support multiline external commands and check_multi config

Changes

@@ -1,6 +1,7 @@
 This file documents the revision history for the SNClient agent.
 
 1.00     Fri Oct 16 16:47:03 CEST 2026
+         - add backslash line continuation for configuration values, including external commands and check_multi
          - add check_multi: execute multiple subchecks and evaluate the overall result
          - check_dns: resend lost packets and use the timeout and attempts settings of the resolv.conf
          - fix remaining zombie processes after automatic updates

docs/checks/external_commands/_index.md

@@ -25,7 +25,7 @@ You can add your custom scripts to SNClient using either a concise or verbose fo
 **Concise Format**:
 
 ```ini
-[/settings/external scripts]
+[/settings/external scripts/scripts]
 my_check1 = check_custom.bat
 my_check2 = myscripts\check_custom.bat
 ```
@@ -34,16 +34,36 @@ my_check2 = myscripts\check_custom.bat
 
 ```ini
 [/settings/external scripts/scripts/my_check1]
-my_check1 = check_custom.bat
+command = check_custom.bat
 
 [/settings/external scripts/scripts/my_check2]
-my_check2 = myscripts\check_custom.bat
+command = myscripts\check_custom.bat
 ```
 
 Both formats achieve the same outcome by adding two new commands, `my_check1` and `my_check2`, which execute
 the `check_custom.bat` script. Usually you use the short format, but if you want to provide individual options
 to a command, the long format is the way to go.
 
+In the concise format, the key is the command name. In the verbose format, the last
+part of the section path is the command name and the `command` key specifies what
+to execute. Settings such as `timeout` and `allow arguments` can be set in that
+section to override the global external script settings for that command.
+
+### Multiline Commands
+
+Long commands can be split across lines using a space or tab followed by `\` at
+the end of each continued line. For example:
+
+```ini
+[/settings/external scripts/scripts]
+check_myscript = ${scripts}/myscript.sh \
+          --arg1 foo \
+          --arg2 bar
+```
+
+The lines are joined with a single space before the command is parsed.
+See [multiline values](../../configuration/#multiline-values) for the syntax rules.
+
 ### Handling Script Arguments
 
 You can manage script arguments in two ways: embedding them directly into the command or allowing for argument pass-through.

