ls 指令可以说是Linux下最常用的指令之一。它有许多的选项，其中有许多是很有用的，你能否了解呢？下面列出了 ls 指令的绝大多数选项。
一运用举例：
1.列出具体文件 #ls -al //这个最常用，可是往往又不彻底符合要求，
2.列出一切子目录的文件：#ls -R //上个指令仅仅列出了本目录下的一切目录和文件，可是目录下的文件不会循环的列出。
3.若是文件过多一屏看不完，怎么办？并且，关于想找到许多文件中的某个文件的姓名。
3.1分屏显现：#ls -l|more //能在当时屏退出，很有用，但不能一页一页翻屏
#ls -l|less //能用pgup，pgdw 翻页，但不能在当时方位退出
3.2横向输出竟能够多的显现文件姓名：#ls -m
-a 列出目录下的一切文件，包含以 . 最初的隐含文件。//常用
-m 横向输出文件名，并以“，”作分格符。
-c 输出文件的 i 节点的修正时刻，并以此排序。
-R 列出一切子目录下的文件。
-l 列出文件的具体信息。
-s 在每个文件名后输出该文件的巨细。
-k 以 k 字节的方式表明文件的巨细。
-i 输出文件的 i 节点的索引信息。
2.只显现目录：#ls -l |grep ^d 只显现非目录文件：#ls-l |grep ^[^d]
3.对输出文件进行各种排序；
3.1 依照字符序(default): #ls -l
3.2 依照修正时刻排序： #ls -t //近来修正在最上面
3.3 逆排序 ： #ls -r
3.4 按文件巨细排序 ：#ls -S //大文件的在上
3.5 依照文件扩展名（最终一个.后的字符）排序： #ls -X
3.6 按数字排序 ：#ls -lv
-t 以时刻排序。
-r 对目录反向排序
-f -U 对输出的文件不排序。
-X 以文件的扩展名(最终一个 . 后的字符)排序。
-S 以文件巨细排序。
-u 以文件前次被拜访的时刻排序。
-n 用数字的 UID,GID 替代称号。
-o 显现文件的除组信息外的具体信息。
-p -F 在每个文件名后附上一个字符以阐明该文件的类型，“*”表明可执行的一般
文件；“/”表明目录；“@”表明符号连接；“|”表明FIFOs；“=”表明套
接字(sockets)。
-q 用?替代不行输出的字符。
。
下面来看看busybox对ls命令的实现
流程比较简单
先看下ls_main
/*----------------------------------------------------------------------*/
int ls_main(int argc, char **argv)
{
struct dnode **dnd;
struct dnode **dnf;
struct dnode **dnp;
struct dnode *dn;
struct dnode *cur;
long opt;
int nfiles = 0;
int dnfiles;
int dndirs;
int oi;
int ac;
int i;
char **av;
#ifdef CONFIG_FEATURE_AUTOWIDTH
char *tabstops_str = NULL;
char *terminal_width_str = NULL;
#endif
#ifdef CONFIG_FEATURE_LS_COLOR
char *color_opt;
#endif
all_fmt = LIST_SHORT |
(ENABLE_FEATURE_LS_SORTFILES * (SORT_NAME | SORT_ORDER_FORWARD));
#ifdef CONFIG_FEATURE_AUTOWIDTH
/* Obtain the terminal width. */
get_terminal_width_height(STDOUT_FILENO, &terminal_width, NULL);
/* Go one less... */
terminal_width--;
#endif
#ifdef CONFIG_FEATURE_LS_COLOR
bb_applet_long_options = ls_color_opt;
#endif
/* process options */
#ifdef CONFIG_FEATURE_AUTOWIDTH
opt = bb_getopt_ulflags(argc, argv, ls_options, &tabstops_str, &terminal_width_str
#ifdef CONFIG_FEATURE_LS_COLOR
, &color_opt
#endif
);
if (tabstops_str) {
tabstops = atoi(tabstops_str);
}
if (terminal_width_str) {
terminal_width = atoi(terminal_width_str);
}
#else
opt = bb_getopt_ulflags(argc, argv, ls_options
#ifdef CONFIG_FEATURE_LS_COLOR
, &color_opt
#endif
);
#endif
for (i = 0; opt_flags[i] != (1U<<31); i++) {
if (opt & (1 << i)) {
unsigned int flags = opt_flags[i];
if (flags & LIST_MASK_TRIGGER) {
all_fmt &= ~LIST_MASK;
}
if (flags & STYLE_MASK_TRIGGER) {
all_fmt &= ~STYLE_MASK;
}
if (ENABLE_FEATURE_LS_SORTFILES && (flags & SORT_MASK_TRIGGER)) {
all_fmt &= ~SORT_MASK;
}
if (flags & DISP_MASK_TRIGGER) {
all_fmt &= ~DISP_MASK;
}
if (flags & TIME_MASK) {
all_fmt &= ~TIME_MASK;
}
if (flags & LIST_CONTEXT) {
all_fmt |= STYLE_SINGLE;
}
#ifdef CONFIG_FEATURE_HUMAN_READABLE
if (opt == 'l') {
all_fmt &= ~LS_DISP_HR;
}
#endif
all_fmt |= flags;
}
}
#ifdef CONFIG_FEATURE_LS_COLOR
{
/* find color bit value - last position for short getopt */
#if CONFIG_FEATURE_LS_COLOR_IS_DEFAULT
char *p;
if ((p = getenv ("LS_COLORS")) != NULL &&
(*p == '\0' || (strcmp(p, "none") == 0))) {
;
} else if (isatty(STDOUT_FILENO)) {
show_color = 1;
}
#endif
if((opt & (1 << i))) { /* next flag after short options */
