Experiment with mlr script (#2009)

docs/src/manpage.md

@@ -246,7 +246,7 @@ This is simply a copy of what you should see on running `man mlr` at a command p
        is_numeric is_present is_string joink joinkv joinv json_parse json_stringify
        kurtosis latin1_to_utf8 leafcount leftpad length localtime2gmt localtime2nsec
        localtime2sec log log10 log1p logifit lstrip madd mapdiff mapexcept mapselect
-       mapsum max maxlen md5 mean meaneb median mexp min minlen mmul mode msub
+       mapsum max maxlen md5 mean meaneb median mexp min minlen mmul mode msub next
        nsec2gmt nsec2gmtdate nsec2localdate nsec2localtime null_count os percentile
        percentiles pow qnorm reduce regextract regextract_or_else rightpad round
        roundm rstrip sec2dhms sec2gmt sec2gmtdate sec2hms sec2localdate sec2localtime
@@ -2825,6 +2825,9 @@ This is simply a copy of what you should see on running `man mlr` at a command p
    1mmsub0m
         (class=arithmetic #args=3) a - b mod m (integers)
 
+   1mnext0m
+        (class=system #args=0) In mlr script mode only: reads the next record from input. Returns true if a record was read (and sets $* to it), false at end of stream (and $* becomes false).
+
    1mnsec2gmt0m
         (class=time #args=1,2) Formats integer nanoseconds since epoch as GMT timestamp. Leaves non-numbers as-is. With second integer argument n, includes n decimal places for the seconds part.
        Examples:
@@ -3817,5 +3820,5 @@ This is simply a copy of what you should see on running `man mlr` at a command p
        MIME Type for Comma-Separated Values (CSV) Files, the Miller docsite
        https://miller.readthedocs.io
 
-                                  2026-03-03                         4mMILLER24m(1)
+                                  2026-03-06                         4mMILLER24m(1)
 </pre>

docs/src/manpage.txt

@@ -225,7 +225,7 @@
        is_numeric is_present is_string joink joinkv joinv json_parse json_stringify
        kurtosis latin1_to_utf8 leafcount leftpad length localtime2gmt localtime2nsec
        localtime2sec log log10 log1p logifit lstrip madd mapdiff mapexcept mapselect
-       mapsum max maxlen md5 mean meaneb median mexp min minlen mmul mode msub
+       mapsum max maxlen md5 mean meaneb median mexp min minlen mmul mode msub next
        nsec2gmt nsec2gmtdate nsec2localdate nsec2localtime null_count os percentile
        percentiles pow qnorm reduce regextract regextract_or_else rightpad round
        roundm rstrip sec2dhms sec2gmt sec2gmtdate sec2hms sec2localdate sec2localtime
@@ -2804,6 +2804,9 @@
    1mmsub0m
         (class=arithmetic #args=3) a - b mod m (integers)
 
+   1mnext0m
+        (class=system #args=0) In mlr script mode only: reads the next record from input. Returns true if a record was read (and sets $* to it), false at end of stream (and $* becomes false).
+
    1mnsec2gmt0m
         (class=time #args=1,2) Formats integer nanoseconds since epoch as GMT timestamp. Leaves non-numbers as-is. With second integer argument n, includes n decimal places for the seconds part.
        Examples:
@@ -3796,4 +3799,4 @@
        MIME Type for Comma-Separated Values (CSV) Files, the Miller docsite
        https://miller.readthedocs.io
 
-                                  2026-03-03                         4mMILLER24m(1)
+                                  2026-03-06                         4mMILLER24m(1)

