How to access Tar files in Linux/Unix

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The Linux tar command abbreviation is “tar archive” released under POSIX standards initially and It now follows the GNU standards

Often when you download the files from the internet they are in the .tar, tar.gz. Or tar.bz2 compressed format using either bz2 or gz compression algorithm.

If you are familiar with the Opensource then there’s a good chance that you would have come across the extensions like Package-name.tar, tar.gz, tar.bz, tar.xz which are standard.

Well most open source software use tarballs to distribute programs/source codes in this format as it offers efficient compression and better organized way of grouping files.

It supports a vast range of compression programs such as gzip, bzip2, xz, lzip, lzma, lzop.

In the following tutorial we will show how to Compress/Extract the files into tar.gz or tgz.

How to specify the format POSIX Or GNU while using tar Command?

[vamshi@linuxcent ]$ tar --format=posix -cf posix.tar *
[vamshi@linuxcent ]$  tar --format=gnu -cf gnu.tar *
[vamshi@linuxcent ]$  file posix.tar gnu.tar 
posix.tar: POSIX tar archive
gnu.tar: POSIX tar archive (GNU)

GNU is based on an older POSIX format, So that’s why it says POSIX for both.

To print the contents information of an archived directory, use the directory name as a file name argument in conjunction with --list (-t). To find out file attributes, include the --verbose (-v) option.

Firstly start off by long listing ls in the present directory we have here:

vamshi@LinuxCent:~/Linux> ls
Debian-Distro/  OpenSuse-Distro/ README  Redhat-Distro/

We will now compress the present working directory using Linux GNU’s tar command line utility.. Creating a tar of the current directory mentioned by Asterisk *. The Options -c creates, -v: Verbose mode, -z: Uses GZIP algorithm
Demonstration shown below:
Either one of the following commands can be used

vamshi@LinuxCent:~/Linux> tar --gzip -cvf Linux-flavours.tar.gz *
vamshi@LinuxCent:~/Linux> tar -cvzf Linux-flavours.tar.gz *
Debian-Distro/
Debian-Distro/ubuntu.txt
Debian-Distro/debian.txt
Debian-Distro/README-Debian-Distro
Linux-flavours.tar.gz
OpenSuse-Distro/
OpenSuse-Distro/README-Opensuse-Distro
OpenSuse-Distro/opensuse.txt
README
Redhat-Distro/
Redhat-Distro/Fedora/
Redhat-Distro/Fedora/fedora.txt
Redhat-Distro/Centos/
Redhat-Distro/Centos/centos.txt
Redhat-Distro/Centos/CentOS-versions/
Redhat-Distro/Centos/CentOS-versions/centos7.txt
Redhat-Distro/Centos/CentOS-versions/centos5.5.txt
Redhat-Distro/Centos/CentOS-versions/centos6.9.txt
Redhat-Distro/Centos/CentOS-versions/centos5.8.txt
Redhat-Distro/Centos/CentOS-versions/centos6.1.txt
Redhat-Distro/Centos/README-CentOS
Redhat-Distro/README-Redhat-Distro
Redhat-Distro/RHEL-Versions/
Redhat-Distro/RHEL-Versions/redhat5.txt
Redhat-Distro/RHEL-Versions/redhat7.txt
Redhat-Distro/RHEL-Versions/redhat6.txt
Redhat-Distro/RHEL-Versions/redhat8.txt
Redhat-Distro/redhat.txt

How to List/view Archives

The option-t does a Dry-run of extract operation but only to print the contents of the mentioned compression.

vamshi@LinuxCent:~/Linux> tar -tvf Linux-flavours.tar.gz
Debian-Distro/
Debian-Distro/ubuntu.txt
Debian-Distro/debian.txt
Debian-Distro/README-Debian-Distro
…

How to Extracting tar.gz File?

Extracting the tar file using the options -x works out just fine as -x option chooses the tye of decompression based on the compression file type, and the content will be extracted to current working directory.