docs/configuration/_index.md

@@ -100,6 +100,30 @@ check_also_keep = "part 1" something else "part 2"
 check_wrong = "unclosed quotes
 ```
 
+### Multiline Values
+
+End a line with a space or tab followed by `\` to continue its value on the next
+line. The backslash and surrounding whitespace, including indentation on the next
+line, are replaced with a single space. This works for configuration values in
+all sections, including external commands and `check_multi` commands.
+
+For example, check the size of a backup folder:
+
+```ini
+[/settings/check/multi/backups]
+command[size] = check_files \
+          "path=/srv/backups" \
+          "warn=total_size > 10GiB"
+```
+
+A continuation must be followed immediately by a nonempty line. A blank or
+whitespace-only line, or the end of the file, causes an `unfinished line
+continuation` error. Windows paths such as `C:\scripts\` remain unchanged because
+the final backslash is not preceded by a space or tab.
+
+See [external commands](../checks/external_commands/#multiline-commands) for an
+external command example.
+
 ### Appending Values
 
 You may use the `+=` operator to append to existing values and write

pkg/snclient/check_multi_test.go

@@ -11,6 +11,26 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func TestCheckMultiLineContinuation(t *testing.T) {
+	config := `
+[/settings/check/multi/multiline]
+command[ok] = check_dummy \
+          0 \
+          'multiline ok'
+command[warning] = check_dummy \
+          1 \
+          'multiline warning'
+`
+	snc := StartTestAgent(t, config)
+	defer StopTestAgent(t, snc)
+
+	res := snc.RunCheck("check_multi", []string{"config=multiline"})
+	assert.Equal(t, CheckExitWarning, res.State)
+	assert.Contains(t, res.Output, "2 plugins checked: 1 ok, 1 warning, 0 critical, 0 unknown")
+	assert.Contains(t, res.Details, "[ok] multiline ok")
+	assert.Contains(t, res.Details, "[warning] multiline warning")
+}
+
 func TestCheckMultiInline(t *testing.T) {
 	config := `
 [/modules]

pkg/snclient/config.go

@@ -282,9 +282,9 @@ func (config *Config) ParseINI(configData, iniPath string, snc *Agent) error {
 		lines = lines[:len(lines)-1]
 	}
 
-	for x, line := range lines {
-		lineNr := x + 1
-		line = strings.TrimSpace(line)
+	for lineIndex := 0; lineIndex < len(lines); lineIndex++ {
+		lineNr := lineIndex + 1
+		line := strings.TrimSpace(lines[lineIndex])
 		if line == "" || line[0] == ';' || line[0] == '#' {
 			currentComments = append(currentComments, line)
 
@@ -337,6 +337,17 @@ func (config *Config) ParseINI(configData, iniPath string, snc *Agent) error {
 			continue
 		}
 		val[0] = strings.TrimSpace(val[0])
+
+		// Require whitespace before continuation to preserve trailing Windows path separators.
+		for strings.HasSuffix(val[1], " \\") || strings.HasSuffix(val[1], "\t\\") {
+			if lineIndex+1 == len(lines) || strings.TrimSpace(lines[lineIndex+1]) == "" {
+				parseErrors = append(parseErrors, fmt.Errorf("config error in %s:%d: unfinished line continuation", iniPath, lineNr))
+
+				break
+			}
+			lineIndex++
+			val[1] = strings.TrimSpace(strings.TrimSuffix(val[1], "\\")) + " " + strings.TrimSpace(lines[lineIndex])
+		}
 		val[1] = strings.TrimSpace(val[1])
 
 		// silently skip UNKNOWN values which were placeholder in nsclient

pkg/snclient/config_test.go

@@ -61,6 +61,57 @@ test4 += c
 	assert.Equalf(t, expData, cfg.Section("/test").data, "config parsed")
 }
 
+func TestConfigLineContinuation(t *testing.T) {
+	configText := `[/settings/external scripts/scripts]
+check_ext = snclient run check_dummy \
+          0 \
+          $ARGS$
+[/test]
+quoted = "hello \
+          world"
+path = C:\scripts\
+next = unchanged
+append = first
+append += \
+	second
+`
+	for _, newline := range []string{"\n", "\r\n"} {
+		t.Run(fmt.Sprintf("newline=%q", newline), func(t *testing.T) {
+			cfg := NewConfig(false)
+			err := cfg.ParseINI(strings.ReplaceAll(configText, "\n", newline), "testfile.ini", nil)
+			require.NoError(t, err)
+			command, _ := cfg.Section("/settings/external scripts/scripts").GetString("check_ext")
+			assert.Equal(t, "snclient run check_dummy 0 $ARGS$", command)
+			assert.Equal(t, ConfigData{
+				"quoted": "hello world",
+				"path":   `C:\scripts\`,
+				"next":   "unchanged",
+				"append": "firstsecond",
+			}, cfg.Section("/test").data)
+		})
+	}
+}
+
+func TestConfigLineContinuationErrors(t *testing.T) {
+	for _, test := range []struct {
+		name   string
+		config string
+		error  string
+	}{
+		{"unfinished", "[/test]\nkey = value \\", "testfile.ini:2: unfinished line continuation"},
+		{"blank line", "[/test]\nkey = value \\\n\nnext = value\n", "testfile.ini:2: unfinished line continuation"},
+		{"whitespace line", "[/test]\r\nkey = value \\\r\n \t\r\nnext = value\r\n", "testfile.ini:2: unfinished line continuation"},
+		{"trailing blank line", "[/test]\nkey = value \\\n\n", "testfile.ini:2: unfinished line continuation"},
+		{"line number", "[/test]\nkey = value \\\n more\nbad\n", "testfile.ini:4: found key without '='"},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			cfg := NewConfig(false)
+			err := cfg.ParseINI(test.config, "testfile.ini", nil)
+			require.ErrorContains(t, err, test.error)
+		})
+	}
+}
+
 func TestConfigErrorI(t *testing.T) {
 	configText := `
 [/test]