docs/src/reference-dsl-builtin-functions.md

@@ -61,7 +61,7 @@ Operators are listed here along with functions. In this case, the argument count
 * [**Math functions**](#math-functions):  [abs](#abs),  [acos](#acos),  [acosh](#acosh),  [asin](#asin),  [asinh](#asinh),  [atan](#atan),  [atan2](#atan2),  [atanh](#atanh),  [cbrt](#cbrt),  [ceil](#ceil),  [cos](#cos),  [cosh](#cosh),  [erf](#erf),  [erfc](#erfc),  [exp](#exp),  [expm1](#expm1),  [floor](#floor),  [invqnorm](#invqnorm),  [log](#log),  [log10](#log10),  [log1p](#log1p),  [logifit](#logifit),  [max](#max),  [min](#min),  [qnorm](#qnorm),  [round](#round),  [roundm](#roundm),  [sgn](#sgn),  [sin](#sin),  [sinh](#sinh),  [sqrt](#sqrt),  [tan](#tan),  [tanh](#tanh),  [urand](#urand),  [urand32](#urand32),  [urandelement](#urandelement),  [urandint](#urandint),  [urandrange](#urandrange).
 * [**Stats functions**](#stats-functions):  [antimode](#antimode),  [count](#count),  [distinct_count](#distinct_count),  [kurtosis](#kurtosis),  [maxlen](#maxlen),  [mean](#mean),  [meaneb](#meaneb),  [median](#median),  [minlen](#minlen),  [mode](#mode),  [null_count](#null_count),  [percentile](#percentile),  [percentiles](#percentiles),  [skewness](#skewness),  [sort_collection](#sort_collection),  [stddev](#stddev),  [sum](#sum),  [sum2](#sum2),  [sum3](#sum3),  [sum4](#sum4),  [variance](#variance).
 * [**String functions**](#string-functions):  [capitalize](#capitalize),  [clean_whitespace](#clean_whitespace),  [collapse_whitespace](#collapse_whitespace),  [contains](#contains),  [format](#format),  [gssub](#gssub),  [gsub](#gsub),  [index](#index),  [latin1_to_utf8](#latin1_to_utf8),  [leftpad](#leftpad),  [lstrip](#lstrip),  [regextract](#regextract),  [regextract_or_else](#regextract_or_else),  [rightpad](#rightpad),  [rstrip](#rstrip),  [ssub](#ssub),  [strip](#strip),  [strlen](#strlen),  [strmatch](#strmatch),  [strmatchx](#strmatchx),  [sub](#sub),  [substr](#substr),  [substr0](#substr0),  [substr1](#substr1),  [tolower](#tolower),  [toupper](#toupper),  [truncate](#truncate),  [unformat](#unformat),  [unformatx](#unformatx),  [utf8_to_latin1](#utf8_to_latin1),  [\.](#dot).
-* [**System functions**](#system-functions):  [exec](#exec),  [hostname](#hostname),  [os](#os),  [stat](#stat),  [system](#system),  [version](#version).
+* [**System functions**](#system-functions):  [exec](#exec),  [hostname](#hostname),  [next](#next),  [os](#os),  [stat](#stat),  [system](#system),  [version](#version).
 * [**Time functions**](#time-functions):  [dhms2fsec](#dhms2fsec),  [dhms2sec](#dhms2sec),  [fsec2dhms](#fsec2dhms),  [fsec2hms](#fsec2hms),  [gmt2localtime](#gmt2localtime),  [gmt2nsec](#gmt2nsec),  [gmt2sec](#gmt2sec),  [hms2fsec](#hms2fsec),  [hms2sec](#hms2sec),  [localtime2gmt](#localtime2gmt),  [localtime2nsec](#localtime2nsec),  [localtime2sec](#localtime2sec),  [nsec2gmt](#nsec2gmt),  [nsec2gmtdate](#nsec2gmtdate),  [nsec2localdate](#nsec2localdate),  [nsec2localtime](#nsec2localtime),  [sec2dhms](#sec2dhms),  [sec2gmt](#sec2gmt),  [sec2gmtdate](#sec2gmtdate),  [sec2hms](#sec2hms),  [sec2localdate](#sec2localdate),  [sec2localtime](#sec2localtime),  [strfntime](#strfntime),  [strfntime_local](#strfntime_local),  [strftime](#strftime),  [strftime_local](#strftime_local),  [strpntime](#strpntime),  [strpntime_local](#strpntime_local),  [strptime](#strptime),  [strptime_local](#strptime_local),  [sysntime](#sysntime),  [systime](#systime),  [systimeint](#systimeint),  [upntime](#upntime),  [uptime](#uptime).
 * [**Typing functions**](#typing-functions):  [asserting_absent](#asserting_absent),  [asserting_array](#asserting_array),  [asserting_bool](#asserting_bool),  [asserting_boolean](#asserting_boolean),  [asserting_empty](#asserting_empty),  [asserting_empty_map](#asserting_empty_map),  [asserting_error](#asserting_error),  [asserting_float](#asserting_float),  [asserting_int](#asserting_int),  [asserting_map](#asserting_map),  [asserting_nonempty_map](#asserting_nonempty_map),  [asserting_not_array](#asserting_not_array),  [asserting_not_empty](#asserting_not_empty),  [asserting_not_map](#asserting_not_map),  [asserting_not_null](#asserting_not_null),  [asserting_null](#asserting_null),  [asserting_numeric](#asserting_numeric),  [asserting_present](#asserting_present),  [asserting_string](#asserting_string),  [is_absent](#is_absent),  [is_array](#is_array),  [is_bool](#is_bool),  [is_boolean](#is_boolean),  [is_empty](#is_empty),  [is_empty_map](#is_empty_map),  [is_error](#is_error),  [is_float](#is_float),  [is_int](#is_int),  [is_map](#is_map),  [is_nan](#is_nan),  [is_nonempty_map](#is_nonempty_map),  [is_not_array](#is_not_array),  [is_not_empty](#is_not_empty),  [is_not_map](#is_not_map),  [is_not_null](#is_not_null),  [is_null](#is_null),  [is_numeric](#is_numeric),  [is_present](#is_present),  [is_string](#is_string),  [typeof](#typeof).
 