Here are various extraction options:

$ tar -xvf Linux-flavours.tar.gz
$ tar -zxvf Linux-flavours.tar.gz
$ tar --gzip -xvf Linux-flavours.tar.gz

The Filter / Options for compression types:
-z or --gzip : Used for Archival operation for .gzip type
-j -r --bzip2: Used for archival operation for .bzip2 type
[/code]-J[/code] or --xz: User for Archival for .xz type

How to Extract Only Specific Files from a compressed tar archive (tar) File

This doesn’t require any special option but you have to name the exact file and directory that you want to extract

[vamshi@linuxcent ~]$ tar -zxvf redmine-4.0.6.tar.gz redmine-4.0.6/bin/about
redmine-4.0.6/bin/about

Successful in extracting only the redmine-4.0.6/bin/about file from the redmine-4.0.6.tar.gz archive.

[vamshi@linuxcent ~]$ ls -l redmine-4.0.6/bin/about 
-rwxrwxr-x. 1 vamshi vamshi 167 Dec 20 11:46 redmine-4.0.6/bin/about

How to Extract specific files or Directories from the archive

vamshi@LinuxCent:/tmp/linux-test> tar -zxvf Linux-flavours.tar.gz Redhat-Distro/Centos/
Redhat-Distro/Centos/
Redhat-Distro/Centos/centos.txt
Redhat-Distro/Centos/CentOS-versions/
Redhat-Distro/Centos/CentOS-versions/centos7.txt
Redhat-Distro/Centos/CentOS-versions/centos5.5.txt
Redhat-Distro/Centos/CentOS-versions/centos6.9.txt
Redhat-Distro/Centos/CentOS-versions/centos5.8.txt
Redhat-Distro/Centos/CentOS-versions/centos6.1.txt
Redhat-Distro/Centos/README-CentOS

 

This way we are able to extract only the specific directories pertaining to Centos from Redhat-Distro.
Now we would do the extraction of the contents on Redhat-Distro and its sub directories.
Extracting Sub-directories inside the compressed tar.gz

How to Extract TAR file Contents to a New directory?

The tar program by default, extracts the archive contents to the present working directory.
By specifying the option --directory (-C) You can extract archive files in a Target directory.

vamshi.santhapuri@LinuxCent:/tmp/linux-test1> tar -xzvf ~/Linux/jdk-8u101-linux-x64.tar.gz  -C /usr/local/

The above operation extracts the java bundle to /usr/local/ directory.

How to extract only the specific directory from the Compression to a Target directory?

vamshi.santhapuri@LinuxCent:/tmp/linux-test1> tar -xzvf ~/Linux/Linux-flavours.tar.gz Redhat-Distro/RHEL-Versions/ -C /tmp/linux-test
Redhat-Distro/RHEL-Versions/
Redhat-Distro/RHEL-Versions/redhat5.txt
Redhat-Distro/RHEL-Versions/redhat7.txt
Redhat-Distro/RHEL-Versions/redhat6.txt
Redhat-Distro/RHEL-Versions/redhat8.txt

How to tar compress the specific Files and Directory and Sub-directories / Multiple Directories using tar command?

Below is the Demonstration of compression program using gz compression.

vamshi@LinuxCent:~/Linux> tar -cvzf Redhat-Distro/ Linux-flavours.tar.gz centos.txt fedora.txt opensuse.txt redhat.txt ubuntu.txt
centos.txt
fedora.txt
opensuse.txt
redhat.txt
Redhat-Distro/centos.txt
Redhat-Distro/fedora.txt
Redhat-Distro/redhat.txt
Redhat-Distro/Redhat-Versions/
Redhat-Distro/Redhat-Versions/redhat5.txt
Redhat-Distro/Redhat-Versions/redhat7.txt
Redhat-Distro/Redhat-Versions/redhat6.txt
Redhat-Distro/Redhat-Versions/redhat8.txt

You can also compress multiple directories and files into a single tar.gz file as demonstrated below

How to exclude particular directories and file from the compression using tar command?

