Tag: Linux Basics

Linux man (manual) Command

  • Linux man Command
    Linux man Command

Despite the ‘man’ commands, relative simplicity and appearance of unimportance, the ‘man’ command is, perhaps, one of the most important commands to lean in Linux. 

Why the ‘man’ command important?

The true value of the ‘man’ command is that provides access to the online manuals (documentation), which will be consulted often until Linux commands and functions have to be learned and internalized.  Even after learning the more familiar and commonly used Linux command and functions, one will still need to refer the less commonly used capabilities or to confirm something which has been used in a while.

When some the more arrogant Linux users will sometime tell folks with questions to “read the frickin’ manual” (RTFM), the ‘man’ command is what they are usually talking about.  Although there are other perfectly useful reference materials online (e.g., git documentation project) or commercial books, the ‘man’ command should be the go-to place for documentation.  The reason this is actually very simple, if the command or function is installed in your version or environment instance of Linux, then man pages will be available.  Therefore, usually, there will no need to go search on the internet for answers or carrying books around.

The ‘man’ command syntax

The syntax of the ‘man’ command is simple and easy to learn to use.  In fact, the ‘man’ command is so easy to use that people frequently will not even use options when they use the man command and enter ‘man’ command and the keyword.

‘man’ command syntax

man [options] (keywords)

Simple examples to illustrate how to use the ‘man’ command.

Example to pull up the ‘Man’ command documentation

[blog-server ~]$ man man

In this example, the man command is using ‘man man’ to pull up its own online documentation.

Example to pull up the ‘ls’ command documentation

[blog-server ~]$ man ls

In this example, the man command is using ‘man ls’ to pull up the ‘list directory contents‘ online documentation.

list directory contents

Example to pull up the ‘cp’ command documentation

[blog-server ~]$ man cp

In this example, the man command is using ‘man cp’ to pull up the ‘copy files and directories ‘ online documentation.

Example screenshot of the ‘cp’ (copy files and directories) file command online documentation

  • copy files and directories screenshot
    copy files and directories screenshot

How to install locate command in Linux Redhat and Centos

  • Linux yum Command
    Linux yum Command

To install the locate command (mlocate) in Redhat or Centos, use the ’YUM’ command, install function. 

  • Logon as ‘root’ or use with ‘sudo’ permissions
  • Then, run a ’man’ command to confirm that the locate command is not already installed: ‘man locate’

Example ‘man’ command (as root user)

[root@blog-server ~]# man locate

  • If the ’man’ documentation page returns, then it is already installed.  If no ’man’ documentation page is returned, then run the ‘yum install’ command.
  • Run the ‘yum install’ command as ‘root’ or ‘sudo’ user:

Example ‘yum install’ command (as root user)

[root@blog-server ~]# yum install mlocate

Example ‘yum install’ command (as sudo user)

[root@blog-server ~]# sudo yum install mlocate

Then run the [root@data-server ~]# updated

Example Run ‘updatedb’ Command (as Root user)

[root@blog-server ~]# updated

Example Run ‘updatedb’ Command (as sudo user)

[root@blog-server ~]# sudo updatedb

How To quit the Linux vi editor without saving changes

  • Linux VI Commands
    Linux VI Commands

To quit the Linux ’vi’ editor without saving any changes which have been made:

To Exit the insert or append mode

  1. From within insert or append mode, press the ‘Esc‘ key.

To Enable VI Command Line

  1. Press the ‘:’ (colon) Key. The cursor should reappear in the lower-left corner of the screen beside a colon prompt.
  2. Then, Enter the ‘q!’ Command and press the ‘Enter’ Key.

Example VI Command Line

: q!

This will quit the Linux VI editor, and all changes the document made in this session will be lost.

Linux Move (mv) Command

  • Linux Move (mv) Command
    Linux Move (mv) Command

The Linux move command (mv) is one of the essential commands, which can be very useful in Linux, Unix, and AIX.  The primary purpose of the move command is obviously to move files, and of course, directories.   The move command may also be used to rename files and to make backups.