@@ -1481,6 +1481,12 @@ hostname  (class=system #args=0) Returns the hostname as a string.
 </pre>
 
 
+### next
+<pre class="pre-non-highlight-non-pair">
+next  (class=system #args=0) In mlr script mode only: reads the next record from input. Returns true if a record was read (and sets $* to it), false at end of stream (and $* becomes false).
+</pre>
+
+
 ### os
 <pre class="pre-non-highlight-non-pair">
 os  (class=system #args=0) Returns the operating-system name as a string.

docs/src/reference-dsl-differences.md

@@ -68,7 +68,7 @@ mlr: Parse error on token "$y" at line 6 column 3.
 Please check for missing semicolon.
 Expected one of:
   ␚ ; > >> | ? || ^^ && =~ !=~ == != <=> >= < <= ^ & << >>> + - .+ .- *
-  / // % .* ./ .// . ?? ??? ** [ [[ [[[
+  / // % .* ./ .// . ?? ??? ** [
 
 </pre>
 

man/manpage.txt

@@ -225,7 +225,7 @@
        is_numeric is_present is_string joink joinkv joinv json_parse json_stringify
        kurtosis latin1_to_utf8 leafcount leftpad length localtime2gmt localtime2nsec
        localtime2sec log log10 log1p logifit lstrip madd mapdiff mapexcept mapselect
-       mapsum max maxlen md5 mean meaneb median mexp min minlen mmul mode msub
+       mapsum max maxlen md5 mean meaneb median mexp min minlen mmul mode msub next
        nsec2gmt nsec2gmtdate nsec2localdate nsec2localtime null_count os percentile
        percentiles pow qnorm reduce regextract regextract_or_else rightpad round
        roundm rstrip sec2dhms sec2gmt sec2gmtdate sec2hms sec2localdate sec2localtime
@@ -2804,6 +2804,9 @@
    1mmsub0m
         (class=arithmetic #args=3) a - b mod m (integers)
 
+   1mnext0m
+        (class=system #args=0) In mlr script mode only: reads the next record from input. Returns true if a record was read (and sets $* to it), false at end of stream (and $* becomes false).
+
    1mnsec2gmt0m
         (class=time #args=1,2) Formats integer nanoseconds since epoch as GMT timestamp. Leaves non-numbers as-is. With second integer argument n, includes n decimal places for the seconds part.
        Examples:
@@ -3796,4 +3799,4 @@
        MIME Type for Comma-Separated Values (CSV) Files, the Miller docsite
        https://miller.readthedocs.io
 
-                                  2026-03-03                         4mMILLER24m(1)
+                                  2026-03-06                         4mMILLER24m(1)

man/mlr.1

@@ -2,12 +2,12 @@
 .\"     Title: mlr
 .\"    Author: [see the "AUTHOR" section]
 .\" Generator: ./mkman.rb
-.\"      Date: 2026-03-03
+.\"      Date: 2026-03-06
 .\"    Manual: \ \&
 .\"    Source: \ \&
 .\"  Language: English
 .\"
-.TH "MILLER" "1" "2026-03-03" "\ \&" "\ \&"
+.TH "MILLER" "1" "2026-03-06" "\ \&" "\ \&"
 .\" -----------------------------------------------------------------
 .\" * Portability definitions
 .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -274,7 +274,7 @@ is_nonempty_map is_not_array is_not_empty is_not_map is_not_null is_null
 is_numeric is_present is_string joink joinkv joinv json_parse json_stringify
 kurtosis latin1_to_utf8 leafcount leftpad length localtime2gmt localtime2nsec
 localtime2sec log log10 log1p logifit lstrip madd mapdiff mapexcept mapselect
-mapsum max maxlen md5 mean meaneb median mexp min minlen mmul mode msub
+mapsum max maxlen md5 mean meaneb median mexp min minlen mmul mode msub next
 nsec2gmt nsec2gmtdate nsec2localdate nsec2localtime null_count os percentile
 percentiles pow qnorm reduce regextract regextract_or_else rightpad round
 roundm rstrip sec2dhms sec2gmt sec2gmtdate sec2hms sec2localdate sec2localtime
@@ -4207,6 +4207,15 @@ mode([3,3,4,4]) is 3
 .fi
 .if n \{\
 .RE
+.SS "next"
+.if n \{\
+.RS 0
+.\}
+.nf
+ (class=system #args=0) In mlr script mode only: reads the next record from input. Returns true if a record was read (and sets $* to it), false at end of stream (and $* becomes false).
+.fi
+.if n \{\
+.RE
 .SS "nsec2gmt"
 .if n \{\
 .RS 0

