Linux basic Commands (ii)

Linux directory and file management 1.Linux directory structure

Linux is a reciprocal structure , from '/' as a starting point, where all files or directories are represented by '/'
Linux has only one '/', analogy to Windows has multiple '/' (a disk one '/')

Example :
such as the location of the Docs directory
/bin/mark/docsis equivalent to Windows (C:\bin\mark\docs)
Note : '/' as a starting point, the directory and files are separated by '/# '
Common Linux Directories :

• /etc///Store all configuration files
• /bin///Storing system commands that all users can execute
• /sbin///Store system commands that only administrators (root) or users with administrator privileges can perform
• /mnt///default is empty for temporary mount
• /var///Dynamic storage directory, storing dynamic files, such as logs, mail, etc.
• /dev///storage equipment, such as hard disk, CD-ROM, etc.
• /home///General user home Directory
• /root///admin Root home directory
• /usr///user self-installing software storage directory
• /boot///store kernel, boot file directory
  Note：all files under Linux, such as the keyboard, mouse and so on in the Linux are embodied as a file, but some files can not be opened directly, you need to use the program or software Call 2. View and retrieve file CD commands

  CD < directory path to enter >
  Switch the directory (equivalent to a mouse double-click into a directory in Windows, directly view the contents of the directory)
  Example :
  pwdView your current directory
  
  cd /etc/Switch from the current path to the/etc/directory
  
  cd 或 cd ~Enter the current login user home directory
  
  cd -Go to last switch directory
  
  Relative path and absolute path
  relative path : Represents the position starting from the current path;./For the current directory, ... /represents the upper-level path
  Absolute Path : The full representation of the path starting from "/"
  Example :
  ① represents the "/etc/sysconfig/network-scripts/ifcfg-eth0" file location, currently located in the "etc/" directory
  Relative path:./sysconfig/network-scripts/ifcfg-eth0 or Sysconfig/network-scripts/ifcfg-eth0
  Absolute path:/etc/sysconfig/network-scripts/ifcfg-eth0
  ② represents the "/etc/hosts" file location, currently located in the "/etc/sysconfig/network-scripts/" directory
  Relative path: /.. /hosts
  Absolute path/etc/hosts
  Note : Generally relatively more convenient than absolute use, can reduce the file structure, of course, according to the customary use can

  Cat command

  Cat [Options] File name:
  Display file contents to view multiple file contents at the same time
  Options :
  -N: Show line numbers
  -A: Displays all special symbols in the file, such as "$" terminator, etc.
  Example :
  cat /etc/hostsView/etc/hosts file contents
  
  cat -n /etc/hostsView/etc/hosts file contents and display line numbers
  
  cat -A /etc/hostsView the contents of the/etc/hosts file and all its special symbols
  

  More commands

  More [options] File name ...
  Full screen display of the contents of the file, can be paged to view multiple files at the same time
  shortcut keys :
  Enter key: Line down
  SPACEBAR: Turn down one page
  Q Key: Exit
  Example :
  more /root/anaconda-ks.cfgPaging View/root/anaconda-ks.cfg File
  
  
  Note : More can only be turned upside down, cannot go up

  Less command

  Less [options] file name ...
  Same as the more command, but supports scrolling up and down, and supports the search function
  shortcut keys :
  Page UP key: Page UP
  Page DOWN key: Page Down
  /text: Find specified file in file
  N: Jumps to the next address in the search text in the file
  N: Jump to the previous address in the file to search for files
  Q Key: Exit
  Example :
  less /root/anaconda-ks.cfg
  
  

