From: Gábor Németh <homar@riseup.net>
Date: Thu, 29 Aug 2024 06:59:23 +0000 (+0200)
Subject: Optionally execute a program after group change
X-Git-Tag: v2.42-start~213^2
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=3b7aeba581e4421f25b9a739c43eb5fe3bdb31be;p=thirdparty%2Futil-linux.git

Optionally execute a program after group change

We accept a `-c` command option or possible second argument which is then
invoked through the user's shell after the group change, as by the `sg`
utility. The default is still running the shell itself.
---

diff --git a/bash-completion/newgrp b/bash-completion/newgrp
index 1e39c0f42..c6d678b93 100644
--- a/bash-completion/newgrp
+++ b/bash-completion/newgrp
@@ -8,15 +8,23 @@ _newgrp_module()
 		'-h'|'--help'|'-V'|'--version')
 			return 0
 			;;
+		'-c'|'--command')
+			COMPREPLY=( $(compgen -c -- $cur) )
+			return 0
+			;;
 	esac
 	case $cur in
 		-*)
-			OPTS="--version --help"
+			OPTS="--version --help --command"
 			COMPREPLY=( $(compgen -W "${OPTS[*]}" -- $cur) )
 			return 0
 			;;
 	esac
-	COMPREPLY=( $(compgen -g -- $cur) )
+	if (( COMP_CWORD == 1 )) || [[ " ${COMP_WORDS[@]}" =~ " "-?-c ]]; then
+		COMPREPLY=( $(compgen -g -- $cur) )
+	else
+		COMPREPLY=( $(compgen -c -- $cur) )
+	fi
 	return 0
 }
 complete -F _newgrp_module newgrp
diff --git a/login-utils/newgrp.1.adoc b/login-utils/newgrp.1.adoc
index e9a90d3ea..521b73559 100644
--- a/login-utils/newgrp.1.adoc
+++ b/login-utils/newgrp.1.adoc
@@ -18,7 +18,9 @@ newgrp - log in to a new group
 
 == SYNOPSIS
 
-*newgrp* [_group_]
+*newgrp* [_group_ [_command_]]
+
+*newgrp* [*-c* _command_] [_group_]
 
 == DESCRIPTION
 
@@ -26,8 +28,13 @@ newgrp - log in to a new group
 
 If no group is specified, the GID is changed to the login GID.
 
+An optional command can be specified, which is invoked after group change instead of the user's shell.
+
 == OPTIONS
 
+*-c*, *--command*=__command__::
+Pass _command_ to the user's shell with the *-c* option.
+
 include::man-common/help-version.adoc[]
 
 == FILES
diff --git a/login-utils/newgrp.c b/login-utils/newgrp.c
index e71a9e134..b9b620ed7 100644
--- a/login-utils/newgrp.c
+++ b/login-utils/newgrp.c
@@ -172,10 +172,10 @@ static void __attribute__((__noreturn__)) usage(void)
 {
 	FILE *out = stdout;
 	fputs(USAGE_HEADER, out);
-	fprintf(out, _(" %s <group>\n"), program_invocation_short_name);
+	fprintf(out, _(" %s <group> [[-c] <command>]\n"), program_invocation_short_name);
 
 	fputs(USAGE_SEPARATOR, out);
-	fputs(_("Log in to a new group.\n"), out);
+	fputs(_("Log in to a new group; optionally executing a shell command.\n"), out);
 
 	fputs(USAGE_OPTIONS, out);
 	fprintf(out, USAGE_HELP_OPTIONS(16));
@@ -187,11 +187,12 @@ int main(int argc, char *argv[])
 {
 	struct passwd *pw_entry;
 	struct group *gr_entry;
-	char *shell;
+	char *shell, *command = NULL;
 	int ch;
 	static const struct option longopts[] = {
 		{"version", no_argument, NULL, 'V'},
 		{"help", no_argument, NULL, 'h'},
+		{"command", required_argument, NULL, 'c'},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -200,8 +201,11 @@ int main(int argc, char *argv[])
 	textdomain(PACKAGE);
 	close_stdout_atexit();
 
-	while ((ch = getopt_long(argc, argv, "Vh", longopts, NULL)) != -1)
+	while ((ch = getopt_long(argc, argv, "c:Vh", longopts, NULL)) != -1)
 		switch (ch) {
+		case 'c':
+			command = optarg;
+			break;
 		case 'V':
 			print_version(EXIT_SUCCESS);
 		case 'h':
@@ -213,12 +217,12 @@ int main(int argc, char *argv[])
 	if (!(pw_entry = getpwuid(getuid())))
 		err(EXIT_FAILURE, _("who are you?"));
 
-	if (argc < 2) {
+	if (argc <= optind) {
 		if (setgid(pw_entry->pw_gid) < 0)
 			err(EXIT_FAILURE, _("setgid failed"));
 	} else {
 		errno = 0;
-		if (!(gr_entry = getgrnam(argv[1]))) {
+		if (!(gr_entry = getgrnam(argv[optind++]))) {
 			if (errno)
 				err(EXIT_FAILURE, _("no such group"));
 			else
@@ -236,6 +240,8 @@ int main(int argc, char *argv[])
 	fflush(NULL);
 	shell = (pw_entry->pw_shell && *pw_entry->pw_shell ?
 				pw_entry->pw_shell : _PATH_BSHELL);
-	execl(shell, shell, (char *)NULL);
+	if (!command && optind < argc)
+		command = argv[optind];
+	execl(shell, shell, command ? "-c" : NULL, command, (char *)NULL);
 	errexec(shell);
 }