Merge pull request #1359 from afbjorklund/start-yq

Add builtin yq support to lima start command

Author: AkihiroSuda

README.md

@@ -176,6 +176,11 @@ $ limactl start --name=default template://docker
 > NOTE: `limactl start template://TEMPLATE` requires Lima v0.9.0 or later.
 > Older releases require `limactl start /usr/local/share/doc/lima/examples/TEMPLATE.yaml` instead.
 
+To create an instance "default" with modified parameters:
+```console
+$ limactl start --set='.cpus = 2 | .memory = "2GiB"'
+```
+
 To see the template list:
 ```console
 $ limactl start --list-templates

cmd/limactl/start.go

@@ -21,6 +21,7 @@ import (
 	"github.com/lima-vm/lima/pkg/store"
 	"github.com/lima-vm/lima/pkg/store/filenames"
 	"github.com/lima-vm/lima/pkg/templatestore"
+	"github.com/lima-vm/lima/pkg/yqutil"
 	"github.com/mattn/go-isatty"
 	"github.com/sirupsen/logrus"
 	"github.com/spf13/cobra"
@@ -36,6 +37,9 @@ $ limactl start
 To create an instance "default" from a template "docker":
 $ limactl start --name=default template://docker
 
+To create an instance "default" with modified parameters:
+$ limactl start --set='.cpus = 2 | .memory = "2GiB"'
+
 To see the template list:
 $ limactl start --list-templates
 
@@ -56,6 +60,7 @@ $ cat template.yaml | limactl start --name=local -
 	// TODO: "survey" does not support using cygwin terminal on windows yet
 	startCommand.Flags().Bool("tty", isatty.IsTerminal(os.Stdout.Fd()), "enable TUI interactions such as opening an editor, defaults to true when stdout is a terminal")
 	startCommand.Flags().String("name", "", "override the instance name")
+	startCommand.Flags().String("set", "", "modify the template inplace, using yq syntax")
 	startCommand.Flags().Bool("list-templates", false, "list available templates and exit")
 	startCommand.Flags().Duration("timeout", start.DefaultWatchHostAgentEventsTimeout, "duration to wait for the instance to be running before timing out")
 	return startCommand
@@ -82,6 +87,10 @@ func loadOrCreateInstance(cmd *cobra.Command, args []string) (*store.Instance, e
 	if err != nil {
 		return nil, err
 	}
+	st.yq, err = cmd.Flags().GetString("set")
+	if err != nil {
+		return nil, err
+	}
 	const yBytesLimit = 4 * 1024 * 1024 // 4MiB
 
 	if ok, u := guessarg.SeemsTemplateURL(arg); ok {
@@ -206,6 +215,9 @@ func loadOrCreateInstance(cmd *cobra.Command, args []string) (*store.Instance, e
 		}
 	} else {
 		logrus.Info("Terminal is not available, proceeding without opening an editor")
+		if err := modifyInPlace(st); err != nil {
+			return nil, err
+		}
 	}
 	saveBrokenEditorBuffer := tty