pkg/dsl/cst/builtin_function_manager.go

@@ -58,6 +58,7 @@ type BuiltinFunctionInfo struct {
 	variadicFunc           bifs.VariadicFunc
 	unaryFuncWithContext   bifs.UnaryFuncWithContext   // asserting_{typename}
 	regexCaptureBinaryFunc bifs.RegexCaptureBinaryFunc // =~ and !=~
+	zaryFuncWithState      ZaryFuncWithState           // next
 	binaryFuncWithState    BinaryFuncWithState         // select, apply, reduce
 	ternaryFuncWithState   TernaryFuncWithState        // fold
 	variadicFuncWithState  VariadicFuncWithState       // sort
@@ -2504,6 +2505,14 @@ Run a command via executable, path, args and environment, yielding its stdout mi
 			help:     `Returns the Miller version as a string.`,
 			zaryFunc: bifs.BIF_version,
 		},
+
+		// next() is for mlr script: reads next record from input, returns true/false.
+		{
+			name:              "next",
+			class:             FUNC_CLASS_SYSTEM,
+			help:              `In mlr script mode only: reads the next record from input. Returns true if a record was read (and sets $* to it), false at end of stream (and $* becomes false).`,
+			zaryFuncWithState: BIF_next,
+		},
 	}
 
 	// Sort the function table.  Useful for online help and autogenned docs / manpage.
@@ -2734,7 +2743,7 @@ func describeNargs(info *BuiltinFunctionInfo) string {
 		return strings.Join(pieces, ",")
 
 	}
-	if info.zaryFunc != nil {
+	if info.zaryFunc != nil || info.zaryFuncWithState != nil {
 		return "0"
 	}
 	if info.unaryFunc != nil {

pkg/dsl/cst/builtin_functions.go

@@ -13,6 +13,23 @@ import (
 	"github.com/johnkerl/miller/v6/pkg/runtime"
 )
 
+// BIF_next is for mlr script: reads next record from input stream.
+func BIF_next(state *runtime.State) *mlrval.Mlrval {
+	if state.NextRecordFunc == nil {
+		return mlrval.FromErrorString("next() is only available in mlr script mode")
+	}
+	record, context, hasMore := state.NextRecordFunc()
+	if hasMore {
+		state.Update(record, context)
+		state.AtEndOfStream = false
+		return mlrval.FromBool(true)
+	}
+	state.Inrec = nil
+	state.Context = context
+	state.AtEndOfStream = true
+	return mlrval.FromBool(false)
+}
+
 func (root *RootNode) BuildBuiltinFunctionCallsiteNode(
 	astNode *dsl.ASTNode,
 ) (IEvaluable, error) {
@@ -29,6 +46,8 @@ func (root *RootNode) BuildBuiltinFunctionCallsiteNode(
 	if builtinFunctionInfo != nil {
 		if builtinFunctionInfo.hasMultipleArities { // E.g. "+" and "-"
 			return root.BuildMultipleArityFunctionCallsiteNode(astNode, builtinFunctionInfo)
+		} else if builtinFunctionInfo.zaryFuncWithState != nil {
+			return BuildZaryFunctionWithStateCallsiteNode(astNode, builtinFunctionInfo)
 		} else if builtinFunctionInfo.zaryFunc != nil {
 			return BuildZaryFunctionCallsiteNode(astNode, builtinFunctionInfo)
 		} else if builtinFunctionInfo.unaryFunc != nil {
@@ -105,6 +124,37 @@ func BuildZaryFunctionCallsiteNode(
 	}, nil
 }
 