  Detailed Head command

  Head-n file name ...
  View part of the beginning of a file (default is 10 lines)
  head /root/anaconda-ks.cfgView the beginning of the file 10 lines
  
  head -3 /root/anaconda-ks.cfgView the beginning of the file 3 lines
  

  Tail command

  Tail-n file name ...
  View a portion of the end of the file (default is 10 lines)
  Options :
  -F: Dynamic update To view the end of the file, real-time monitoring file changes (CTRL + C key termination), generally used for the log
  Example :
  tail /root/anaconda-ks.cfgView end of file 10 lines
  
  tail -3 /root/anaconda-ks.cfgView end of File 3 lines
  
  tail -f /var/log/messagesTo view the public message log file dynamically
  

  WC command

  WC [Options] File
  Information about the number of words in the statistics file (Word Count), file size, number of file lines, and more
  Options :
  -L: Count rows
  -W: Count the number of words, separated by spaces
  -C: Statistics of bytes
  Example :
  wc /etc/hostsThe situation of statistical/etc/hosts
  
  Note : When using the WC command, do not follow any options, default use WC-LWC
  wc -l /etc/hostsCount the number of lines in a/etc/hosts file
  
  wc -l /etc/passwdCount/etc/passwd file lines to get the number of accounts in the system
  
  find /etc -name "*.conf" | wc -lStatistics. conf number of files ending in
  

  grep command

  grep [Options] ... < find criteria > < destination file >
  Finds and displays the line containing the specified string in the file
  Options :
  -I: Ignore case when finding
  -V: Reverse lookup, output rows that do not match the condition
  Search Criteria :
  The searched string should be enclosed in double quotation marks ("").
  "^ ..." means ... The beginning, "... $" represents a ... End
  "^$" indicates a blank line
  Example :
  grep "f" /etc/inittabFilter the lines in the display file that contain F (match lowercase characters F only)
  
  grep -i "f" /etc/inittabFilter the lines in the display file that contain F (ignoring case, case f)
  
  grep "f$" /etc/inittabFilter the lines that end with F in the display file
  
  grep "^i" /etc/inittabFilter the lines that start with I in the display file
  
  grep -v "^#" /etc/inittabFilter the remaining lines in the display file except #
  
  grep -v "^$" /etc/inittabTo filter the remaining lines in the file that are empty lines apart
  
  grep -v "^#" /etc/inittab | grep -v "^$"Display valid lines in a file (no blank lines and # start lines are displayed)
  

• 3. File compression and archiving gzip and gunzip

  gzip [-9] < filename ...//compression
  GZIP-D xx.gz Format compressed file or gunzip xx.gz format compressed file//Unzip
  Use the GZIP compression algorithm to compress files, unzip compressed files (can reduce file occupancy, but not absolute)
  Options :
  -9: High compression ratio, compressed files smaller (from 0~9, the larger the number, the higher the compression ratio, the default is 6)
  -D: For extracting files
  Example :
  dd if=/dev/zero of=/root/test bs=100M count=1Generate a test file of size 100M
  
  gzip /root/testUse gzip to compress the file, the original file is lost and changed to Test.gz
  
  gzip -d /root/test.gzUnzip the test.gz file to the original directory
  
  Note : Only files compressed using gzip can be decompressed, with the suffix. gz
  gzip -9 /root/testHigh compression ratio using gzip compressed files, default to 6
  
  gunzip /root/test.gzUnzip using the Gunzip command, as with the gzip-d effect
  

  Bzip2 and BUNZIP2

  bzip2 [-9] < filename ...//compression
  BZIP2-D xx.bz2 Format compressed file or BUNZIP2 xx.bz2 format compressed file//Unzip
  Use the BZIP2 compression algorithm to compress files, extract compressed files (can reduce file occupancy, but not absolute)
  Options :
  -9: High compression ratio, compressed files smaller (from 0~9, the larger the number, the higher the compression ratio, the default is 6)
  -D: For extracting files
  Example :
  bzip2 /root/testUse bzip2 to compress the file, the original file is lost and changed to TEST.BZ2
  
  bzip2 -d /root/test.bz2Unzip the test.bz2 file to the original directory
  
  Note : Only files compressed using the Bzip2 method can be decompressed, with the suffix. bz2
  bzip2 -9 /root/testHigh compression ratio using bzip2 compressed files, default to 6
  
  bunzip2 /root/test.bz2Unzip using the BUNZIP2 command, as with the bzip2-d effect
  