We can make use of the --exclude="DontIncludethisPath" in Linux tar command, where in the base directory of mentioned pattern are excluded.. Lets run the tar command and see the results

vamshi@linuxCent:~/Linux/OSes> tar -czvf exclude-flavours.tar.gz --exclude="Redhat-Distro" .
./
./OpenSuse-Distro/
./OpenSuse-Distro/README-Opensuse-Distro
./OpenSuse-Distro/opensuse.txt
./Debian-Distro/
./Debian-Distro/ubuntu.txt
./Debian-Distro/debian.txt
./Debian-Distro/README-Debian-Distro
tar: .: file changed as we read it

The compression successfully completed and now lets list out the files

vamshi@linuxCent:~/Linux/OSes> ls -lthr
total 16K
drwxr-xr-x 2 vamshi users 4.0K Apr  8 14:09 OpenSuse-Distro
drwxr-xr-x 2 vamshi users 4.0K Apr  8 14:09 Debian-Distro
drwxr-xr-x 5 vamshi users 4.0K Apr  8 14:09 Redhat-Distro
-rw-r--r-- 1 vamshi users  718 Apr 8 19:18 exclude-flavours.tar.gz

From the dry-run extract output of the compression does not contain the Directory Redhat-Distro

vamshi@linuxCent:~/Linux/OSes> tar -tvf exclude-flavours.tar.gz
drwxr-xr-x vamshi/users 0 2020-04-08 19:18 ./
drwxr-xr-x vamshi/users 0 2020-04-08 14:09 ./OpenSuse-Distro/
-rw-r--r-- vamshi/users 0 2020-04-08 14:09 ./OpenSuse-Distro/README-Opensuse-Distro
-rw-r--r-- vamshi/users 9 2020-04-08 13:22 ./OpenSuse-Distro/opensuse.txt
drwxr-xr-x vamshi/users 0 2020-04-08 14:09 ./Debian-Distro/
-rw-r--r-- vamshi/users 7 2020-04-08 13:22 ./Debian-Distro/ubuntu.txt
-rw-r--r-- vamshi/users 7 2020-04-08 13:50 ./Debian-Distro/debian.txt
-rw-r--r-- vamshi/users 0 2020-04-08 14:09 ./Debian-Distro/README-Debian-Distro

 

How to create symbolic Link or Softlinks in Linux and differentiate between Softlink vs Hardlink

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The concept of Links in Linux/Unix based systems is Unique and gives a very deeper understanding of the Linux working internals at various levels.

The symbolic also known as Soft link is a special type of linking that acts as a pointer to the original file present on the disk.

The Softlink span across different filesystems extensively and widely used during software package installation and configuring

Lets look at the example of java command linking:

[root@node02 ]# which java
/bin/java
[root@linuxcent ]# ls -l /bin/java
lrwxrwxrwx. 1 root root 22 Apr 10 11:52 /bin/java -> /etc/alternatives/java
[root@node02 boot]# ls -l /etc/alternatives/java
lrwxrwxrwx. 1 root root 73 Apr 10 11:52 /etc/alternatives/java -> /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.242.b08-0.el7_7.x86_64/jre/bin/java
[root@linuxcent ]#

If you upgrade java on your system then the /bin/java command points out to a newer installed version of /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.242.b08-0.el7_7.x86_64/jre/bin/java

We will see the demonstration of a Symbolic link.

In Linux to make the links between files, the command-line utility is “ln”.

Softlink Creation syntax using the Linux command line utility ln -s option:

ln -s <source file|Directory > <destination Link file|Directory>

Below is an example

[vamshi@linuxcent html]$ ln -sf /var/www/html/index.html /tmp/index.html

[vamshi@linuxcent html]$ ls -l /tmp/index.html

lrwxrwxrwx. 1 vamshi vamshi 24 Apr  1 18:23 /tmp/index.html -> /var/www/html/index.html

 

The second file is called a symbolic ink to /tmp/index.html

Now the second file /tmp/index.html is called a Symbolic link to the First file on the disk /var/www/html/index.html

It means that the second file is just pointing to the first file’s location on disk without actually copying the contents of the file.

[vamshi@linuxcent html]$ cat /var/www/html/index.html
Welcome to LinuxCent.com
[vamshi@linuxcent html]$ cat /tmp/index.html
Welcome to LinuxCent.com

When you edit either of the file, the contents of the original file on disk are directly modified.