 	return createInstance(st, saveBrokenEditorBuffer)
@@ -261,10 +273,27 @@ func createInstance(st *creatorState, saveBrokenEditorBuffer bool) (*store.Insta
 type creatorState struct {
 	instName string // instance name
 	yBytes   []byte // yaml bytes
+	yq       string // yq expression
+}
+
+func modifyInPlace(st *creatorState) error {
+	if st.yq == "" {
+		return nil
+	}
+	out, err := yqutil.EvaluateExpression(st.yq, st.yBytes)
+	if err != nil {
+		return err
+	}
+	st.yBytes = out
+	return nil
 }
 
 func chooseNextCreatorState(st *creatorState) (*creatorState, error) {
 	for {
+		if err := modifyInPlace(st); err != nil {
+			logrus.WithError(err).Warn("Failed to evaluate yq expression")
+			return st, err
+		}
 		var ans string
 		prompt := &survey.Select{
 			Message: fmt.Sprintf("Creating an instance %q", st.instName),

docs/experimental.md

@@ -6,3 +6,7 @@ The following features are experimental and subject to change:
 - `vmType: vz` and relevant configurations (`mountType: virtiofs`, `rosetta`, `[]networks.vzNAT`)
 - `arch: riscv64`
 - `video.display: vnc` and relevant configuration (`video.vnc.display`)
+
+The following flags are experimental and subject to change:
+
+- `start --set`, yq expression

go.mod

@@ -26,6 +26,7 @@ require (
 	github.com/mattn/go-isatty v0.0.17
 	github.com/mattn/go-shellwords v1.0.12
 	github.com/miekg/dns v1.1.50
+	github.com/mikefarah/yq/v4 v4.30.8
 	github.com/norouter/norouter v0.6.3
 	github.com/nxadm/tail v1.4.8
 	github.com/opencontainers/go-digest v1.0.0
@@ -35,6 +36,7 @@ require (
 	github.com/xorcare/pointer v1.2.2
 	golang.org/x/sync v0.1.0
 	golang.org/x/sys v0.5.0
+	gopkg.in/op/go-logging.v1 v1.0.0-20160211212156-b2cb9fa56473
 	gotest.tools/v3 v3.4.0
 	inet.af/tcpproxy v0.0.0-20220326234310-be3ee21c9fa0
 	k8s.io/api v0.26.1
@@ -45,9 +47,13 @@ require (
 require (
 	github.com/Microsoft/go-winio v0.5.2 // indirect
 	github.com/VividCortex/ewma v1.1.1 // indirect
+	github.com/a8m/envsubst v1.3.0 // indirect
+	github.com/alecthomas/participle/v2 v2.0.0-beta.5 // indirect
 	github.com/apparentlymart/go-cidr v1.1.0 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/digitalocean/go-libvirt v0.0.0-20201209184759-e2a69bcd5bd1 // indirect
+	github.com/dimchansky/utfbom v1.1.1 // indirect
+	github.com/elliotchance/orderedmap v1.5.0 // indirect
 	github.com/emicklei/go-restful/v3 v3.9.0 // indirect
 	github.com/evanphx/json-patch v4.12.0+incompatible // indirect
 	github.com/fatih/color v1.13.0 // indirect
@@ -56,6 +62,7 @@ require (
 	github.com/go-openapi/jsonpointer v0.19.5 // indirect
