docs(if): add documentation for conditional execution

website/src/docs/guide.md

@@ -1007,6 +1007,99 @@ tasks:
       - echo "I will not run"
 ```
 
+### Conditional execution with `if`
+
+The `if` attribute allows you to conditionally skip tasks or commands based on a
+shell command's exit code. Unlike `preconditions` which fail and stop execution,
+`if` simply skips the task or command when the condition is not met and continues
+with the rest of the Taskfile.
+
+#### Task-level `if`
+
+When `if` is set on a task, the entire task is skipped if the condition fails:
+
+```yaml
+version: '3'
+
+tasks:
+  deploy:
+    if: '[ "$CI" = "true" ]'
+    cmds:
+      - echo "Deploying..."
+      - ./deploy.sh
+```
+
+#### Command-level `if`
+
+When `if` is set on a command, only that specific command is skipped:
+
+```yaml
+version: '3'
+
+tasks:
+  build:
+    cmds:
+      - cmd: echo "Building for production"
+        if: '[ "$ENV" = "production" ]'
+      - cmd: echo "Building for development"
+        if: '[ "$ENV" = "development" ]'
+      - go build ./...
+```
+
+#### Using templates in `if` conditions
+
+You can use Go template expressions in `if` conditions. Template expressions like
+`{{eq .VAR "value"}}` evaluate to `true` or `false`, which are valid shell
+commands (`true` exits with 0, `false` exits with 1):
+
+```yaml
+version: '3'
+
+tasks:
+  conditional:
+    vars:
+      ENABLE_FEATURE: "true"
+    cmds:
+      - cmd: echo "Feature is enabled"
+        if: '{{eq .ENABLE_FEATURE "true"}}'
+      - cmd: echo "Feature is disabled"
+        if: '{{ne .ENABLE_FEATURE "true"}}'
+```
+
+#### Using `if` with `for` loops
+
+When used inside a `for` loop, the `if` condition is evaluated for each iteration:
+
+```yaml
+version: '3'
+
+tasks:
+  process-items:
+    cmds:
+      - for: ['a', 'b', 'c']
+        cmd: echo "processing {{.ITEM}}"
+        if: '[ "{{.ITEM}}" != "b" ]'
+```
+
+This will output:
+
+```
+processing a
+processing c
+```
+
+#### `if` vs `preconditions`
+
+| Aspect | `if` | `preconditions` |
+|--------|------|-----------------|
+| On failure | Skips (continues) | Fails (stops) |
+| Message | Only in verbose mode | Always shown |
+| Use case | "Run if possible" | "Must be true" |
+
+Use `if` when you want optional conditional execution that shouldn't stop the
+workflow. Use `preconditions` when the condition must be met for the task to
+make sense.
+
 ### Limiting when tasks run
 
 If a task executed by multiple `cmds` or multiple `deps` you can control when it

website/src/docs/reference/schema.md

@@ -614,6 +614,27 @@ tasks:
       - ./deploy.sh
 ```
 
+#### `if`
+
+- **Type**: `string`
+- **Description**: Shell command to conditionally execute the task. If the
+  command exits with a non-zero code, the task is skipped (not failed).
+
+```yaml
+tasks:
+  # Task only runs in CI environment
+  deploy:
+    if: '[ "$CI" = "true" ]'
+    cmds:
+      - ./deploy.sh
+
+  # Using Go template expressions
+  build-prod:
+    if: '{{eq .ENV "production"}}'
+    cmds:
+      - go build -ldflags="-s -w" ./...
+```
+
 ### `dir`
 
 - **Type**: `string`
@@ -810,6 +831,27 @@ tasks:
           SERVICE: '{{.ITEM}}'
 ```
 
+### Conditional Commands
+
+Use `if` to conditionally execute a command. If the shell command exits with a
+non-zero code, the command is skipped.
+
+```yaml
+tasks:
+  build:
+    cmds:
+      # Only run in production
+      - cmd: echo "Optimizing for production"
+        if: '[ "$ENV" = "production" ]'
+      # Using Go templates
+      - cmd: echo "Feature enabled"
+        if: '{{eq .ENABLE_FEATURE "true"}}'
+      # Inside for loops (evaluated per iteration)
+      - for: [a, b, c]
+        cmd: echo "processing {{.ITEM}}"
+        if: '[ "{{.ITEM}}" != "b" ]'
+```
+
 ## Shell Options
 
 ### Set Options