Linux Basic Learning 2

File directory structure

• Files and directories are organized into an inverted tree structure
• File system starts at root,'/'
• File names are case sensitive
• Hidden files begin with'..
• Path is delimited by'/'

File Naming Specification

• File characters up to 255 characters
• The maximum number of file names, including paths, is 4095
• Color Representation
  • Blue File-->Directory

• Green File-->Executable File, Executable Program

• Red File-->Compressed or Package File

• Light Blue File --> Link File, mainly files built with ln command

• White Files-->General Files such as Text Files, Configuration Files, Source Files, etc.
• Flashing red: problems with linked files
• Yellow: for device files
• Gray Files-->Other Files
• All characters except slash and NULL can be used
• Case sensitive

File System Structure

• /boot boot boot file location, the kernel file, boot loader are in this directory
• /bin Commands available to all users
• /sbin Management Class Commands
• /lib Basic library file used by program at startup.so end
• /lib64 specially stores auxiliary library files on X86_64 system
• /etc Store Profile
• /home/USERNAME Ordinary User's Home Directory
• /root Administrator's Home Directory
• Mount Point for/media Portable Mobile Devices
• /mnt temporary file mount point
• /dev device files and special files
• Installation location for/opt third-party applications
• /tmp temporary file storage location
• /usr Store Installer
• /var stores frequently changing files, such as logs
• /proc holds virtual files related to kernel startup and processes
• /sys Output hardware-related files on the current system
• Data used by allowed services on/srv systems

Composition of linux applications

• Binary file
  • /bin
  • /sbin
  • /usr/bin
  • /usr/sbin
  • /usr/local/bin
  • /usr/local/sbin
• Library Files
  • /lib
  • /lib64
  • /usr/lib
  • /usr/lib64
  • /usr/local/lib
  • /usr/local/lib64
• configuration file
  • /etc
  • /etc/name
  • /usr/local/etc
• Help Files
  • /usr/share/man
  • /usr/share/doc
  • /usr/local/share/man
  • /usr/local/share/doc

Absolute and relative paths

• Absolute path
  • Start with root
  • Full file location
  • Can read any file or folder
• Relative Path
  • Do not start with root
  • Determine relative to current position
  • Can be short to represent a file or folder
  • Current directory
  • ..Parent directory

Directory name and base name

[root@localhost log]#basename /etc/sysconfig/network-scripts/ifcfg-ens33 
ifcfg-ens33
[root@localhost log]#basename /etc/sysconfig/network-scripts
network-scripts
[root@localhost log]#dirname /etc/sysconfig/network-scripts
/etc/sysconfig
[root@localhost log]#dirname /etc/sysconfig/network-scripts/ifcfg-ens33 
/etc/sysconfig/network-scripts

Switch directories

cd switch directory change directory

• Relative paths can be used
• Absolute paths are available

Switch to Home Directory

[root@localhost log]#cd 
[root@localhost ~]#

Switch to the last directory

[root@localhost ~]#cd /etc/sysconfig/network-scripts/
[root@localhost network-scripts]#cd -
/root
[root@localhost ~]#cd -
/etc/sysconfig/network-scripts

Show current working directory

pwd print working directory

[root@localhost network-scripts]#pwd
/etc/sysconfig/network-scripts
# View the real directory of the link
[root@localhost /]#cd lib
[root@localhost lib]#pwd -P
/usr/lib

List directories or files

ls list

Command format: Usage: ls [OPTION]... [FILE]...

ls -a Show all files
[root@root ~]# ls -a
.                .cshrc  file15  file3  .passwd.swo
..               file1   file16  file4  .tcshrc
anaconda-ks.cfg  file10  file17  file5  teaching_plan.zip

ls -l Show file list in long format
[root@root ~]# ls -l
total 8
-rw-------. 1 root root 1414 Aug 22  2019 anaconda-ks.cfg
-rw-r--r--. 1 root root    0 Mar  1 18:28 file1

-rw-r--r--.    1        root     root      0    Aug 22 17:21  10
//Permission Hard Drive References Owned by Master Group Size Access Time File Name

ls -R Display directories recursively
[root@root ~]# ls -R
.:
anaconda-ks.cfg  file12  file16  file2   file5  file9
file1            file13  file17  file20  file6  teaching_plan.zip

ls -d Show the catalog itself
[root@root ~]# ls -d
.

ls -1(Number1) File Branch Display
[root@root ~]# ls -1
anaconda-ks.cfg
file1
file10
file11
file12


ls -S Installation File Size Sorting
[root@root ~]# ls -S
teaching_plan.zip  file11  file15  file19  file4  file8

ls -r Reverse Display
[root@root ~]# ls -r
teaching_plan.zip  file6  file20  file17  file13  file1

ls -t Sort by time
[root@root ~]# ls -t
file18  file11  file15  file3  file7  teaching_plan.zip

ls -lh Show human readable ways
[root@root ~]# ls -1h
anaconda-ks.cfg
file1
file10
file11
file12
file13

ls -d */ Show folders in the current directory
l. Show only hidden files

Catalog type under linux

• -used to represent files
• d is used to represent a directory
• b Block Device
• c character device
• l Represents a symbolic link file
• s socket socket