+func BuildZaryFunctionWithStateCallsiteNode(
+	astNode *dsl.ASTNode,
+	builtinFunctionInfo *BuiltinFunctionInfo,
+) (IEvaluable, error) {
+	callsiteArity := len(astNode.Children)
+	expectedArity := 0
+	if callsiteArity != expectedArity {
+		return nil, fmt.Errorf(
+			"function %s invoked with %d argument%s; expected %d",
+			builtinFunctionInfo.name,
+			callsiteArity,
+			lib.Plural(callsiteArity),
+			expectedArity,
+		)
+	}
+
+	return &ZaryFunctionWithStateCallsiteNode{
+		zaryFuncWithState: builtinFunctionInfo.zaryFuncWithState,
+	}, nil
+}
+
+type ZaryFunctionWithStateCallsiteNode struct {
+	zaryFuncWithState ZaryFuncWithState
+}
+
+func (node *ZaryFunctionWithStateCallsiteNode) Evaluate(
+	state *runtime.State,
+) *mlrval.Mlrval {
+	return node.zaryFuncWithState(state)
+}
+
 func (node *ZaryFunctionCallsiteNode) Evaluate(
 	state *runtime.State,
 ) *mlrval.Mlrval {

pkg/dsl/cst/hofs.go

@@ -29,6 +29,9 @@ type BinaryFuncWithState func(
 	state *runtime.State,
 ) *mlrval.Mlrval
 
+// ZaryFuncWithState is for next() in mlr script.
+type ZaryFuncWithState func(state *runtime.State) *mlrval.Mlrval
+
 // TernaryFuncWithState is for fold.
 type TernaryFuncWithState func(
 	input1 *mlrval.Mlrval,

pkg/dsl/cst/leaves.go

@@ -122,6 +122,10 @@ func (node *FullSrecRvalueNode) Evaluate(
 	// print inrec attributes. Also, a UDF/UDS invoked from begin/end could try
 	// to access the inrec, and that would get past the validator.
 	if state.Inrec == nil {
+		// In mlr script, after next() returns false, $* is boolean false.
+		if state.AtEndOfStream {
+			return mlrval.FromBool(false)
+		}
 		return mlrval.ABSENT.StrictModeCheck(state.StrictMode, "$*")
 	}
 	return mlrval.FromMap(state.Inrec)

pkg/dsl/cst/types.go

@@ -28,6 +28,7 @@ const (
 	DSLInstanceTypePut = iota
 	DSLInstanceTypeFilter
 	DSLInstanceTypeREPL
+	DSLInstanceTypeScript
 )
 
 // Please see root.go for context and comments.

pkg/dsl/cst/validate.go

@@ -298,15 +298,15 @@ func validateForLoopMultivariableUniqueNames(astNode *dsl.ASTNode) error {
 }
 
 var VALID_LHS_NODE_TYPES = map[dsl.TNodeType]bool{
-	dsl.NodeTypeArrayOrMapIndexAccess:  true,
-	dsl.NodeTypeDotOperator:            true,
+	dsl.NodeTypeArrayOrMapIndexAccess: true,
+	dsl.NodeTypeDotOperator:           true,
 	dsl.NodeTypeArraySliceAccess:      true,
-	dsl.NodeTypeDirectFieldValue:       true,
-	dsl.NodeTypeDirectOosvarValue:      true,
-	dsl.NodeTypeEnvironmentVariable:    true,
-	dsl.NodeTypeFullOosvar:             true,
-	dsl.NodeTypeFullSrec:               true,
-	dsl.NodeTypeIndirectFieldValue:     true, // includes $[[n]] and $[[[n]]]
-	dsl.NodeTypeIndirectOosvarValue:    true,
-	dsl.NodeTypeLocalVariable:          true,
+	dsl.NodeTypeDirectFieldValue:      true,
+	dsl.NodeTypeDirectOosvarValue:     true,
+	dsl.NodeTypeEnvironmentVariable:   true,
+	dsl.NodeTypeFullOosvar:            true,
+	dsl.NodeTypeFullSrec:              true,
+	dsl.NodeTypeIndirectFieldValue:    true, // includes $[[n]] and $[[[n]]]
+	dsl.NodeTypeIndirectOosvarValue:   true,
+	dsl.NodeTypeLocalVariable:         true,
 }