 

How to create Softlinks to Directories in Linux ?
The same logic applies to creating the soft links to directories, Lets see the Demonstration below:

[vamshi@linuxcent html]$  ln -sf /var/www/html/linuxcent/static/ /tmp/static
[vamshi@linuxcent html]$ ls -l /tmp/static
lrwxrwxrwx. 1 vamshi vamshi 32 Apr  8 18:37 /tmp/static -> /var/www/html/linuxcent/static/

 

How do we Remove the linking between the files is even simpler.

Simply run the unlink command on its Destination:

Sample command:

unlink <destination Link file | Directory>

Lets see the Demonstration

unlink /tmp/data-dir

 

Understanding Symbolic / Hard link concept better with improving knowledge on Inode.

To better understand the concept of Symbolic linking we need to understand the concept of Inode numbers present in Linux. I will give a brief overview of it in this section But for Detailed Review, Please see the What is Inode in Linux Section.

We can list out the inode number of any file on linux system using [/code]ls -i <filename>[/code]

Now The extreme left column indicates the system wide unique inode number:

[root@node02 ~]# ls -li /var/www/html/index.html /tmp/index.html 
67290702 lrwxrwxrwx. 1 root root 24 Apr 8 19:09 /tmp/index.html -> /var/www/html/index.html
33557754 -rw-r--r--. 1 root root 25 Apr 8 18:19 /var/www/html/index.html

We can see here the inode number for both the files have different, Because the second file is just a pointer to the original source file..

So why do we create the Symbolic Links ?

We have the advantages of the Softlinks

  1. One Advantage of Softlinks/symbolic links is they span across different filesystems
  2. Can have many softlinks to a single file/Directory.
  3. Can create Symbolic Links of Directories and Files respectively.
  4. Rsync program by default preserves the symbolic links.
  5. The softlinks become activated immediately if the source is recreated or recovered after any kinds of network outages.

What are the best practices when using Softlinks ?

The best practice while creating softlinks is to mention absolute path for source and destination links.

On the other hand you should also understand the disadvantages or shortcomings.

  1. It is Important to observe that If the source file is deleted then the symbolic link becomes useless.
  2. Incases of the Network filesystem issues leading to unavailability of softlinks.

It is also Essential to understand about the Hardlinks to get an overall understanding.

 

Creating a hard link is a simple operation using ln command with no options

Sample Command:

$ ln /path/to/source/ /path/to/HardLink/

So lets start of by creating a hard link of our file /var/www/html/index.html

[vamshi@linuxcent linuxcent]$ ln /var/www/html/index.html /tmp/index-hl.html

The command ls -il lists the inode number of the files.

[vamshi@linuxcent  ]$ ls -i
33557752 index-hl.html  33557752 index.html

So to conclude, The hard linking results in the same inode number, howmany ever times the hardlink of same file is created.
The data continues to persists in the same storage location on the filesystem even if one of the hardlink file is deleted.
As long as the inode number is identical on the files, no filename change matters to the filesystem.
There will be no change in Hardlink behaviour.

Let’s add some content to the hardlink file here and see the Demonstration

[vamshi@linuxcent ]$ echo "We are updating the file to check out the Hardlinks" >>  /tmp/index-hl.html
We are updating the file to check out the Hardlinks

The new line is added in the original file.

[vamshi@linuxcent linuxcent]$ cat index.html
Welcome to LinuxCent.com
We are updating the file to check out the Hardlinks

Content manipulations to either of the files will be treated as a same file.

How to Identify how many times a particular file was linked ?

Note that Linux Command ls -li provides the actual link aggregate count information in the fourth column represented by the number 2 here, which means that it has a second hardlink reference and both the files are interchangeable.
And It should be noted that a file has a link count of 1 by default as it references itself

$ls -li
33557752 -rw-rw-r--. 2 vamshi vamshi 59 Apr  8 19:48 index-hl.html
33557752 -rw-rw-r--. 2 vamshi vamshi 59 Apr  8 19:48 index.html

In case either one of the file is deleted, the other file survives and continues to function properly.

Lets see some hard facts on the Hardlinks.

