Add run-if-checksum-changed-script

README.md

@@ -212,12 +212,15 @@ commands:
 ```
 
 ##### `cmd`
+
 `key: cmd`
 
 `type: string or array of strings`
 
 Actual command to run in shell.
 
+You can access command name in your script, it stored in env var `LETS_CMD`
+
 Can be either a string (also a multiline string) or an array of strings.
 
 The main difference is that when specifying an array, all args, specified in terminal will be appended to cmd array 
@@ -485,3 +488,21 @@ You can use Bash/Zsh/Oh-My-Zsh completion in you terminal
 * **Zsh/Oh-My-Zsh**
 
     There is a [repo](https://github.com/lets-cli/lets-zsh-plugin) with zsh plugin with instructions
+
+### Useful scrips
+
+You can use this bash scripts in your own `lets.yaml` in case, if you wish to implement some functionality, that does not implemented yet in Lets
+
+- run cmd only if checksum was changed
+    > Do't forget to add `.lets/` into your `.gitignore `
+    ```yaml
+    # lets.yaml
+    commands:
+      build:
+        cmd: scripts/run-if-checksum-changed.sh "docker build ."
+      #           |-------path to bash script------|---cmd to run---|
+      run:
+        depends:
+          - build
+        cmd: docker-compose up
+    ```

commands/run.go

@@ -2,14 +2,15 @@ package commands
 
 import (
 	"fmt"
-	"github.com/docopt/docopt-go"
-	"github.com/lets-cli/lets/commands/command"
-	"github.com/lets-cli/lets/config"
-	"github.com/lets-cli/lets/logging"
 	"io"
 	"os"
 	"os/exec"
 	"strings"
+
+	"github.com/docopt/docopt-go"
+	"github.com/lets-cli/lets/commands/command"
+	"github.com/lets-cli/lets/config"
+	"github.com/lets-cli/lets/logging"
 )
 
 const (
@@ -112,6 +113,7 @@ func runCmd(cmdToRun command.Command, cfg *config.Config, out io.Writer, parentN
 		convertEnvMapToList(cmdToRun.CliOptions),
 		convertChecksumToEnvForCmd(cmdToRun.Checksum),
 		convertChecksumMapToEnvForCmd(cmdToRun.ChecksumMap),
+		[]string{makeEnvEntry("LETS_CMD", cmdToRun.Name)},
 	)
 	if !isChildCmd {
 		logging.Log.Debugf(

useful-scripts/run-if-checksum-changed.sh

@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+
+CMD=$1
+NEW_CHECKSUM=$LETS_CHECKSUM
+LABEL=$LETS_CMD
+LETS_DIR=.lets
+
+# ensure lets dir exists
+if [[ ! -d "$LETS_DIR" ]]; then
+    mkdir $LETS_DIR
+fi;
+# ensure checksum file exists
+if [[ ! -f "$LETS_DIR/$LABEL" ]]; then
+    touch $LETS_DIR/$LABEL
+fi;
+
+# read
+PREV_CHECKSUM=$(head -n 1 $LETS_DIR/$LABEL)
+
+if [[ "$NEW_CHECKSUM" != "$PREV_CHECKSUM" ]]; then
+    # update checksum
+    echo $NEW_CHECKSUM > $LETS_DIR/$LABEL
+    eval $CMD
+fi;