pkg/runtime/state.go

@@ -43,6 +43,13 @@ type State struct {
 	// NoExitOnFunctionNotFound is used by the REPL: when true, a call to an
 	// undefined function returns an error mlrval instead of exiting the process.
 	NoExitOnFunctionNotFound bool
+
+	// NextRecordFunc is set by mlr script. When called, reads next record from input.
+	// Returns (record, context, hasMore). When hasMore is false, record and context are for end-of-stream.
+	NextRecordFunc func() (*mlrval.Mlrmap, *types.Context, bool)
+
+	// AtEndOfStream is set when next() returns false. Makes $* evaluate to boolean false.
+	AtEndOfStream bool
 }
 
 func NewEmptyState(options *cli.TOptions, strictMode bool) *State {

pkg/terminals/script/doc.go

@@ -0,0 +1,3 @@
+// Package script provides the mlr script terminal: non-interactive execution
+// of Miller DSL scripts with next()-driven record iteration.
+package script

pkg/terminals/script/entry.go

@@ -0,0 +1,153 @@
+// Entry point for mlr script: executes a Miller DSL script with next()-driven
+// record iteration. No prompt, no REPL. Script from -f or -e, data from
+// filenames or stdin.
+//
+// Example:
+//
+//	mlr script -f sum.mlr data.csv
+//	mlr script -e '@sum=0; while(next()){@sum+=$x}; print @sum' --csv data.csv
+
+package script
+
+import (
+	"fmt"
+	"os"
+	"path"
+	"strings"
+
+	"github.com/johnkerl/miller/v6/pkg/cli"
+	"github.com/johnkerl/miller/v6/pkg/lib"
+)
+
+func scriptUsage(verbName string, o *os.File, exitCode int) {
+	exeName := path.Base(os.Args[0])
+	fmt.Fprintf(o, "Usage: %s %s [options] -f {script file} | -e {expression} [zero or more data-file names]\n", exeName, verbName)
+	fmt.Fprint(o,
+		`-f {file}       Load DSL script from file. If file is a directory, load all *.mlr files.
+-e {expression}  DSL script from command line. May be combined with -f.
+
+--load {file}    Preload DSL before script (e.g. function library).
+--mload {files}  Like --load but multiple files. Use -- to terminate list.
+
+-w              Show warnings about uninitialized variables.
+-z              Strict mode.
+
+-h|--help       Show this message.
+
+Or any --icsv, --ojson, etc. reader/writer options.
+
+Data-file names (or stdin if none) are the record input stream.
+`)
+	os.Exit(exitCode)
+}
+
+func ScriptMain(args []string) int {
+	scriptName := args[0]
+	argc := len(args)
+	argi := 1
+
+	doWarnings := false
+	strictMode := false
+	options := cli.DefaultOptions()
+	var dslStrings []string
+	haveDSLStrings := false
+
+	for argi < argc {
+		if !strings.HasPrefix(args[argi], "-") {
+			break
+		}
+
+		if args[argi] == "-h" || args[argi] == "--help" {
+			scriptUsage(scriptName, os.Stdout, 0)
+		} else if args[argi] == "-w" {
+			doWarnings = true
+			argi++
+		} else if args[argi] == "-z" {
+			strictMode = true
+			argi++
+		} else if args[argi] == "-f" {
+			if argc-argi < 2 {
+				scriptUsage(scriptName, os.Stderr, 1)
+			}
+			argi++
+			filename, err := cli.VerbGetStringArg("script", "-f", args, &argi, argc)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "mlr: %v\n", err)
+				os.Exit(1)
+			}
+			theseStrings, err := lib.LoadStringsFromFileOrDir(filename, ".mlr")
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "mlr script: cannot load script from \"%s\": %v\n", filename, err)
+				os.Exit(1)
+			}
+			dslStrings = append(dslStrings, theseStrings...)
+			haveDSLStrings = true
+		} else if args[argi] == "-e" {
+			if argc-argi < 2 {
+				scriptUsage(scriptName, os.Stderr, 1)
+			}
+			argi++
+			expr, err := cli.VerbGetStringArg("script", "-e", args, &argi, argc)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "mlr: %v\n", err)
+				os.Exit(1)
+			}
+			dslStrings = append(dslStrings, expr)
+			haveDSLStrings = true
+		} else if args[argi] == "--load" {
+			if argc-argi < 2 {
+				scriptUsage(scriptName, os.Stderr, 1)
+			}
+			options.DSLPreloadFileNames = append(options.DSLPreloadFileNames, args[argi+1])
+			argi += 2
+		} else if args[argi] == "--mload" {
+			if argc-argi < 2 {
+				scriptUsage(scriptName, os.Stderr, 1)
+			}
+			argi++
+			for argi < argc && args[argi] != "--" {
+				options.DSLPreloadFileNames = append(options.DSLPreloadFileNames, args[argi])
+				argi++
+			}
+			if argi < argc && args[argi] == "--" {
+				argi++
+			}
+		} else if cli.FLAG_TABLE.Parse(args, argc, &argi, options) {
+		} else {
+			scriptUsage(scriptName, os.Stderr, 1)
+		}
+	}
+
+	if !haveDSLStrings {
+		fmt.Fprintf(os.Stderr, "mlr script: -f or -e is required\n")
+		scriptUsage(scriptName, os.Stderr, 1)
+	}
+
+	cli.FinalizeReaderOptions(&options.ReaderOptions)
+	cli.FinalizeWriterOptions(&options.WriterOptions)
+	options.WriterOptions.AutoFlatten = cli.DecideFinalFlatten(&options.WriterOptions)
+	options.WriterOptions.AutoUnflatten = cli.DecideFinalUnflatten(options, [][]string{})
+
+	filenames := args[argi:]
+
+	scr, err := NewScript(options, doWarnings, strictMode, dslStrings)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "mlr script: %v\n", err)
+		os.Exit(1)
+	}
+
+	scr.openFiles(filenames)
+	err = scr.run()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "mlr script: %v\n", err)
+		os.Exit(1)
+	}
+
+	scr.bufferedRecordOutputStream.Flush()
+	err = scr.closeBufferedOutputStream()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "mlr script: %v\n", err)
+		os.Exit(1)
+	}
+	return 0
+}