if (color_opt == NULL || strcmp("always", color_opt) == 0)
show_color = 1;
else if (color_opt != NULL && strcmp("never", color_opt) == 0)
show_color = 0;
else if (color_opt != NULL && strcmp("auto", color_opt) == 0 && isatty(STDOUT_FILENO))
show_color = 1;
}
}
#endif
/* sort out which command line options take precedence */
#ifdef CONFIG_FEATURE_LS_RECURSIVE
if (all_fmt & DISP_NOLIST)
all_fmt &= ~DISP_RECURSIVE; /* no recurse if listing only dir */
#endif
if (ENABLE_FEATURE_LS_TIMESTAMPS && ENABLE_FEATURE_LS_SORTFILES) {
if (all_fmt & TIME_CHANGE)
all_fmt = (all_fmt & ~SORT_MASK) | SORT_CTIME;
if (all_fmt & TIME_ACCESS)
all_fmt = (all_fmt & ~SORT_MASK) | SORT_ATIME;
}
if ((all_fmt & STYLE_MASK) != STYLE_LONG) /* only for long list */
all_fmt &= ~(LIST_ID_NUMERIC|LIST_FULLTIME|LIST_ID_NAME|LIST_ID_NUMERIC);
#ifdef CONFIG_FEATURE_LS_USERNAME
if ((all_fmt & STYLE_MASK) == STYLE_LONG && (all_fmt & LIST_ID_NUMERIC))
all_fmt &= ~LIST_ID_NAME; /* don't list names if numeric uid */
#endif
/* choose a display format */
if (!(all_fmt & STYLE_MASK))
all_fmt |= (isatty(STDOUT_FILENO) ? STYLE_COLUMNS : STYLE_SINGLE);
/*
* when there are no cmd line args we have to supply a default "." arg.
* we will create a second argv array, "av" that will hold either
* our created "." arg, or the real cmd line args. The av array
* just holds the pointers- we don't move the date the pointers
* point to.
*/
ac = argc - optind; /* how many cmd line args are left */
if (ac < 1) {
static const char * const dotdir[] = { "." };
av = (char **) dotdir;
ac = 1;
} else {
av = argv + optind;
}
/* now, everything is in the av array */
if (ac > 1)
all_fmt |= DISP_DIRNAME; /* 2 or more items? label directories */
/* stuff the command line file names into an dnode array */
dn = NULL;
for (oi = 0; oi < ac; oi++) {
cur = my_stat(av[oi], av[oi]);
if (!cur)
continue;
cur->allocated = 0;
cur->next = dn;
dn = cur;
nfiles++;
}
/* now that we know how many files there are
** allocate memory for an array to hold dnode pointers
*/
dnp = dnalloc(nfiles);
for (i = 0, cur = dn; i < nfiles; i++) {
dnp[i] = cur; /* save pointer to node in array */
cur = cur->next;
}
if (all_fmt & DISP_NOLIST) {//仅显示指定目录信息,不显示子目录
if (ENABLE_FEATURE_LS_SORTFILES) dnsort(dnp, nfiles);
if (nfiles > 0)
showfiles(dnp, nfiles);
} else {
dnd = splitdnarray(dnp, nfiles, SPLIT_DIR);
dnf = splitdnarray(dnp, nfiles, SPLIT_FILE);
dndirs = countdirs(dnp, nfiles);
dnfiles = nfiles - dndirs;
if (dnfiles > 0) {
if (ENABLE_FEATURE_LS_SORTFILES) dnsort(dnf, dnfiles);
showfiles(dnf, dnfiles);
if (ENABLE_FEATURE_CLEAN_UP)
free(dnf);
}
if (dndirs > 0) {
if (ENABLE_FEATURE_LS_SORTFILES) dnsort(dnd, dndirs);
showdirs(dnd, dndirs, dnfiles == 0);
if (ENABLE_FEATURE_CLEAN_UP)
free(dnd);
}
}
if (ENABLE_FEATURE_CLEAN_UP)
dfree(dnp, nfiles);
return (status);
}
ls_main也是先对参数进行解析，然后看是否需要递归显示该目录下的所以字目录，我们这里看下只显示该目录下的文件，而不显示他们的字目录，调用showfiles
/*----------------------------------------------------------------------*/
static void showfiles(struct dnode **dn, int nfiles)
{
int i, ncols, nrows, row, nc;
int column = 0;
int nexttab = 0;
int column_width = 0; /* for STYLE_LONG and STYLE_SINGLE not used */
