Learning The Shell 📒

ln file link

ln -s item link

graph LR
A[hard link]
B[file]
C[soft link]
D[inode]
E[inode]
F[data block]
G[data block]
A --> D
B --> D
C --> E
D --> F
E --> G
G --> B

[root@golinux /]# type yum
yum is /usr/bin/yum
[root@golinux /]# type type
type is a shell builtin
[root@golinux /]# type ll
ll is aliased to `ls -l --color=auto'

[root@golinux /]# which yum
/usr/bin/yum
[root@golinux /]# which type
/usr/bin/which: no type in (/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin)
[root@golinux /]# which ll
alias ll='ls -l --color=auto'
	/usr/bin/ls

[root@golinux /]# help cd
cd: cd [-L|[-P [-e]]] [dir]
    Change the shell working directory.

    Change the current directory to DIR.  The default DIR is the value of the
    HOME shell variable.

    The variable CDPATH defines the search path for the directory containing
    DIR.  Alternative directory names in CDPATH are separated by a colon (:).
    A null directory name is the same as the current directory.  If DIR begins
    with a slash (/), then CDPATH is not used.

    If the directory is not found, and the shell option `cdable_vars' is set,
    the word is assumed to be  a variable name.  If that variable has a value,
    its value is used for DIR.

    Options:
        -L	force symbolic links to be followed
        -P	use the physical directory structure without following symbolic
    	links
        -e	if the -P option is supplied, and the current working directory
    	cannot be determined successfully, exit with a non-zero status

    The default is to follow symbolic links, as if `-L' were specified.

    Exit Status:
    Returns 0 if the directory is changed, and if $PWD is set successfully when
    -P is used; non-zero otherwise.

[root@golinux /]# mkdir --help
Usage: mkdir [OPTION]... DIRECTORY...
Create the DIRECTORY(ies), if they do not already exist.

Mandatory arguments to long options are mandatory for short options too.
  -m, --mode=MODE   set file mode (as in chmod), not a=rwx - umask
  -p, --parents     no error if existing, make parent directories as needed
  -v, --verbose     print a message for each created directory
  -Z                   set SELinux security context of each created directory
                         to the default type
      --context[=CTX]  like -Z, or if CTX is specified then set the SELinux
                         or SMACK security context to CTX
      --help     display this help and exit
      --version  output version information and exit

GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
For complete documentation, run: info coreutils 'mkdir invocation'

[root@golinux ~]# apropos partition
addpart (8)          - simple wrapper around the "add partition" ioctl
cfdisk (8)           - display or manipulate disk partition table
delpart (8)          - simple wrapper around the "del partition" ioctl
fdisk (8)            - manipulate disk partition table
iostat (1)           - Report Central Processing Unit (CPU) statistics and input/output statistics for devices and partitions.
kpartx (8)           - Create device maps from partition tables
os-prober (1)        - Discover bootable partitions on the local system.
parted (8)           - a partition manipulation program
partprobe (8)        - inform the OS of partition table changes
partx (8)            - tell the Linux kernel about the presence and numbering of on-disk partitions
resizepart (8)       - simple wrapper around the "resize partition" ioctl
sfdisk (8)           - partition table manipulator for Linux
systemd-efi-boot-generator (8) - Generator for automatically mounting the EFI System Partition used by the current boot to /boot
systemd-gpt-auto-generator (8) - Generator for automatically discovering and mounting root, /home and /srv partitions, as well as discover...

[root@golinux ~]# whatis ls
ls (1)               - list directory contents
[root@golinux ~]# whatis yum
yum (8)              - Yellowdog Updater Modified
[root@golinux ~]# whatis type
type (1)             - bash built-in commands, see bash(1)

[root@golinux ~]# alias la='ls -la'
[root@golinux ~]# la
total 104
dr-xr-x---.  8 root root 4096 Aug 29 17:38 .
dr-xr-xr-x. 18 root root 4096 May 10 15:12 ..
-rw-------   1 root root 8694 Sep  4 16:22 .bash_history
-rw-r--r--.  1 root root   18 Dec 29  2013 .bash_logout
-rw-r--r--.  1 root root  176 Dec 29  2013 .bash_profile
-rw-r--r--.  1 root root  176 Sep  4 16:21 .bashrc
drwx------   3 root root 4096 Oct 15  2017 .cache
-rw-r--r--.  1 root root  100 Dec 29  2013 .cshrc
drwxr-xr-x   7 root root 4096 Dec 21  2018 .nvm
drwxr-xr-x   2 root root 4096 Oct 15  2017 .pip
drwxr-----   3 root root 4096 Dec 21  2018 .pki
-rw-r--r--   1 root root   64 Oct 15  2017 .pydistutils.cfg
-rw-------   1 root root   37 Feb 16  2019 .python_history
drwx------   2 root root 4096 Dec 20  2018 .ssh
-rw-r--r--.  1 root root  129 Dec 29  2013 .tcshrc
drwxr-xr-x   6 root root 4096 Aug 26 15:15 .vim
-rw-------   1 root root 5324 Aug 29 17:38 .viminfo
-rw-------   1 root root 5121 Aug 26 23:19 .viminfo.tmp

ls -l /usr/bin > ls-output.txt

[root@golinux playground]# ls -l /bin/usr > ls-output.txt
ls: cannot access /bin/usr: No such file or directory

ls -l /bin/usr 2> ls-error.txt

ls -l /bin/usr > ls-output.txt 2>&1
# 或者
ls -l /bin/usr &> ls-output.txt

ls -l /bin/usr 2> /dev/null

cat ls-output.txt

cat movie.mpeg.0* > movie.mpeg

[root@golinux playground]# cat
hello world
hello world

[root@izbp13gye2rcpn1at3vj69z playground]# cat > little.txt
this is a little.txt # 输入文件内容
[root@izbp13gye2rcpn1at3vj69z playground]# cat little.txt
this is a little.txt # 打印文件内容

[root@izbp13gye2rcpn1at3vj69z playground]# cat < little.txt
this is the little.txt

graph TD
A[前一个命令的标准输出]
B[前一个命令的标准输出]
class A one
class B two
A --管道运算符--> B

[root@golinux playground]# ll / | less

ls /bin /usr/bin/ | sort | less