使用python实现ls命令（1）
打算用python写一个ls命令脚本，以练习python基础。这个文档就是记录该小项目的进展和学习心得。
ls是Linux下最常用的命令之一，可以列出目录内文件即子目录名，可以配合众多参数使用。为此专门查看了Linux下man手册（我用ceontos7做的测试，其他Linux应该一样。但Windows环境下会有差异，比如Windows隐藏文件的方式与Linux不一样）。可以跳转首篇 查看这个小项目。
ls功能
–20191107
要用python实现ls命令，那先要了解ls功能，尤其是各种参数。我打算先实现基本功能，然后在逐步添加参数功能。以下是我导出linux系统中ls命令的man手册。
LS(1) User Commands LS(1)
NAME
ls - list directory contents
SYNOPSIS
ls [OPTION]... [FILE]...
DESCRIPTION
List information about the FILEs (the current directory by default). Sort entries alphabetically if none of -cftuvSUX nor
--sort is specified.
Mandatory arguments to long options are mandatory for short options too.
-a, --all
do not ignore entries starting with .
-A, --almost-all
do not list implied . and ..
--author
with -l, print the author of each file
-b, --escape
print C-style escapes for nongraphic characters
--block-size=SIZE
scale sizes by SIZE before printing them; e.g., '--block-size=M' prints sizes in units of 1,048,576 bytes; see SIZE
format below
-B, --ignore-backups
do not list implied entries ending with ~
-c with -lt: sort by, and show, ctime (time of last modification of file status information); with -l: show ctime and
sort by name; otherwise: sort by ctime, newest first
-C list entries by columns
--color[=WHEN]
colorize the output; WHEN can be 'never', 'auto', or 'always' (the default); more info below
-d, --directory
list directories themselves, not their contents
-D, --dired
generate output designed for Emacs' dired mode
-f do not sort, enable -aU, disable -ls --color
-F, --classify
append indicator (one of */=>@|) to entries
--file-type
likewise, except do not append '*'
--format=WORD
across -x, commas -m, horizontal -x, long -l, single-column -1, verbose -l, vertical -C
--full-time
like -l --time-style=full-iso
-g like -l, but do not list owner
--group-directories-first
group directories before files;
can be augmented with a --sort option, but any use of --sort=none (-U) disables grouping
-G, --no-group
in a long listing, don't print group names
-h, --human-readable
with -l, print sizes in human readable format (e.g., 1K 234M 2G)
--si likewise, but use powers of 1000 not 1024
-H, --dereference-command-line
follow symbolic links listed on the command line
--dereference-command-line-symlink-to-dir
follow each command line symbolic link
that points to a directory
--hide=PATTERN
do not list implied entries matching shell PATTERN (overridden by -a or -A)
--indicator-style=WORD
append indicator with style WORD to entry names: none (default), slash (-p), file-type (--file-type), classify (-F)
-i, --inode
print the index number of each file
-I, --ignore=PATTERN
do not list implied entries matching shell PATTERN
-k, --kibibytes
default to 1024-byte blocks for disk usage
-l use a long listing format
-L, --dereference
when showing file information for a symbolic link, show information for the file the link references rather than
for the link itself
-m fill width with a comma separated list of entries
-n, --numeric-uid-gid
like -l, but list numeric user and group IDs
-N, --literal
print raw entry names (don't treat e.g. control characters specially)
-o like -l, but do not list group information
-p, --indicator-style=slash
append / indicator to directories
-q, --hide-control-chars
print ? instead of nongraphic characters
--show-control-chars
show nongraphic characters as-is (the default, unless program is 'ls' and output is a terminal)
-Q, --quote-name
enclose entry names in double quotes
--quoting-style=WORD
use quoting style WORD for entry names: literal, locale, shell, shell-always, c, escape
-r, --reverse
reverse order while sorting
-R, --recursive
list subdirectories recursively
-s, --size
print the allocated size of each file, in blocks
-S sort by file size
--sort=WORD
sort by WORD instead of name: none (-U), size (-S), time (-t), version (-v), extension (-X)
--time=WORD
with -l, show time as WORD instead of default modification time: atime or access or use (-u) ctime or status (-c);
also use specified time as sort key if --sort=time
--time-style=STYLE
with -l, show times using style STYLE: full-iso, long-iso, iso, locale, or +FORMAT; FORMAT is interpreted like in
'date'; if FORMAT is FORMAT1FORMAT2, then FORMAT1 applies to non-recent files and FORMAT2 to recent files;
if STYLE is prefixed with 'posix-', STYLE takes effect only outside the POSIX locale
-t sort by modification time, newest first
-T, --tabsize=COLS
assume tab stops at each COLS instead of 8
-u with -lt: sort by, and show, access time; with -l: show access time and sort by name; otherwise: sort by access
time
-U do not sort; list entries in directory order
-v natural sort of (version) numbers within text
-w, --width=COLS
assume screen width instead of current value
-x list entries by lines instead of by columns
-X sort alphabetically by entry extension
-1 list one file per line
SELinux options:
--lcontext
Display security context. Enable -l. Lines will probably be too wide for most displays.
-Z, --context
Display security context so it fits on most displays. Displays only mode, user, group, security context and file
name.
--scontext
Display only security context and file name.
--help display this help and exit
--version
output version information and exit
SIZE is an integer and optional unit (example: 10M is 10*1024*1024). Units are K, M, G, T, P, E, Z, Y (powers of 1024) or
KB, MB, ... (powers of 1000).
Using color to distinguish file types is disabled both by default and with --color=never. With --color=auto, ls emits
color codes only when standard output is connected to a terminal. The LS_COLORS environment variable can change the set‐
tings. Use the dircolors command to set it.
Exit status:
0 if OK,
1 if minor problems (e.g., cannot access subdirectory),
2 if serious trouble (e.g., cannot access command-line argument).
GNU coreutils online help: .
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.
SEE ALSO
The full documentation for ls is maintained as a Texinfo manual. If the info and ls programs are properly installed at
your site, the command
info coreutils 'ls invocation'
should give you access to the complete manual.
GNU coreutils 8.22 November 2016 LS(1)
基本功能
之前看材料知道python自带os库。试着写下如下脚本：
import os
doc=os.listdir()
#print(a)
for i in doc:
print(i)
os库的listdir方法返回的是list类型，所以如果直接print(a)的话打印的和ls结果形式不太一样，所以使用了for循环拆开列表。