  1. Hardlinks can’t be created to Directories.
  2. They do not span across filesystems.

How to use grep command in Linux and Unix

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The grep command is one of the most essential commands in Unix/Linux ecosystem, It is used to extract match and find the occurrence of string literals and patterns among the text files.

In this section we will focus on the important scenarios and provide the realtime explanation about the Various Grep command options offered in linux command line.

We now have a text file with Following content.

Below is the content of the file called intro.txt.

[vamshi@linuxcent grep]$ cat intro.txt
the first line is in lower case
THE SECOND LINE IS IN UPPER CASE


There following are Most popular Linux server Distributions:
1) Redhat Enterprise Linux
2) Ubuntu
3) Centos
4) Debian
5) SUSE Linux Enterprise Server
This is a Demonstration of Linux grep command

Let’s start with search of a string pattern in the given file

The grep command sample search syntax is

$ grep “string pattern” <filename>
$ cat < filename | * > | grep "string pattern"

Lets see the Demonstration

[vamshi@linuxcent grep]$ grep "Linux" intro.txt
There following are Most popular Linux server Distributions:
1) Redhat Enterprise Linux
5) SUSE Linux Enterprise Server
This is a Demonstration of Linux grep command

Searching for a pattern on multiple files using grep command

Lets see the Demonstration

[vamshi@linuxcent grep]$ grep "Linux" intro.txt intro-demo.txt
intro.txt:There following are Most popular Linux server Distributions:
intro.txt:1) Redhat Enterprise Linux
intro.txt:5) SUSE Linux Enterprise Server
intro.txt:This is a Demonstration of Linux grep command
intro-demo.txt:There following are Most popular Linux server Distributions:
intro-demo.txt:1) Redhat Enterprise Linux
intro-demo.txt:5) SUSE Linux Enterprise Server
intro-demo.txt:This is a Demonstration of Linux grep command

 

How to print the sequence number of matched pattern in file using Grep command in Linux?

Print the sequence number of lines that contain the matched string pattern can be achieved using -n Option:

[vamshi@linuxcent grep]$ grep -n "Linux" intro.txt
4:There following are Most popular Linux server Distributions:
5:1) Redhat Enterprise Linux
9:5) SUSE Linux Enterprise Server
11:This is a Demonstration of Linux grep command

The -b Option prints the subsequent starting offset index of the matching word from the lines within the given filename.

[vamshi@linuxcent grep]$ grep -b "Linux" intro.txt
66:There following are Most popular Linux server Distributions:
127:1) Redhat Enterprise Linux
184:5) SUSE Linux Enterprise Server
217:This is a Demonstration of Linux grep command

So far we have seen only the matching string pattern, but if you want to find the occurance of particular word then use grep -w Option

Lets us see the Demonstration below:

[vamshi@linuxcent grep]$ grep -w "Cent" intro.txt

And As expected here we have not seen any occurrence of the word Cent from the file although the word Centos was present, But it didnt match because we used -w option to match the word Cent.

But when we grep for the Word Linux then we can see the exact occurrence of the word and the matching lines are printed.

[vamshi@linuxcent grep]$ grep -w "Linux" intro.txt
There following are Most popular Linux server Distributions:
1) Redhat Enterprise Linux
5) SUSE Linux Enterprise Server
This is a Demonstration of Linux grep command

This can be used in conjunction with -o prints only completely matched word string pattern.

[vamshi@linuxcent grep]$ grep -w -o "Linux" intro.txt
Linux
Linux
Linux
Linux

How to use the Invert Option in Linux grep command

The -v option prints all the lines not matching the given string pattern.

[vamshi@linuxcent grep]$ grep -v "Linux" intro.txt
the first line is in lower case
THE SECOND LINE IS IN UPPER CASE


2) Ubuntu
3) Centos
4) Debian

 

How to print the names of all the files matching the string pattern using Linux Grep command.

Using the -l Option of grep command will print all the file names containing the matching string pattern/string literal

[vamshi@node02 grep]$ grep -l Linux *
intro-demo.txt
intro.txt

How to get the number of Count Matches using Grep command ?

In Linux Grep command we can use the Option -c to get the total occurance Count of the matching pattern/string

Lets see the Demonstration below

[vamshi@linuxcent grep]$ grep -c "Linux" intro.txt
4

How to Exclude specific Directories while searching with grep command ?