  Xz

  XZ [-9] < filename ...//compression
  xz-d compressed files//decompression in XX.XZ format
  Use the XZ compression algorithm to compress files, extract compressed files (can reduce file occupancy, but not absolute)
  Options :
  -9: High compression ratio, compressed files smaller (from 0~9, the larger the number, the higher the compression ratio, the default is 6)
  -D: For extracting files
  Example :
  xz /root/testUse XZ mode to compress the file, the original file is lost to Test.xz
  
  xz -d /root/test.xzUnzip the Test.xz file to the original directory
  
  Note : Only files compressed using XZ mode can be decompressed, with the suffix. XZ
  xz -9 /root/testHigh compression ratio using XZ compressed files, default to 6
  
  xz -d /root/test.xzUnzip the Test.xz file to the original directory
  
  Comparison of three compression modes

• gzip is best for files to be used under the Unix/linux system, although bzip2 is already popular, but Gzip will still be used for a long time
• bzip2 uses a different algorithm than gzip and produces smaller files than gzip, but takes longer to compress
• XZ provides the best compression rate, but it also takes a considerable amount of time. Newer than gzip, bzip2, but some systems may not be installed (self-installing)
• Summary: xz > Bzip2 > Gziptar

  tar [options] ... < archive file name > < source file or directory >//Create Archive
  tar [options] ... < archive file name > [-c < target directory;]//Unzip archive
  Options：
  -Z: Call the gzip program for compression or decompression
  -J: Call bzip2 Program for compression or decompression
  -j: Call the XZ program for compression or program
  -C: Create a package file in. tar format
  -X: Unpack the. tar format package file
  -T: List view in-package files
  -V: Output details
  -F: Using an archive file
  -P: Preserve the original file and directory permissions while packaging
  -C: Specify the target folder to release when unpacking
  -P: Archive with absolute path (resolves "tar:removing leading '/' from member names" issue)
  Note: With tar archive, source files or folders are not lost and still exist (Windows-like compression tools)
  Example：
  (1) Filing
  tar -zcvf /root/ceshi.tar.gz /boot/ /bin/Archive the/boot/and/bin/directories as a file using gzip and place them under/root/named ceshi.tar.gz
  
  tar -jcvf /root/ceshi.tar.bz2 /boot/ /bin/Archive the/boot/and/bin/directories as a file using bzip2 mode, and place them under/root/named ceshi.tar.bz2
  
  tar -Jcvf /root/ceshi.tar.xz /boot/ /bin/Archive the/boot/and/bin/directories as a file using XZ mode and place them under/root/named Ceshi.tar.xz
  
  ls-lh/root/ceshi*//List view files starting with Ceshi in the/root/directory
  
  (2) View archived files
  tar -ztvf /root/ceshi.tar.gzView ceshi.tar.gz files that are compressed using gzip
  
  tar -jtvf /root/ceshi.tar.bz2View ceshi.tar.bz2 files that are compressed using the Bzip2 method
  
  tar -Jtvf /root/ceshi.tar.xzView CESHI.TAR.XZ files that are compressed using XZ mode
  
  Note: Tar archive can only be viewed using the corresponding compression method when viewed, such as compression using gzip (-Z)
  (3) Unzip the archive file
  tar -zxvf /root/ceshi.tar.gz -C /tmp/Extract the ceshi.tar.gz archive file using gzip compression to the/tmp/directory
  
  tar -jxvf /root/ceshi.tar.bz2 -C /tmp/Extract the ceshi.tar.bz2 archive file using bzip2 compression to the/tmp/directory
  
  
  tar -Jxvf /root/ceshi.tar.xz -C /tmp/Extract the CESHI.TAR.XZ archive file compressed with XZ mode to the/tmp/directory
  
  
  Note: When the tar is decompressed, the corresponding compression method must be used to decompress the corresponding compression method;

Linux basic Commands (ii)