if (dn == NULL || nfiles < 1)
return;
if (all_fmt & STYLE_ONE_RECORD_FLAG) {//格式的一些判断
ncols = 1;
} else {
/* find the longest file name- use that as the column width */
for (i = 0; i < nfiles; i++) {
int len = strlen(dn[i]->name) +
#ifdef CONFIG_SELINUX
((all_fmt & LIST_CONTEXT) ? 33 : 0) +
#endif
((all_fmt & LIST_INO) ? 8 : 0) +
((all_fmt & LIST_BLOCKS) ? 5 : 0);
if (column_width < len)
column_width = len;
}
column_width += tabstops;
ncols = (int) (terminal_width / column_width);
}
if (ncols > 1) {
nrows = nfiles / ncols;
if ((nrows * ncols) < nfiles)
nrows++; /* round up fractionals */
} else {
nrows = nfiles;
ncols = 1;
}
for (row = 0; row < nrows; row++) {
for (nc = 0; nc < ncols; nc++) {
/* reach into the array based on the column and row */
i = (nc * nrows) + row; /* assume display by column */
if (all_fmt & DISP_ROWS)
i = (row * ncols) + nc; /* display across row */
if (i < nfiles) {
if (column > 0) {
nexttab -= column;
while (nexttab--) {
putchar(' ');
column++;
}
}
nexttab = column + column_width;
column += list_single(dn[i]);//显示一行信息
}
}
putchar('\n');
column = 0;
}
}
Showfiles先对显示中间的一些空格,TAB长度做一些判断，然后调用list_single显示一行信息。
/*----------------------------------------------------------------------*/
static int list_single(struct dnode *dn)
{
int i, column = 0;
#ifdef CONFIG_FEATURE_LS_USERNAME
char scratch[16];
#endif
#ifdef CONFIG_FEATURE_LS_TIMESTAMPS
char *filetime;
time_t ttime, age;
#endif
#if defined(CONFIG_FEATURE_LS_FILETYPES) || defined (CONFIG_FEATURE_LS_COLOR)
struct stat info;
char append;
#endif
if (dn->fullname == NULL)
return (0);
#ifdef CONFIG_FEATURE_LS_TIMESTAMPS
ttime = dn->dstat.st_mtime; /* the default time */
if (all_fmt & TIME_ACCESS)
ttime = dn->dstat.st_atime;
if (all_fmt & TIME_CHANGE)
ttime = dn->dstat.st_ctime;
filetime = ctime(&ttime);
#endif
#ifdef CONFIG_FEATURE_LS_FILETYPES
append = append_char(dn->dstat.st_mode);
#endif
for (i = 0; i <= 31; i++) {
switch (all_fmt & (1 << i)) {
case LIST_INO:
column += printf("%7ld ", (long int) dn->dstat.st_ino);
break;
case LIST_BLOCKS:
#if _FILE_OFFSET_BITS == 64
column += printf("%4lld ", (long long)dn->dstat.st_blocks >> 1);
#else
column += printf("%4ld ", dn->dstat.st_blocks >> 1);
#endif
break;
case LIST_MODEBITS:
column += printf("%-10s ", (char *) bb_mode_string(dn->dstat.st_mode));
break;
case LIST_NLINKS:
column += printf("%4ld ", (long) dn->dstat.st_nlink);
break;
case LIST_ID_NAME://显示用户名
#ifdef CONFIG_FEATURE_LS_USERNAME
bb_getpwuid(scratch, dn->dstat.st_uid, sizeof(scratch));
printf("%-8.8s ", scratch);
bb_getgrgid(scratch, dn->dstat.st_gid, sizeof(scratch));
printf("%-8.8s", scratch);
column += 17;
break;
#endif
case LIST_ID_NUMERIC:
column += printf("%-8d %-8d", dn->dstat.st_uid, dn->dstat.st_gid);
break;
case LIST_SIZE:
case LIST_DEV:
if (S_ISBLK(dn->dstat.st_mode) || S_ISCHR(dn->dstat.st_mode)) {
column += printf("%4d, %3d ", (int) major(dn->dstat.st_rdev),
(int) minor(dn->dstat.st_rdev));
} else {
#ifdef CONFIG_FEATURE_HUMAN_READABLE
if (all_fmt & LS_DISP_HR) {
column += printf("%9s ",
make_human_readable_str(dn->dstat.st_size, 1, 0));
} else
#endif
{
#if _FILE_OFFSET_BITS == 64
