为什么`ls -l` 计数的文件比我多？

Question

显然我数不过来。我认为有三个文件/media

$ tree /media
/media
??? foo
??? onex
??? zanna
3 directories, 0 files

然而，ls -l发现 12。

$ ls -l /media
total 12
drwxr-xr-x  2 root root 4096 Jul 31 20:57 foo
drwxrwxr-x  2 root root 4096 Jun 26 06:36 onex
drwxr-x---+ 2 root root 4096 Aug  7 21:17 zanna

而且，如果我这样做，ls -la我只会得到.并且..除了上述之外，但计数是total 20

解释是什么？

Answer 1

在12你看到的是不是文件的数量，但磁盘块的数量消耗。

来自info coreutils 'ls invocation'：

 For each directory that is listed, preface the files with a line
 `total BLOCKS', where BLOCKS is the total disk allocation for all
 files in that directory.  The block size currently defaults to 1024
 bytes, but this can be overridden (*note Block size::).  The
 BLOCKS computed counts each hard link separately; this is arguably
 a deficiency.

当您使用而不是因为您正在计算两个额外的目录时，总数从12到：和。您为每个（空）目录使用四个磁盘块，因此您的总数从 3 × 4 变为 5 × 4。（很可能，您为每个目录使用了一个4096 字节的磁盘块；如页面所示，实用程序不检查磁盘格式，但除非另有说明，否则假定块大小为。）20ls -lals -l...info1024

如果您只想获取文件数，您可以尝试类似

ls | wc -l

Answer 2

user4556274 已经回答了原因。我的回答仅用于提供有关如何正确计算文件的附加信息。

在 Unix 社区中，普遍的共识是解析 的输出ls是一个非常非常糟糕的主意，因为文件名可以包含控制字符或隐藏字符。例如，由于文件名中的换行符，我们ls | wc -l告诉我们ls（它确实有）的输出中有 5 行，但实际上目录中只有 4 个文件。

$> touch  FILE$'\n'NAME                                                       
$> ls                                                                         
file1.txt  file2.txt  file3.txt  FILE?NAME
$> ls | wc -l
5

方法#1：查找实用程序

The find command, which is typically used for working around parsing filenames, can help us here by printing the inode number. Be it a directory or a file, it only has one unique inode number. Thus, using -printf "%i\n" and excluding . via -not -name "." we can have an accurate count of the files. (Note the use of -maxdepth 1 to prevent recursive descending into subdirectories)

$> find  -maxdepth 1 -not -name "." -print                                    
./file2.txt
./file1.txt
./FILE?NAME
./file3.txt
$> find  -maxdepth 1 -not -name "." -printf "%i\n" | wc -l                    
4

Method #2 : globstar

Simple, quick, and mostly portable way:

$ set -- * 
$ echo $#
228

set command is used to set positional parameters of the shell ( the $<INTEGER> variables, as in echo $1 ). This is often used to work around /bin/sh limitation of lacking arrays. A version that performs extra checks can be found in Gille's answer over on Unix&Linux.

In shells that support arrays, such as bash, we can use

items=( dir/* )
echo ${#items[@]}

as proposed by steeldriver in the comments.

Similar trick to find method which used wc and globstar can be used with stat to count inode numbers per line:

$> LC_ALL=C stat ./* --printf "%i\n" | wc -l                                          
4

An alternative approach is to use a wildcard in for loop. (Note, this test uses a different directory to test whether this approach descends into subdirectories, which it does not - 16 is the verified number of items in my ~/bin )

$> count=0; for item in ~/bin/* ; do count=$(($count+1)) ; echo $count ; done | tail -n 1                                
16

Method #3: other languages/interpreters

Python can also deal with problematic filenames via printing the length of a list given my os.listdir() function (which is non-recursive, and will only list items in the directory given as argument).

$> python -c "import os ; print os.listdir('.')"                              
['file2.txt', 'file1.txt', 'FILE\nNAME', 'file3.txt']
$>  python -c "import os ; print(len(os.listdir('.')))"                    
4

See also

• What's the most resource efficient way to count how many files are in a directory?