 	github.com/go-openapi/jsonreference v0.20.0 // indirect
 	github.com/go-openapi/swag v0.19.14 // indirect
+	github.com/goccy/go-json v0.10.0 // indirect
 	github.com/gogo/protobuf v1.3.2 // indirect
 	github.com/golang/protobuf v1.5.2 // indirect
 	github.com/google/btree v1.0.1 // indirect
@@ -66,10 +73,12 @@ require (
 	github.com/imdario/mergo v0.3.12 // indirect
 	github.com/inconshreveable/mousetrap v1.0.1 // indirect
 	github.com/insomniacslk/dhcp v0.0.0-20220504074936-1ca156eafb9f // indirect
+	github.com/jinzhu/copier v0.3.5 // indirect
 	github.com/josharian/intern v1.0.0 // indirect
 	github.com/json-iterator/go v1.1.12 // indirect
 	github.com/kballard/go-shellquote v0.0.0-20180428030007-95032a82bc51 // indirect
 	github.com/kr/fs v0.1.0 // indirect
+	github.com/magiconair/properties v1.8.7 // indirect
 	github.com/mailru/easyjson v0.7.6 // indirect
 	github.com/mattn/go-colorable v0.1.12 // indirect
 	github.com/mattn/go-runewidth v0.0.12 // indirect

go.sum

@@ -62,6 +62,12 @@ github.com/PuerkitoBio/purell v1.0.0/go.mod h1:c11w/QuzBsJSee3cPx9rAFu61PvFxuPbt
 github.com/PuerkitoBio/urlesc v0.0.0-20160726150825-5bd2802263f2/go.mod h1:uGdkoq3SwY9Y+13GIhn11/XLaGBb4BfwItxLd5jeuXE=
 github.com/VividCortex/ewma v1.1.1 h1:MnEK4VOv6n0RSY4vtRe3h11qjxL3+t0B8yOL8iMXdcM=
 github.com/VividCortex/ewma v1.1.1/go.mod h1:2Tkkvm3sRDVXaiyucHiACn4cqf7DpdyLvmxzcbUokwA=
+github.com/a8m/envsubst v1.3.0 h1:GmXKmVssap0YtlU3E230W98RWtWCyIZzjtf1apWWyAg=
+github.com/a8m/envsubst v1.3.0/go.mod h1:MVUTQNGQ3tsjOOtKCNd+fl8RzhsXcDvvAEzkhGtlsbY=
+github.com/alecthomas/assert/v2 v2.0.3 h1:WKqJODfOiQG0nEJKFKzDIG3E29CN2/4zR9XGJzKIkbg=
+github.com/alecthomas/participle/v2 v2.0.0-beta.5 h1:y6dsSYVb1G5eK6mgmy+BgI3Mw35a3WghArZ/Hbebrjo=
+github.com/alecthomas/participle/v2 v2.0.0-beta.5/go.mod h1:RC764t6n4L8D8ITAJv0qdokritYSNR3wV5cVwmIEaMM=
+github.com/alecthomas/repr v0.2.0 h1:HAzS41CIzNW5syS8Mf9UwXhNH1J9aix/BvDRf1Ml2Yk=
 github.com/alecthomas/template v0.0.0-20160405071501-a0175ee3bccc/go.mod h1:LOuyumcjzFXgccqObfd/Ljyb9UuFJ6TxHnclSeseNhc=
 github.com/alecthomas/units v0.0.0-20151022065526-2efee857e7cf/go.mod h1:ybxpYRFXyAe+OPACYpWeL0wqObRcbAqCMya13uyzqw0=
 github.com/alessio/shellescape v1.4.1 h1:V7yhSDDn8LP4lc4jS8pFkt0zCnzVJlG5JXy9BVKJUX0=
@@ -161,6 +167,8 @@ github.com/digitalocean/go-libvirt v0.0.0-20201209184759-e2a69bcd5bd1 h1:j6vGfla
 github.com/digitalocean/go-libvirt v0.0.0-20201209184759-e2a69bcd5bd1/go.mod h1:QS1XzqZLcDniNYrN7EZefq3wIyb/M2WmJbql4ZKoc1Q=
 github.com/digitalocean/go-qemu v0.0.0-20210326154740-ac9e0b687001 h1:WAg57gnaAWWjMAELcwHjc2xy0PoXQ5G+vn3+XS6s1jI=
