULL_AUTHOR` - Username of the pull request author, ex. `acme-user`.
+  * `REPO_REL_DIR` - The relative path of the project in the repository. For example if your project is in `dir1/dir2/` then this will be set to `"dir1/dir2"`. If your project is at the root this will be `"."`.
   * `USER_NAME` - Username of the VCS user running command, ex. `acme-user`. During an autoplan, the user will be the Atlantis API user, ex. `atlantis`.
   * `COMMENT_ARGS` - Any additional flags passed in the comment on the pull request. Flags are separated by commas and
   every character is escaped, ex. `atlantis plan -- arg1 arg2` will result in `COMMENT_ARGS=\a\r\g\1,\a\r\g\2`.
diff --git a/server/events/runtime/run_step_runner.go b/server/events/runtime/run_step_runner.go
index 3cec95bb87..e4d0015b93 100644
--- a/server/events/runtime/run_step_runner.go
+++ b/server/events/runtime/run_step_runner.go
@@ -51,6 +51,7 @@ func (r *RunStepRunner) Run(ctx models.ProjectCommandContext, command string, pa
 		"PROJECT_NAME":               ctx.ProjectName,
 		"PULL_AUTHOR":                ctx.Pull.Author,
 		"PULL_NUM":                   fmt.Sprintf("%d", ctx.Pull.Num),
+		"REPO_REL_DIR":               ctx.RepoRelDir,
 		"USER_NAME":                  ctx.User.Username,
 		"WORKSPACE":                  ctx.Workspace,
 	}
diff --git a/server/events/runtime/run_step_runner_test.go b/server/events/runtime/run_step_runner_test.go
index 7f739e48e2..f662fbf1cd 100644
--- a/server/events/runtime/run_step_runner_test.go
+++ b/server/events/runtime/run_step_runner_test.go
@@ -65,8 +65,8 @@ func TestRunStepRunner_Run(t *testing.T) {
 			ExpOut:      "workspace=myworkspace version=0.11.0 dir=$DIR planfile=$DIR/my::project::name-myworkspace.tfplan project=my/project/name\n",
 		},
 		{
-			Command: "echo base_repo_name=$BASE_REPO_NAME base_repo_owner=$BASE_REPO_OWNER head_repo_name=$HEAD_REPO_NAME head_repo_owner=$HEAD_REPO_OWNER head_branch_name=$HEAD_BRANCH_NAME base_branch_name=$BASE_BRANCH_NAME pull_num=$PULL_NUM pull_author=$PULL_AUTHOR",
-			ExpOut:  "base_repo_name=basename base_repo_owner=baseowner head_repo_name=headname head_repo_owner=headowner head_branch_name=add-feat base_branch_name=master pull_num=2 pull_author=acme\n",
+			Command: "echo base_repo_name=$BASE_REPO_NAME base_repo_owner=$BASE_REPO_OWNER head_repo_name=$HEAD_REPO_NAME head_repo_owner=$HEAD_REPO_OWNER head_branch_name=$HEAD_BRANCH_NAME base_branch_name=$BASE_BRANCH_NAME pull_num=$PULL_NUM pull_author=$PULL_AUTHOR repo_rel_dir=$REPO_REL_DIR",
+			ExpOut:  "base_repo_name=basename base_repo_owner=baseowner head_repo_name=headname head_repo_owner=headowner head_branch_name=add-feat base_branch_name=master pull_num=2 pull_author=acme repo_rel_dir=mydir\n",
 		},
 		{
 			Command: "echo user_name=$USER_NAME",