coreutils8.32 whoami命令和源码分析

命令功能：显示当前操作用户（不是登陆用户，和logname不一样。登陆用户之后可以su切换操作用户）

执行流程：先用geteuid获取调用进程的用户uid，再用getpwuid通过uid获取完整的passwd结构再输出用户名

/* whoami -- print effective useridCopyright (C) 1989-2020 Free Software Foundation, Inc.This program is free software: you can redistribute it and/or modifyit under the terms of the GNU General Public License as published bythe Free Software Foundation, either version 3 of the License, or(at your option) any later version.This program is distributed in the hope that it will be useful,but WITHOUT ANY WARRANTY; without even the implied warranty ofMERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See theGNU General Public License for more details.You should have received a copy of the GNU General Public Licensealong with this program.  If not, see <https://www.gnu.org/licenses/>.  *//* Equivalent to 'id -un'. */
/* Written by Richard Mlynarik. */#include <config.h>
#include <stdio.h>
#include <sys/types.h>
#include <pwd.h>#include "system.h"
#include "die.h"
#include "error.h"
#include "long-options.h"
#include "quote.h"/* The official name of this program (e.g., no 'g' prefix).  */
#define PROGRAM_NAME "whoami"#define AUTHORS proper_name ("Richard Mlynarik")void
usage (int status)
{if (status != EXIT_SUCCESS)emit_try_help ();else{printf (_("Usage: %s [OPTION]...\n"), program_name);fputs (_("\
Print the user name associated with the current effective user ID.\n\
Same as id -un.\n\
\n\
"), stdout);fputs (HELP_OPTION_DESCRIPTION, stdout);fputs (VERSION_OPTION_DESCRIPTION, stdout);emit_ancillary_info (PROGRAM_NAME);}exit (status);
}int
main (int argc, char **argv)
{struct passwd *pw;uid_t uid;uid_t NO_UID = -1;initialize_main (&argc, &argv);set_program_name (argv[0]);setlocale (LC_ALL, "");bindtextdomain (PACKAGE, LOCALEDIR);textdomain (PACKAGE);atexit (close_stdout);parse_gnu_standard_options_only (argc, argv, PROGRAM_NAME, PACKAGE_NAME, Version, true, usage, AUTHORS, (char const *) NULL);/* whoami不能传入选项和参数 */if (optind != argc){error (0, 0, _("extra operand %s"), quote (argv[optind]));usage (EXIT_FAILURE);}errno = 0;uid = geteuid ();  /* 获取当前调用进程的用户uid */pw = (uid == NO_UID && errno ? NULL : getpwuid (uid));  /* c语言写法：如果geteuid成功获取用户uid的话就调用getpwuid获取passwd文件下uid的完整用户信息 */if (!pw)  /* getpwuid获取失败 */die (EXIT_FAILURE, errno, _("cannot find name for user ID %lu"),(unsigned long int) uid);puts (pw->pw_name);  /* 输出用户名 */return EXIT_SUCCESS;
}

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