column += printf("%9lld ", (long long) dn->dstat.st_size);
#else
column += printf("%9ld ", dn->dstat.st_size);
#endif
}
}
break;
#ifdef CONFIG_FEATURE_LS_TIMESTAMPS
case LIST_FULLTIME:
printf("%24.24s ", filetime);
column += 25;
break;
case LIST_DATE_TIME:
if ((all_fmt & LIST_FULLTIME) == 0) {
age = time(NULL) - ttime;
printf("%6.6s ", filetime + 4);
if (age < 3600L * 24 * 365 / 2 && age > -15 * 60) {
/* hh:mm if less than 6 months old */
printf("%5.5s ", filetime + 11);
} else {
printf(" %4.4s ", filetime + 20);
}
column += 13;
}
break;
#endif
#ifdef CONFIG_SELINUX
case LIST_CONTEXT:
{
char context[80];
int len = 0;
if (dn->sid) {
/* I assume sid initilized with NULL */
len = strlen(dn->sid)+1;
safe_strncpy(context, dn->sid, len);
freecon(dn->sid);
}else {
safe_strncpy(context, "unknown", 8);
}
printf("%-32s ", context);
column += MAX(33, len);
}
break;
#endif
case LIST_FILENAME:
#ifdef CONFIG_FEATURE_LS_COLOR
errno = 0;
if (show_color && !lstat(dn->fullname, &info)) {
printf("\033[%d;%dm", bgcolor(info.st_mode),
fgcolor(info.st_mode));
}
#endif
column += printf("%s", dn->name);
#ifdef CONFIG_FEATURE_LS_COLOR
if (show_color) {
printf("\033[0m");
}
#endif
break;
case LIST_SYMLINK:
if (S_ISLNK(dn->dstat.st_mode)) {
char *lpath = xreadlink(dn->fullname);
if (lpath) {
printf(" -> ");
#if defined(CONFIG_FEATURE_LS_FILETYPES) || defined (CONFIG_FEATURE_LS_COLOR)
if (!stat(dn->fullname, &info)) {
append = append_char(info.st_mode);
}
#endif
#ifdef CONFIG_FEATURE_LS_COLOR
if (show_color) {
errno = 0;
printf("\033[%d;%dm", bgcolor(info.st_mode),
fgcolor(info.st_mode));
}
#endif
column += printf("%s", lpath) + 4;
#ifdef CONFIG_FEATURE_LS_COLOR
if (show_color) {
printf("\033[0m");
}
#endif
free(lpath);
}
}
break;
#ifdef CONFIG_FEATURE_LS_FILETYPES
case LIST_FILETYPE:
if (append != '\0') {
printf("%1c", append);
column++;
}
break;
#endif
}
}
return column;
}
list_single根据all_fmt值(即ls的参数)，显示相关的信息，这里主要看用户名是如何显示的。
这里linux和android的实现是不一样的，因为Android没有/etc/passwd、也就没有办法保存uid和他对应的name，而且在Android上面我们不需要使用adduser去为每个应用新建一个用户的，我们看一下Android里面的用户名是怎么来的。
这是获取用户名的流程，那getgrgid_r是在那实现的呢，没错，是bonic
在\bionic\libc\bionic\Stubs.cpp中
最终是通过print_app_name_from_appid_userid来获取用户名的
static void print_app_name_from_appid_userid(const uid_t appid,
const uid_t userid, char* buffer, const int bufferlen) {
__libc_android_log_print(ANDROID_LOG_ERROR, "leaves app_id_from_name", "leave appid = %d", appid);
if (appid >= AID_ISOLATED_START) {
snprintf(buffer, bufferlen, "u%u_i%u", userid, appid - AID_ISOLATED_START);
} else if (userid == 0 && appid >= AID_SHARED_GID_START) {
snprintf(buffer, bufferlen, "all_a%u", appid - AID_SHARED_GID_START);
} else if (appid < AID_APP) {//小于应用id的起始值
for (size_t n = 0; n < android_id_count; n++) {
if (android_ids[n].aid == appid) {
snprintf(buffer, bufferlen, "u%u_%s", userid, android_ids[n].name);
return;
}
}
} else {
snprintf(buffer, bufferlen, "u%u_a%u", userid, appid - AID_APP);//应用程序的uid name
}
__libc_android_log_print(ANDROID_LOG_ERROR, "leaves app_id_from_name", "leave buffer = %s", buffer);
}
从代码中可以看到，应用程序最终的name 都是u +uid + _ + a + appid –AID_APP
如下图：
Uid都是0
Linux下面的实现也是类似的，其getpwuid_r是在glic中实现的，这里就没去研究。