Move Command Syntax

$ mv [options] source (file or directory)  destination

Move Command options

option description
mv -f force move by overwriting destination file without prompt
mv -i interactive prompt before overwriting
mv -u update – move when the source is newer than the destination
mv -v verbose – print source and destination files
MV – t explicitly saying to move the file or directory here, rather trying to fit everything into the last argument.
mv * Move all (Multiple) files to a specific director without listing by name

For More move command details see the Linux documentation manuals using the man command

$ man mv

mv command examples

Here are some quick and very simple move command (MV) examples for reference.

Move Move to files  to the /Archive/ directory:

$ mv happy.txt garden.txt /Archive/

Move all “.txt” files in the current directory to subdirectory backup:

$ mv *.txt backup

Move all files in subdirectory ‘backup’ to current directory:

$ mv backup/*

Rename file happy.txt to happy.bak filename:

$ mv happy.txt happy.bak

Rename directory backup to backup2:

$ mv backup backup2

Update – move when happy.txt is newer or missing in target directory:

$ mv -u happy.txt backup

Move happy.txt and prompt before overwrite backup / happy.txt:

$ mv -v happy.txt backup

Linux VI Command – Set Line Number

  • VI Display Line Numbers
    VI Display Line Numbers

The “Set Number” command in the VI (visual instrument) text editor seems may not seem like the most useful command.  However, it is more useful than it appears.  Using the “set number” command is a visual aid, which facilitates navigation within the VI editor. 

To Enable Line Number In the VI Editor

The “set Number” command is used to make display line numbers, to enable line numbers:

  • Press the Esc key within the VI editor, if you are currently in insert or append mode.
  • Press the colon key “:”, which will appear at the lower-left corner of the screen.
  • Following the colon enter “set number” command (without quotes) and press enter.

A column of sequential line numbers will then appear at the left side of the screen. Each line number references the text located directly to the right. Now you will know exactly which line is where and be able to enter a colon and the line number you want to move to and move around the document lines with certainty.

To Disable Line Number In the VI Editor

When you are ready to turn offline numbering, again follow the preceding instructions, except this time, enter the following line at the : prompt:

  • Press the Esc key within the VI editor, if you are currently in insert or append mode.
  • Press the colon key “:”, which will appear at the lower-left corner of the screen.
  • Following the colon enter “set nonumber” command (without quotes) and press enter.

To Make The Line Number Enable When You Open VI:

Normally, vi will forget the setting you’ve chosen once you’ve left the editor. You can, however, make the “set Number” command take effect automatically whenever you use vi on a user/account, enter the “set Number” command as a line in the .exrc file in your home directory.

Related References

Useful Links – Linux

  • Linux - Useful References
    Linux – Useful References

Here are a few useful references for Linux, which may be helpful.

Linux Documentation

  • BASH Bourne-Again SHell
    BASH

Bash Documentation

Links for Major Linux Distributions

  • Centos Linux
    Centos Linux

CentOS

  • Red Hat Enterprise Linux (RHEL)
    Red Hat

Red Hat Enterprise Linux (RHEL)

  • Ubuntu Linux
    Ubuntu Linux

Ubuntu

  • IBM
    IBM
  • ORACLE
    ORACLE

The most Important Linux Distributions To Learn Professionally

  • The most Important Linux Distributions To Learn Professionally
    The most Important Linux Distributions To Learn Professionally

Many of us either want a way to import our Linux knowledge, improve our technical career options or perhaps, move into the technology career.  To do any of these efficiently them, the first step would be to focus on the major Linux distribution used by employers. 

The most adapted distributions Linux are Red Hat Enterprise Linux (RHEL) and Ubuntu, so, of the multitude of Linux distributions available, these would be the to learn if you want to move your career forward.

However, if you are seeking an inexpensive alternative to hone your Linux skills at home, then CentOS, is likely your best choice since it is free and is pretty much a copy of RedHat.

Related References