 github.com/digitalocean/go-qemu v0.0.0-20210326154740-ac9e0b687001/go.mod h1:IetBE52JfFxK46p2n2Rqm+p5Gx1gpu2hRHsrbnPOWZQ=
+github.com/dimchansky/utfbom v1.1.1 h1:vV6w1AhK4VMnhBno/TPVCoK9U/LP0PkLCS9tbxHdi/U=
+github.com/dimchansky/utfbom v1.1.1/go.mod h1:SxdoEBH5qIqFocHMyGOXVAybYJdr71b1Q/j0mACtrfE=
 github.com/diskfs/go-diskfs v1.3.0 h1:D3IVe1y7ybB5SjCO0pOmkWThL9lZEWeanp8rRa0q0sk=
 github.com/diskfs/go-diskfs v1.3.0/go.mod h1:3pUpCAz75Q11om5RsGpVKUgXp2Z+ATw1xV500glmCP0=
 github.com/docker/distribution v2.7.1-0.20190205005809-0d3efadf0154+incompatible/go.mod h1:J2gT2udsDAN96Uj4KfcMRqY0/ypR+oyYUYmja8H+y+w=
@@ -178,6 +186,8 @@ github.com/elastic/go-libaudit/v2 v2.3.2/go.mod h1:+ZE0czqmbqtnRkl0fNgpI+HvVVRo/
 github.com/elazarl/goproxy v0.0.0-20170405201442-c4fc26588b6e/go.mod h1:/Zj4wYkgs4iZTTu3o/KG3Itv/qCCa8VVMlb3i9OVuzc=
 github.com/elazarl/goproxy v0.0.0-20210110162100-a92cc753f88e/go.mod h1:Ro8st/ElPeALwNFlcTpWmkr6IoMFfkjXAvTHpevnDsM=
 github.com/elazarl/goproxy/ext v0.0.0-20190711103511-473e67f1d7d2/go.mod h1:gNh8nYJoAm43RfaxurUnxr+N1PwuFV3ZMl/efxlIlY8=
+github.com/elliotchance/orderedmap v1.5.0 h1:1IsExUsjv5XNBD3ZdC7jkAAqLWOOKdbPTmkHx63OsBg=
+github.com/elliotchance/orderedmap v1.5.0/go.mod h1:wsDwEaX5jEoyhbs7x93zk2H/qv0zwuhg4inXhDkYqys=
 github.com/emicklei/go-restful v0.0.0-20170410110728-ff4f55a20633/go.mod h1:otzb+WCGbkyDHkqmQmT5YD2WR4BBwUdeQoFo8l/7tVs=
 github.com/emicklei/go-restful/v3 v3.9.0 h1:XwGDlfxEnQZzuopoqxwSEllNcCOM9DhhFyhFIIGKwxE=
 github.com/emicklei/go-restful/v3 v3.9.0/go.mod h1:6n3XBCmQQb25CM2LCACGz8ukIrRry+4bhvbpWn3mrbc=
@@ -241,6 +251,8 @@ github.com/go-stack/stack v1.8.0/go.mod h1:v0f6uXyyMGvRgIKkXu+yp6POWl0qKG85gN/me
 github.com/go-task/slim-sprig v0.0.0-20210107165309-348f09dbbbc0/go.mod h1:fyg7847qk6SyHyPtNmDHnmrv/HOrqktSC+C9fM+CJOE=
 github.com/go-test/deep v1.0.8 h1:TDsG77qcSprGbC6vTN8OuXp5g+J+b5Pcguhf7Zt61VM=
 github.com/go-test/deep v1.0.8/go.mod h1:5C2ZWiW0ErCdrYzpqxLbTX7MG14M9iiw8DgHncVwcsE=
+github.com/goccy/go-json v0.10.0 h1:mXKd9Qw4NuzShiRlOXKews24ufknHO7gx30lsDyokKA=
+github.com/goccy/go-json v0.10.0/go.mod h1:6MelG93GURQebXPDq3khkgXZkazVtN9CRI+MGFi0w8I=
 github.com/goccy/go-yaml v1.9.8 h1:5gMyLUeU1/6zl+WFfR1hN7D2kf+1/eRGa7DFtToiBvQ=
 github.com/goccy/go-yaml v1.9.8/go.mod h1:JubOolP3gh0HpiBc4BLRD4YmjEjHAmIIB2aaXKkTfoE=
 github.com/godbus/dbus/v5 v5.0.3/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
@@ -358,6 +370,7 @@ github.com/hashicorp/go-multierror v1.1.1/go.mod h1:iw975J/qwKPdAO1clOe2L8331t/9