View file status

  File: 'anaconda-ks.cfg'
  Size: 1747        Blocks: 8          IO Block: 4096   regular file
Device: fd00h/64768d    Inode: 33574992    Links: 1
Access: (0600/-rw-------)  Uid: (    0/    root)   Gid: (    0/    root)
Context: system_u:object_r:admin_home_t:s0
Access: 2019-08-22 12:09:03.288000381 +0900 # Access time
Modify: 2019-08-22 11:47:12.262947345 +0900 # Modification Time
Change: 2019-08-22 11:47:12.262947345 +0900 # Change time
atime Access time to view file content changes
mtime Modification time changes content
ctime Changing time metadata changes

touch

Create empty file and refresh time, refresh time if file exists, create file if file does not exist

-a Modify only atime and ctime

-m only modifies mtime and ctime

File wildcards

• *All
• What?Matches any single character
• ~Indicates the user's home directory
• One of [123]
• [^123] Reverse
• [0-9] denotes a number
• file[a-z] letter (pitted) missing Z
• file[A-Z] letter (pitted) missing a
• [: lower:] lower case letters
• [: upper:] uppercase letters
• [: alpha:] All letters a-zA-Z
• [: alnum:] Represents letters and numbers
• [: digit:] denotes a number

Create directory

mkdir Create Directory

• -p Recursive Creation
• -v Show Detailed Procedures

display directory tree

Installation: Yum install-y tree

tree Displays Catalog tree

[root@root ~]# tree
.
├── anaconda-ks.cfg
├── file1
├── file10
├── file11
├── file12
├── file13
├── file14
├── file15
├── file16
├── file17
├── file18
├── file19
├── file2
├── file20
├── file3
├── file4
├── file5
├── file6
├── file7
├── file8
├── file9
└── teaching_plan.zip

0 directories, 22 files

-d Display folders only

[root@root ~]# tree -d
.

0 directories

-L #Show only #Layers

[root@root ~]# tree -L 1
.
├── anaconda-ks.cfg
├── file1
├── file10
├── file11
├── file12
├── file13
├── file14
├── file15
├── file16
├── file17
├── file18
├── file19
├── file2
├── file20
├── file3
├── file4
├── file5
├── file6
├── file7
├── file8
├── file9
└── teaching_plan.zip

0 directories, 22 files

Delete Directory

rmdir can only delete non-empty directories

-p Remove empty parent directory recursively

-v Displays the deletion process

Rm-rf Delete non-empty directories

Copy files and folders

cp copy is an alias by default and the original command itself is not prompted to overwrite

Usage: cp [OPTION]... [-T] SOURCE DEST
  or:  cp [OPTION]... SOURCE... DIRECTORY
  or:  cp [OPTION]... -t DIRECTORY SOURCE... 
  -i Show prompt information
  -n Not Covered
  -r -R Recursive replication
  -d Copy only linked files, not source files
  -a File
  -v Show process
  -b Back up the original file
  --backup=number Backup files plus numbers
  -p Keep original attributes
 

• If the source file is a file
  • Target is file
    • If the target file does not exist, create a new target file and write the contents to it
    • If the target file exists, the original command is to overwrite it directly. It is recommended that -i be used to prompt the user
  • Target is a folder
    • Create a new file with the same name in the folder and write the contents to the new file
• If the source file is more than one file
  • Target must be a folder, the folder must exist, everything else will go wrong
• If the source file is a folder
  • The target file is a file: no
  • The target file must be a folder and the -r option must be used
  • If the destination file does not exist: create the destination folder directly and copy all the data from the source folder to the destination folder
  • If the target file exists:
    • Error if file
    • If it is a folder: create a folder with the same name in the destination folder and copy all the data to the new folder

Move, Rename

mv move

Usage: mv [OPTION]... [-T] SOURCE DEST
  or:  mv [OPTION]... SOURCE... DIRECTORY
  or:  mv [OPTION]... -t DIRECTORY SOURCE...
-i Tips
-f force
-b backups
--backup=number Add a number after the backup
-v Show process

delete

rm remove

Usage: rm [OPTION]... FILE...
-i Tips
-r -R recursively
-f Force Delete
rm -rf Use with caution
rm -rf /*
cd /
rm -rf *

link

• Soft Link

• A shortcut equivalent to windows
• Create command Ln-S source file target file
• You can make soft links to directories
• The path to another file or directory, the size being the character of the path's length
• No effect on disk references
• Can cross partition
• Source file changes, soft links change

• Source file deleted, soft link not accessible

• Hard Link

• The number of disk references changes
• Pointing to the same area on the hard disk
• The number of references to the disk increases with the number of hard links
• Directories cannot be hard-linked
• Cannot span partitions
• The source file changes, and the hard links change