pkg/terminals/script/runner.go

@@ -0,0 +1,169 @@
+package script
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+
+	"github.com/johnkerl/miller/v6/pkg/cli"
+	"github.com/johnkerl/miller/v6/pkg/dsl/cst"
+	"github.com/johnkerl/miller/v6/pkg/input"
+	"github.com/johnkerl/miller/v6/pkg/lib"
+	"github.com/johnkerl/miller/v6/pkg/mlrval"
+	"github.com/johnkerl/miller/v6/pkg/output"
+	"github.com/johnkerl/miller/v6/pkg/runtime"
+	"github.com/johnkerl/miller/v6/pkg/types"
+)
+
+func NewScript(
+	options *cli.TOptions,
+	doWarnings bool,
+	strictMode bool,
+	dslStrings []string,
+) (*Script, error) {
+	recordReader, err := input.Create(&options.ReaderOptions, 1)
+	if err != nil {
+		return nil, err
+	}
+
+	recordWriter, err := output.Create(&options.WriterOptions)
+	if err != nil {
+		return nil, err
+	}
+
+	context := types.NewContext()
+	runtimeState := runtime.NewEmptyState(options, strictMode)
+	runtimeState.NoExitOnFunctionNotFound = true
+	runtimeState.Update(nil, context)
+	runtimeState.FilterExpression = mlrval.NULL
+
+	cstRootNode := cst.NewEmptyRoot(
+		&options.WriterOptions, cst.DSLInstanceTypeScript,
+	).WithRedefinableUDFUDS().WithStrictMode(strictMode)
+
+	// Collect all DSL: preloads first, then main script
+	allDSLStrings := []string{}
+	for _, filename := range options.DSLPreloadFileNames {
+		theseStrings, err := lib.LoadStringsFromFileOrDir(filename, ".mlr")
+		if err != nil {
+			return nil, fmt.Errorf("cannot load from \"%s\": %w", filename, err)
+		}
+		allDSLStrings = append(allDSLStrings, theseStrings...)
+	}
+	allDSLStrings = append(allDSLStrings, dslStrings...)
+
+	scr := &Script{
+		name:         "script",
+		doWarnings:   doWarnings,
+		cstRootNode:  cstRootNode,
+		options:      options,
+		recordReader: recordReader,
+		recordWriter: recordWriter,
+		runtimeState: runtimeState,
+	}
+
+	scr.recordOutputFileName = "(stdout)"
+	scr.recordOutputStream = os.Stdout
+	scr.bufferedRecordOutputStream = bufio.NewWriter(os.Stdout)
+
+	_, err = cstRootNode.Build(
+		allDSLStrings,
+		cst.DSLInstanceTypeScript,
+		false,
+		doWarnings,
+		nil,
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	return scr, nil
+}
+
+func (scr *Script) openFiles(filenames []string) {
+	scr.options.FileNames = filenames
+	scr.readerChannel = make(chan []*types.RecordAndContext, 2)
+	scr.errorChannel = make(chan error, 1)
+	scr.downstreamDoneChannel = make(chan bool, 1)
+
+	go scr.recordReader.Read(
+		filenames,
+		*scr.runtimeState.Context,
+		scr.readerChannel,
+		scr.errorChannel,
+		scr.downstreamDoneChannel,
+	)
+}
+
+func (scr *Script) run() error {
+	// Wire NextRecordFunc before running
+	readerChannel := scr.readerChannel
+	errorChannel := scr.errorChannel
+	bufferedOutput := scr.bufferedRecordOutputStream
+
+	scr.runtimeState.NextRecordFunc = func() (*mlrval.Mlrmap, *types.Context, bool) {
+		for {
+			var recordsAndContexts []*types.RecordAndContext
+			var err error
+			select {
+			case recordsAndContexts = <-readerChannel:
+			case err = <-errorChannel:
+			}
+
+			if err != nil {
+				return nil, scr.runtimeState.Context, false
+			}
+
+			if recordsAndContexts == nil {
+				return nil, scr.runtimeState.Context, false
+			}
+
+			lib.InternalCodingErrorIf(len(recordsAndContexts) != 1)
+			rac := recordsAndContexts[0]
+
+			if rac.EndOfStream {
+				return nil, &rac.Context, false
+			}
+
+			if rac.Record == nil {
+				// Output string from print/dump etc
+				bufferedOutput.WriteString(rac.OutputString)
+				bufferedOutput.Flush()
+				continue
+			}
+
+			// Actual record
+			return rac.Record, &rac.Context, true
+		}
+	}
+
+	// Execute begin blocks
+	err := scr.cstRootNode.ExecuteBeginBlocks(scr.runtimeState)
+	if err != nil {
+		return err
+	}
+
+	// Execute main block (script drives itself via next())
+	_, err = scr.cstRootNode.ExecuteMainBlock(scr.runtimeState)
+	if err != nil {
+		return err
+	}
+
+	// Execute end blocks
+	err = scr.cstRootNode.ExecuteEndBlocks(scr.runtimeState)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (scr *Script) closeBufferedOutputStream() error {
+	if scr.recordOutputStream != os.Stdout {
+		err := scr.recordOutputStream.Close()
+		if err != nil {
+			return fmt.Errorf("error on close: %w", err)
+		}
+	}
+	return nil
+}