 github.com/hashicorp/golang-lru v0.5.0/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ4Ao+sR/qLZy8=
 github.com/hashicorp/golang-lru v0.5.1/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ4Ao+sR/qLZy8=
 github.com/hashicorp/hcl v1.0.0/go.mod h1:E5yfLk+7swimpb2L/Alb/PJmXilQ/rhwaUYs4T20WEQ=
+github.com/hexops/gotextdiff v1.0.3 h1:gitA9+qJrrTCsiCl7+kh75nPqQt1cx4ZkudSTLoUqJM=
 github.com/hinshun/vt10x v0.0.0-20220119200601-820417d04eec h1:qv2VnGeEQHchGaZ/u7lxST/RaJw+cv273q79D81Xbog=
 github.com/hinshun/vt10x v0.0.0-20220119200601-820417d04eec/go.mod h1:Q48J4R4DvxnHolD5P8pOtXigYlRuPLGl6moFx3ulM68=
 github.com/hpcloud/tail v1.0.0/go.mod h1:ab1qPbhIpdTxEkNHXyeSf5vhxWSCs/tWer42PpOxQnU=
@@ -372,6 +385,8 @@ github.com/inconshreveable/mousetrap v1.0.1 h1:U3uMjPSQEBMNp1lFxmllqCPM6P5u/Xq7P
 github.com/inconshreveable/mousetrap v1.0.1/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
 github.com/insomniacslk/dhcp v0.0.0-20220504074936-1ca156eafb9f h1:l1QCwn715k8nYkj4Ql50rzEog3WnMdrd4YYMMwemxEo=
 github.com/insomniacslk/dhcp v0.0.0-20220504074936-1ca156eafb9f/go.mod h1:h+MxyHxRg9NH3terB1nfRIUaQEcI0XOVkdR9LNBlp8E=
+github.com/jinzhu/copier v0.3.5 h1:GlvfUwHk62RokgqVNvYsku0TATCF7bAHVwEXoBh3iJg=
+github.com/jinzhu/copier v0.3.5/go.mod h1:DfbEm0FYsaqBcKcFuvmOZb218JkPGtvSHsKg8S8hyyg=
 github.com/jonboulle/clockwork v0.1.0/go.mod h1:Ii8DK3G1RaLaWxj9trq07+26W01tbo22gdxWY5EU2bo=
 github.com/josharian/intern v1.0.0 h1:vlS4z54oSdjm0bgjRigI+G1HpF+tI+9rE5LLzOg8HmY=
 github.com/josharian/intern v1.0.0/go.mod h1:5DoeVV0s6jJacbCEi61lwdGj/aVlrQvzHFFd8Hwg//Y=
@@ -414,6 +429,8 @@ github.com/linuxkit/virtsock v0.0.0-20220523201153-1a23e78aa7a2/go.mod h1:SWzULI
 github.com/lithammer/dedent v1.1.0 h1:VNzHMVCBNG1j0fh3OrsFRkVUwStdDArbgBWoPAffktY=
 github.com/lithammer/dedent v1.1.0/go.mod h1:jrXYCQtgg0nJiN+StA2KgR7w6CiQNv9Fd/Z9BP0jIOc=
 github.com/magiconair/properties v1.8.0/go.mod h1:PppfXfuXeibc/6YijjN8zIbojt8czPbwD3XqdrwzmxQ=
+github.com/magiconair/properties v1.8.7 h1:IeQXZAiQcpL9mgcAe1Nu6cX9LLw6ExEHKjN0VQdvPDY=
+github.com/magiconair/properties v1.8.7/go.mod h1:Dhd985XPs7jluiymwWYZ0G4Z61jb3vdS329zhj2hYo0=
 github.com/mailru/easyjson v0.0.0-20160728113105-d5b7844b561a/go.mod h1:C1wdFJiN94OJF2b5HbByQZoLdCWB1Yqtg26g4irojpc=
 github.com/mailru/easyjson v0.0.0-20190614124828-94de47d64c63/go.mod h1:C1wdFJiN94OJF2b5HbByQZoLdCWB1Yqtg26g4irojpc=
 github.com/mailru/easyjson v0.0.0-20190626092158-b2ccc519800e/go.mod h1:C1wdFJiN94OJF2b5HbByQZoLdCWB1Yqtg26g4irojpc=
@@ -452,6 +469,8 @@ github.com/miekg/dns v1.1.25/go.mod h1:bPDLeHnStXmXAq1m/Ch/hvfNHr14JKNPMBo3VZKju
