diff --git a/README.md b/README.md
index 3908e90..b228941 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # git-trigger
 
-git-trigger monitors a git branch and trigger a command defined in config file when changes are detected.
+git-trigger monitors a git branch and trigger a shell command defined in config file when changes are detected.
 
 ## Usage
 
@@ -53,6 +53,31 @@ module.exports = {
 }
 ```
 
+## Configuration parameters
+
+- interval: number
+  - intervals milliseconds for check git branches
+- repositories: Array
+   - url: string
+      - target git repository
+   - branch: string
+      - target branch name
+   - dir: string
+      - clone directory
+   - actions: Array
+      - when: "changed"|"always"
+      - gitCmd: string(optional)
+         - git sub command executed before `run` command
+      - run: string(optional)
+         - shell command
+
+## Environment variables in command
+
+git-trigger assigns the following environtment variables to a command in `run` parameter.
+
+- `GIT_TRIGGER_COMMIT_HASH`
+- `GIT_TRIGGER_PREV_COMMIT_HASH`
+
 ## Live config update
 
 `git-trigger` supports live config update by `SIGUSR1` signal.
diff --git a/src/Config.ts b/src/Config.ts
index 5e523a3..d731ef7 100644
--- a/src/Config.ts
+++ b/src/Config.ts
@@ -1,6 +1,6 @@
 export interface ActionConfig {
-    gitCmd: string;
     when: "changed"|"always";
+    gitCmd?: string;
     run?: string;
 }
 
diff --git a/src/Runner.ts b/src/Runner.ts
index 41b8085..3666c72 100644
--- a/src/Runner.ts
+++ b/src/Runner.ts
@@ -1,5 +1,5 @@
 import Timer from "./Timer";
-import { Config, RepositoryConfig } from "./Config";
+import { Config } from "./Config";
 import * as fs from "fs-extra";
 import * as git from "./git";
 import * as execa from "execa";
@@ -48,14 +48,20 @@ export default class Runner {
                     console.error("error: " + repo.dir + " is not " + repo.branch + " branch");
                     continue;
                 }
-                const changed = await git.remoteChanged(repo.branch, repo.dir);
+                const [changed, prevHash] = await git.remoteChanged(repo.branch, repo.dir);
                 for (const act of repo.actions) {
                     if (act.when === "changed" && !changed) {
                         continue;
                     }
-                    await git.exec(act.gitCmd, repo.dir);
+                    if (act.gitCmd) {
+                        await git.exec(act.gitCmd, repo.dir);
+                    }
                     if (act.run) {
-                        await execa.shell(act.run, {cwd: repo.dir});
+                        const commitHash = await git.commitHash(repo.dir);
+                        await execa.shell(act.run, {cwd: repo.dir, env: {
+                            GIT_TRIGGER_COMMIT_HASH: commitHash,
+                            GIT_TRIGGER_PREV_COMMIT_HASH: prevHash
+                        }});
                     }
                 }
                 console.log("success: " + JSON.stringify({url: repo.url, branch: repo.branch, dir: repo.dir}));
diff --git a/src/git.ts b/src/git.ts
index ea9028c..336d990 100644
--- a/src/git.ts
+++ b/src/git.ts
@@ -14,12 +14,20 @@ export async function remoteUrl(cwd: string): Promise<string> {
     return url;
 }
 
-export async function remoteChanged(branch: string, cwd: string): Promise<boolean> {
-    const {stdout: remote} = await execa("git", ["ls-remote", "origin", "refs/heads/" + branch], {cwd});
-    const {stdout: local} = await execa("git", ["rev-parse", "HEAD"], {cwd});
-    return remote.indexOf(local) !== 0;
+export async function remoteChanged(branch: string, cwd: string): Promise<[boolean, string, string]> {
+    const remote = await (async () => {
+        const {stdout} = await execa("git", ["ls-remote", "origin", "refs/heads/" + branch], {cwd});
+        return stdout.split("\t")[0].split(" ")[0];
+    })();
+    const local = await commitHash(cwd);
+    return [remote !== local, local, remote];
 }
 
 export async function exec(cmd: string, cwd: string): Promise<void> {
     await execa("git", cmd.split(" "), {cwd});
 }
+
+export async function commitHash(cwd: string): Promise<string> {
+    const { stdout } = await execa("git", ["rev-parse", "HEAD"], {cwd});
+    return stdout;
+}