• Hard links are accessible when the source file is deleted

View File Types

file

Input and output

• Standard input defaults to stdin 0 from the keyboard
• Standard Output Default Output to Terminal Window stdout 1
• Standard error output default output to terminal window stderr 2

I/O Redirection

>Overlay

• >Redirect standard output to file
• 2>Redirect error output to file
• &>Redirect all output to a file

Prohibit, Allow Overlay

• Prohibit overwriting set-C
• Allow overwriting set +C

>Append

> Append the standard output to the file

2 > > Append error output to file

&>> Append all outputs to the file

Save standard input separately from error input

[root@localhost ~]#ls f 45yuio > log.log 2> error.log
[root@localhost ~]#cat log.log 
f
[root@localhost ~]#cat error.log 
ls: cannot access 45yuio: No such file or directory

Merge all outputs

• &>Override redirection
• & >> Acceleration Orientation
• command > file 2>&1
• command >> file 2>&1
• (): Combine output from multiple files
• /dev/null black hole

Import stdin from a file

tr character substitution

-t truncation
-d delete
-s Compression, Weight Removal
-c Reverse
[root@localhost ~]#tr 'a-z' 'A-Z' < /etc/issue
\S
KERNEL \R ON AN \M
[root@localhost ~]#tr 'a-z' 'A-Z' 
qwertyy
QWERTYY
12345678
12345678
ASDFGHJ
ASDFGHJ
qwertyuio
QWERTYUIO
^C
[root@localhost ~]#tr ab 12
ab
12
abb
122
asdfghjkl
1sdfghjkl
^C
[root@localhost ~]#tr abc 12
ab
12
abc
122
abc
122
^C
[root@localhost ~]#tr ab 123
ab
12
abb
122
avc
1vc
qbc
q2c
abc
12c
[root@localhost ~]#tr -t abc 12
abc
12c
ab
12
[root@localhost ~]#tr -d abc
qwertyui
qwertyui
an^H^H
n

abc

artyibrtyuiocrtyuiop
rtyirtyuiortyuiop
^C
[root@localhost ~]#tr -d abc < /etc/issue
\S
Kernel \r on n \m

[root@localhost ~]#cat /etc/issue
\S
Kernel \r on an \m
[root@localhost ~]#tr -s a
abc
abc
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaabc
abc
^C
[root@localhost ~]#tr -sc a 
aasdaaaaaaa
aasdaaaaaaa
^[[A^H^H^C
[root@localhost ~]#tr -sc a 
aaaaaaaaabbbbbbbbbbbbbccccccccddddddddddd
aaaaaaaaabcd
[root@localhost ~]#tr -dc a
aaaaaaaaaaaabbbbbbbbbb
asdfghjkqwertyuiozxcvbnmxcvbnm,.
aaaaaaaaaaaaa
ctrl+d End
[root@localhost ~]#tr -dc "a\n"
asdfghjk
a
wertyujk;l'



asdfghj
a
[root@localhost test]#Tr-d a < issue > issue cannot be written to the source file after processing is complete. Write to a new file
[root@localhost test]#seq 1 10 > b
[root@localhost test]#cat b
1
2
3
4
5
6
7
8
9
10
[root@localhost test]#tr -d "\n" < b
12345678910[root@localhost test]#tr -d "\n" < b
[root@localhost test]#tr "\n" " " <b
1 2 3 4 5 6 7 8 9 10 [root@localhost test]#tr "\n" " " <b >c
[root@localhost test]#cat c
1 2 3 4 5 6 7 8 9 10 [root@localhost test]#tr " " "\n" <c
1
2
3
4
5
6
7
8
9
10

Send multiple lines to stdin

# First way
[root@localhost test]#cat > f1
qwert
wertyui
wertyui
wertyuiopasdfghjk
sdfghjkl
sdfyhjkl;sdfghjkl;xcvb

# Second way
[root@localhost test]#cat > f2 <<EOF
> qwerty
> qwertyu
> wertyui
> qwertyu
> EOF
EOF Not necessarily, as long as two are identical

The Conduit

Pipeline is represented by'|'

Command 1|Command 2|Command 3

• Use the output of command 1 as the output of Command 2 and Command 2 as the input of command 3
• By default, pipes can only transfer standard output
• If error output needs to be passed along, then |&
• Commonly used to combine multiple commands
• Some commands do not accept pipelines

[root@localhost test]#ls f1|tr 'a-z' 'A-Z'
F1
[root@localhost test]#ls f
ls: cannot access f: No such file or directory
[root@localhost test]#ls f|tr 'a-z' 'A-Z'
ls: cannot access f: No such file or directory
[root@localhost test]#ls f|&tr 'a-z' 'A-Z'
LS: CANNOT ACCESS F: NO SUCH FILE OR DIRECTORY
[root@localhost test]#echo file{1..20}|touch 
touch: missing file operand
Try 'touch --help' for more information.