 github.com/miekg/dns v1.1.41/go.mod h1:p6aan82bvRIyn+zDIv9xYNUpwa73JcSh9BKwknJysuI=
 github.com/miekg/dns v1.1.50 h1:DQUfb9uc6smULcREF09Uc+/Gd46YWqJd5DbpPE9xkcA=
 github.com/miekg/dns v1.1.50/go.mod h1:e3IlAVfNqAllflbibAZEWOXOQ+Ynzk/dDozDxY7XnME=
+github.com/mikefarah/yq/v4 v4.30.8 h1:EHovseqMJs9kvE25/2k6VnDs4CrBZN+DFbybUhpPAGM=
+github.com/mikefarah/yq/v4 v4.30.8/go.mod h1:8D30GDxhu3+KXll0aFV5msGcdgYRZSPOPVBTbgUQ7Dc=
 github.com/mitchellh/go-homedir v1.1.0/go.mod h1:SfyaCUpYCn1Vlf4IUYiD9fPX4A5wJrkLzIz1N1q0pr0=
 github.com/mitchellh/mapstructure v1.1.2/go.mod h1:FVVH3fgwuzCH5S8UJGiWEs2h04kUh9fWfEaFds41c1Y=
 github.com/modern-go/concurrent v0.0.0-20180228061459-e0a39a4cb421/go.mod h1:6dJC0mAP4ikYIbvyc7fijjWJddQyLn8Ig3JB5CqoB9Q=
@@ -510,6 +529,7 @@ github.com/pborman/uuid v1.2.0/go.mod h1:X/NO0urCmaxf9VXbdlT7C2Yzkj2IKimNn4k+gtP
 github.com/pelletier/go-toml v1.2.0/go.mod h1:5z9KED0ma1S8pY6P1sdut58dfprrGBbd/94hg7ilaic=
 github.com/peterbourgon/diskv v2.0.1+incompatible/go.mod h1:uqqh8zWWbv1HBMNONnaR/tNboyR3/BZd58JJSHlUSCU=
 github.com/pierrec/lz4 v2.3.0+incompatible/go.mod h1:pdkljMzZIN41W+lC3N2tnIh5sFi+IEE17M5jbnwPHcY=
+github.com/pkg/diff v0.0.0-20210226163009-20ebb0f2a09e h1:aoZm08cpOy4WuID//EZDgcC4zIxODThtZNPirFr42+A=
 github.com/pkg/errors v0.8.0/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pkg/errors v0.8.1-0.20170910134614-2b3a18b5f0fb/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
@@ -1067,6 +1087,8 @@ gopkg.in/errgo.v2 v2.1.0/go.mod h1:hNsd1EY+bozCKY1Ytp96fpM3vjJbqLJn88ws8XvfDNI=
 gopkg.in/fsnotify.v1 v1.4.7/go.mod h1:Tz8NjZHkW78fSQdbUxIjBTcgA1z1m8ZHf0WmKUhAMys=
 gopkg.in/inf.v0 v0.9.1 h1:73M5CoZyi3ZLMOyDlQh031Cx6N9NDJ2Vvfl76EDAgDc=
 gopkg.in/inf.v0 v0.9.1/go.mod h1:cWUDdTG/fYaXco+Dcufb5Vnc6Gp2YChqWtbxRZE0mXw=
+gopkg.in/op/go-logging.v1 v1.0.0-20160211212156-b2cb9fa56473 h1:6D+BvnJ/j6e222UW8s2qTSe3wGBtvo0MbVQG/c5k8RE=
+gopkg.in/op/go-logging.v1 v1.0.0-20160211212156-b2cb9fa56473/go.mod h1:N1eN2tsCx0Ydtgjl4cqmbRCsY4/+z4cYDeqwZTk6zog=
 gopkg.in/resty.v1 v1.12.0/go.mod h1:mDo4pnntr5jdWRML875a/NmxYqAlA73dVijT2AXvQQo=
 gopkg.in/tomb.v1 v1.0.0-20141024135613-dd632973f1e7 h1:uRGJdciOHaEIrze2W8Q3AKkepLTh2hOroT7a+7czfdQ=
 gopkg.in/tomb.v1 v1.0.0-20141024135613-dd632973f1e7/go.mod h1:dt/ZhP58zS4L8KSrWDmTeBkI65Dw0HsyUHuEVlX15mw=

pkg/yqutil/yqutil.go

@@ -0,0 +1,66 @@
+package yqutil
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+
+	"github.com/mikefarah/yq/v4/pkg/yqlib"
+	"github.com/sirupsen/logrus"
+	logging "gopkg.in/op/go-logging.v1"
+)
+
+// EvaluateExpression evaluates the yq expression, and returns the modified yaml.
