后面也会持续更新，学到新东西会在其中补充。
建议按顺序食用，欢迎批评或者交流！
缺什么东西欢迎评论！我都会及时修改的！
在这里真的很感谢这位老师的教学视频让迷茫的我找到了很好的学习视频
会查看命令是非常重要的！
whatis
简短解释该命令是啥意思
[root@RockyLinux9 ~]#whatis rm
rm (1) - remove files or directories
rm (1p) - remove directory entries
刚装好系统帮助不存在
centos7 以后
mandb
cento6 之前
makewhatiswhatis cal == man -f cal[root@RockyLinux9 ~]#whatis cal
cal (1) - display a calendar
cal (1p) - print a calendar
help
内部命令：
- help command
- man bash
外部命令：
- --help 或 -h
格式说明：
- [] 表示可选项
- CAPS或<>表示变化的数据
- ...表示多个列表
- x|y|z 意思是x或y或z
- -abc 意思是-a -b -c
- {} 表示分组
[root@RockyLinux9 ~]#type help
help is a shell builtin
[root@RockyLinux9 ~]#help echo
echo: echo [-neE] [arg ...]
Write arguments to the standard output.
...[-neE]中的是可选的选项 [arg]中的是可选的参数 ...是多个参数
echo: echo [-neE] [arg ...][root@RockyLinux9 ~]#help history
If the HISTTIMEFORMAT variable is set and not nullhelp显示的不太全man显示的很全面
[root@RockyLinux9 ~]#help history
history: history [-c] [-d offset] [n] or history -anrw [filename] or history -ps arg [arg...]
Display or manipulate the history list.
Display the history list with line numbers, prefixing each modified
entry with a `*'. An argument of N lists only the last N entries.
Options:
-c clear the history list by deleting all of the entries
-d offset delete the history entry at position OFFSET. Negative
offsets count back from the end of the history list
-a append history lines from this session to the history file
-n read all history lines not already read from the history file
and append them to the history list
-r read the history file and append the contents to the history
list
-w write the current history to the history file
-p perform history expansion on each ARG and display the result
without storing it in the history list
-s append the ARGs to the history list as a single entry
If FILENAME is given, it is used as the history file. Otherwise,
if HISTFILE has a value, that is used, else ~/.bash_history.
If the HISTTIMEFORMAT variable is set and not null, its value is used
as a format string for strftime(3) to print the time stamp associated
with each displayed history entry. No time stamps are printed otherwise.
Exit Status:
Returns success unless an invalid option is given or an error occurs.
[root@RockyLinux9 ~]#echo $HISTSIZE
1000
HISTSIZE这个变量在help 命令下并没有显示
--help
[root@RockyLinux9 ~]#date --help
Usage: date [OPTION]... [+FORMAT]
or: date [-u|--utc|--universal] [MMDDhhmm[[CC]YY][.ss]]
Display the current time in the given FORMAT, or set the system date.
Mandatory arguments to long options are mandatory for short options too.
-d, --date=STRING display time described by STRING, not 'now'
-h
[root@RockyLinux9 ~]#cal -h
Usage:
cal [options] [[[day] month] year]
cal [options] <timestamp|monthname>
Display a calendar, or some part of it.
Without any arguments, display the current month.
Options:
-1, --one show only a single month (default)
有些命令可以-h 可以 --help
[root@RockyLinux9 ~]#date -h
date: invalid option -- 'h'
Try 'date --help' for more information.
[root@RockyLinux9 ~]#date --help
Usage: date [OPTION]... [+FORMAT]
or: date [-u|--utc|--universal] [MMDDhhmm[[CC]YY][.ss]]
Display the current time in the given FORMAT, or set the system date.
常用的是--help 不行再用-h
多选一
date [-u|--utc|--universal]-u|--utc|--universal 都是三个功能一样的选项选出其中一个
man
shell 里面什么都有
[root@RockyLinux9 ~]#man bash
HISTSIZE
The number of commands to remember in the command history (see HISTORY
below). If the value is 0, commands are not saved in the history list.
Numeric values less than zero result in every command being saved on the
history list (there is no limit). The shell sets the default value to
500 after reading any startup files.
HISTTIMEFORMAT
If this variable is set and not null, its value is used as a format
string for strftime(3) to print the time stamp associated with each his‐
tory entry displayed by the history builtin. If this variable is set,
time stamps are written to the history file so they may be preserved
across shell sessions. This uses the history co有5千多行
man 页面分组为不同“章节”，统称Linux手册
[root@RockyLinux9 ~]#man 1 man
运维比较关注的是1 4 5 8
1 普通用户使用的 8 管理员使用的
[root@RockyLinux9 ~]#whatis rm
rm (1) - remove files or directories
rm (1p) - remove directory entries
（1）表示所在的章节编号第一章
我们打开man帮助也就是打开文件 man1就是章节1
[root@RockyLinux9 ~]#whereis ls
ls: /usr/bin/ls /usr/share/man/man1/ls.1.gz /usr/share/man/man1p/ls.1p.gz
不写man + 章节号 默认是从小开始 这里的话就是passwd (1)
[root@RockyLinux9 ~]#whatis passwd
passwd (5) - password file
passwd (1ossl) - OpenSSL application commands
passwd (1) - update user's authentication tokens
[root@RockyLinux9 ~]#man passwd
[root@RockyLinux9 ~]#man 5 passwd
关于/etc/issue的文件解释
[root@RockyLinux9 ~]#whatis issue
issue (5) - prelogin message and identification file
[root@RockyLinux9 ~]#man issue
[root@RockyLinux9 ~]#man 8 agetty
参考着手册写一下文件
[root@RockyLinux9 ~]#vi /etc/issue
[root@RockyLinux9 ~]#cat /etc/issue
Time at \t
Terminal on \l
xiaowang
\S
Kernel \r on an \m
man -a
[root@RockyLinux9 ~]#man -a passwd
man -k
想做一件事但是不知道那个命令可以用man -k
[root@RockyLinux9 ~]#man -k passwd
chgpasswd (8) - update group passwords in batch mode
chpasswd (8) - update passwords in batch mode
...man -w
列出文件位置
[root@RockyLinux9 ~]#man -w ls
/usr/share/man/man1/ls.1.gz
[root@RockyLinux9 ~]#whereis ls
ls: /usr/bin/ls /usr/share/man/man1/ls.1.gz /usr/share/man/man1p/ls.1p.gz
[root@RockyLinux9 ~]#man -w 5 passwd
/usr/share/man/man5/passwd.5.gz
范例：
[root@RockyLinux9 ~]#man 7 ascii
[root@RockyLinux9 ~]#man 7 utf-8
info
[root@RockyLinux9 ~]#info ls
总结
所有命令都需要反复敲来实验来记忆，本人基本上是个人理解加参考其他大佬的肯定有很多问题欢迎指正，我会及时修改。
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