feat(cli): lotus chain head --height to print epoch number

A simpler version of what's currently possible with:

	lotus chain list --format '<height>' --count 1

Author: rvagg

CHANGELOG.md

@@ -7,6 +7,7 @@
 - Reduce size of embedded genesis CAR files by removing WASM actor blocks and compressing with zstd. This reduces the `lotus` binary size by approximately 10 MiB. ([filecoin-project/lotus#12439](https://github.com/filecoin-project/lotus/pull/12439))
 - Add ChainSafe operated Calibration archival node to the bootstrap list ([filecoin-project/lotus#12517](https://github.com/filecoin-project/lotus/pull/12517))
 - Fix hotloop in F3 pariticpation API ([filecoin-project/lotus#12575](https://github.com/filecoin-project/lotus/pull/12575))
+- `lotus chain head` now supports a `--height` flag to print just the epoch number of the current chain head ([filecoin-project/lotus#12609](https://github.com/filecoin-project/lotus/pull/12609))
 
 ## Bug Fixes
 - Fix a bug in the `lotus-shed indexes backfill-events` command that may result in either duplicate events being backfilled where there are existing events (such an operation *should* be idempotent) or events erroneously having duplicate `logIndex` values when queried via ETH APIs. ([filecoin-project/lotus#12567](https://github.com/filecoin-project/lotus/pull/12567))
@@ -15,8 +16,6 @@
 
 ## Improvements
 
-## Improvements
-
 ## Deps
 
 # UNRELEASED Node v1.30.0  

cli/chain.go

@@ -72,6 +72,12 @@ var ChainCmd = &cli.Command{
 var ChainHeadCmd = &cli.Command{
 	Name:  "head",
 	Usage: "Print chain head",
+	Flags: []cli.Flag{
+		&cli.BoolFlag{
+			Name:  "height",
+			Usage: "print just the epoch number of the chain head",
+		},
+	},
 	Action: func(cctx *cli.Context) error {
 		afmt := NewAppFmt(cctx.App)
 
@@ -87,8 +93,12 @@ var ChainHeadCmd = &cli.Command{
 			return err
 		}
 
-		for _, c := range head.Cids() {
-			afmt.Println(c)
+		if cctx.Bool("height") {
+			afmt.Println(head.Height())
+		} else {
+			for _, c := range head.Cids() {
+				afmt.Println(c)
+			}
 		}
 		return nil
 	},

documentation/en/cli-lotus.md

@@ -1616,6 +1616,7 @@ USAGE:
    lotus chain head [command options] [arguments...]
 
 OPTIONS:
+   --height    print just the epoch number of the chain head (default: false)
    --help, -h  show help
 ```