+func EvaluateExpression(expression string, content []byte) ([]byte, error) {
+	tmpYAMLFile, err := os.CreateTemp("", "lima-yq-*.yaml")
+	if err != nil {
+		return nil, err
+	}
+	tmpYAMLPath := tmpYAMLFile.Name()
+	defer os.RemoveAll(tmpYAMLPath)
+	err = os.WriteFile(tmpYAMLPath, content, 0o600)
+	if err != nil {
+		return nil, err
+	}
+
+	memory := logging.NewMemoryBackend(0)
+	backend := logging.AddModuleLevel(memory)
+	logging.SetBackend(backend)
+	yqlib.InitExpressionParser()
+
+	indent := 2
+	encoder := yqlib.NewYamlEncoder(indent, false, yqlib.ConfiguredYamlPreferences)
+	out := new(bytes.Buffer)
+	printer := yqlib.NewPrinter(encoder, yqlib.NewSinglePrinterWriter(out))
+	decoder := yqlib.NewYamlDecoder(yqlib.ConfiguredYamlPreferences)
+
+	streamEvaluator := yqlib.NewStreamEvaluator()
+	files := []string{tmpYAMLPath}
+	err = streamEvaluator.EvaluateFiles(expression, files, printer, decoder)
+	if err != nil {
+		logger := logrus.StandardLogger()
+		for node := memory.Head(); node != nil; node = node.Next() {
+			entry := logrus.NewEntry(logger).WithTime(node.Record.Time)
+			prefix := fmt.Sprintf("[%s] ", node.Record.Module)
+			message := prefix + node.Record.Message()
+			switch node.Record.Level {
+			case logging.CRITICAL:
+				entry.Fatal(message)
+			case logging.ERROR:
+				entry.Error(message)
+			case logging.WARNING:
+				entry.Warn(message)
+			case logging.NOTICE:
+				entry.Info(message)
+			case logging.INFO:
+				entry.Info(message)
+			case logging.DEBUG:
+				entry.Debug(message)
+			}
+		}
+		return nil, err
+	}
+
+	return out.Bytes(), nil
+
+}

pkg/yqutil/yqutil_test.go

@@ -0,0 +1,65 @@
+package yqutil
+
+import (
+	"testing"
+
+	"gotest.tools/v3/assert"
+)
+
+func TestEvaluateExpressionSimple(t *testing.T) {
+	expression := `.cpus = 2 | .memory = "2GiB"`
+	content := `
+# CPUs
+cpus: null
+
+# Memory size
+memory: null
+`
+	// Note: yq currently removes empty lines, but not comments
+	expected := `
+# CPUs
+cpus: 2
+# Memory size
+memory: 2GiB
+`
+	out, err := EvaluateExpression(expression, []byte(content))
+	assert.NilError(t, err)
+	assert.Equal(t, expected, string(out))
+}
+
+func TestEvaluateExpressionComplex(t *testing.T) {
+	expression := `.mounts += {"location": "foo", "mountPoint": "bar"}`
+	content := `
+# Expose host directories to the guest, the mount point might be accessible from all UIDs in the guest
+# 🟢 Builtin default: null (Mount nothing)
+# 🔵 This file: Mount the home as read-only, /tmp/lima as writable
+mounts:
+- location: "~"
+  # Configure the mountPoint inside the guest.
+  # 🟢 Builtin default: value of location
+  mountPoint: null
+`
+	// Note: yq will use canonical yaml, with indented sequences
+	// Note: yq will not explicitly quote strings, when not needed
+	expected := `
+# Expose host directories to the guest, the mount point might be accessible from all UIDs in the guest
+# 🟢 Builtin default: null (Mount nothing)
+# 🔵 This file: Mount the home as read-only, /tmp/lima as writable
+mounts:
+  - location: "~"
+    # Configure the mountPoint inside the guest.
+    # 🟢 Builtin default: value of location
+    mountPoint: null
+  - location: foo
+    mountPoint: bar
+`
+	out, err := EvaluateExpression(expression, []byte(content))
+	assert.NilError(t, err)
+	assert.Equal(t, expected, string(out))
+}
+
+func TestEvaluateExpressionError(t *testing.T) {
+	expression := `arch: aarch64`
+	_, err := EvaluateExpression(expression, []byte(""))
+	assert.ErrorContains(t, err, "invalid input text")
+}