pkg/terminals/script/types.go

@@ -0,0 +1,37 @@
+// Data types for the Miller script terminal.
+
+package script
+
+import (
+	"bufio"
+	"os"
+
+	"github.com/johnkerl/miller/v6/pkg/cli"
+	"github.com/johnkerl/miller/v6/pkg/dsl/cst"
+	"github.com/johnkerl/miller/v6/pkg/input"
+	"github.com/johnkerl/miller/v6/pkg/output"
+	"github.com/johnkerl/miller/v6/pkg/runtime"
+	"github.com/johnkerl/miller/v6/pkg/types"
+)
+
+type Script struct {
+	exeName string
+	name    string
+
+	doWarnings  bool
+	cstRootNode *cst.RootNode
+
+	options *cli.TOptions
+
+	readerChannel         chan []*types.RecordAndContext
+	errorChannel          chan error
+	downstreamDoneChannel chan bool
+	recordReader          input.IRecordReader
+	recordWriter          output.IRecordWriter
+
+	recordOutputFileName       string
+	recordOutputStream         *os.File
+	bufferedRecordOutputStream *bufio.Writer
+
+	runtimeState *runtime.State
+}

pkg/terminals/terminals.go

@@ -11,6 +11,7 @@ import (
 	"github.com/johnkerl/miller/v6/pkg/terminals/help"
 	"github.com/johnkerl/miller/v6/pkg/terminals/regtest"
 	"github.com/johnkerl/miller/v6/pkg/terminals/repl"
+	"github.com/johnkerl/miller/v6/pkg/terminals/script"
 	"github.com/johnkerl/miller/v6/pkg/version"
 )
 
@@ -34,6 +35,7 @@ func init() {
 		{"help", help.HelpMain},
 		{"regtest", regtest.RegTestMain},
 		{"repl", repl.ReplMain},
+		{"script", script.ScriptMain},
 		{"version", showVersion},
 	}
 }

test/cases/script/0001/cmd

@@ -0,0 +1 @@
+mlr script --csv -e '@sum=0; while(next()){@sum+=$x}; print @sum' ./${CASEDIR}/input

test/cases/script/0001/expout

@@ -0,0 +1 @@
+60

test/cases/script/0001/input

@@ -0,0 +1,4 @@
+a,b,x
+1,2,10
+3,4,20
+5,6,30