The --exclude-dir="Some Directory name" options skips the contents of the mention directory Lets see the Demonstration:

$ grep -w -E "data" * -R --exclude-dir="backup" --exclude-dir="adb-fastboot" --exclude-dir="IntelliJ-IDEA"

How to use Linux Grep commmand to ignore the case  OR perform Case Insensitive search ?

Linux Grep Command offers the -i to skip the case and perform the search.

[vamshi@linuxcent grep]$ grep -i Cent intro.txt
3)Centos

Lets search for the Work Upper from the file with -i option

[vamshi@linuxcent grep]$ grep Upper -i intro-demo.txt
THE SECOND LINE IS IN UPPER CASE

How to Grep for the lines before and After the pattern occurrence in a file

We can use the below options in Linux Grep command to extract the N number of lines matching the containing pattern before/After from the given file.. Lets look at the Options in detail

Generic Syntax:

grep -<A|B|C> “string pattern” filename*

Lets see the Demonstration as follows:

-A: Prints N number of lines After the pattern match and the line containing the match

[vamshi@linuxcent grep]$  grep -A2 docker /etc/passwd
dockerroot:x:996:992:Docker User:/var/lib/docker:/sbin/nologin
mysql:x:27:27:MariaDB Server:/var/lib/mysql:/sbin/nologin
ntp:x:38:38::/etc/ntp:/sbin/nologin

-B: Prints N number of lines Before the pattern match and the line containing the match

[vamshi@linuxcent grep]$  grep -B2 docker /etc/passwd
apache:x:48:48:Apache:/usr/share/httpd:/sbin/nologin
builduser1:x:1002:1002::/home/builduser1:/bin/bash
dockerroot:x:996:992:Docker User:/var/lib/docker:/sbin/nologin

-C: Prints the line Containing the pattern and the N number of lines Before and After

[vamshi@linuxcent grep]$ grep -C2 docker /etc/passwd
apache:x:48:48:Apache:/usr/share/httpd:/sbin/nologin
builduser1:x:1002:1002::/home/builduser1:/bin/bash
dockerroot:x:996:992:Docker User:/var/lib/docker:/sbin/nologin
mysql:x:27:27:MariaDB Server:/var/lib/mysql:/sbin/nologin
ntp:x:38:38::/etc/ntp:/sbin/nologin

Linux Grep command using the Regular Expression (regex) search pattern

How to use the Special Meta-characters in Grep Command

The Special Meta-Character ^ (caret) symbol to match expression at the start of a line.
Practical examples of grep command using meta-characters are as follows:

[vamshi@linuxcent grep]$ grep ^root /etc/services
rootd           1094/tcp                # ROOTD
rootd           1094/udp                # ROOTD

$ (dollar) symbol to match expression at the end of a line

[vamshi@linuxcent grep]$ grep "bash$" /etc/passwd
root:x:0:0:root:/root:/bin/bash
vagrant:x:1000:1000:vagrant:/home/vagrant:/bin/bash
vamshi:x:1001:1001::/home/vamshi:/bin/bash
jenkins:x:997:994:Jenkins Automation Server:/var/lib/jenkins:/bin/bash
builduser1:x:1002:1002::/home/builduser1:/bin/bash
linuxcent:x:1003:1004::/home/linuxcent:/bin/bash

Another Bonus regex for evading Empty lines from a text file using the Meta-characters ^ Carat and $ Dollar Symbols.

[vamshi@node02 grep]$ grep -Ev "^$" intro.txt
the first line is in lower case
THE SECOND LINE IS IN UPPER CASE
There following are Most popular Linux server Distributions:
1) Redhat Enterprise Linux
2) Ubuntu
3) Centos
4) Debian
5) SUSE Linux Enterprise Server
This is a Demonstration of Linux grep command

As the result of the above command observed Empty lines in our text file are now excluded with the inverted matching of Empty line pattern expression.

Digit Matching operation using Linux Grep Command

The Grep command Option -P offers the perl-regex pattern matching to perform some of the tricky pattern matching conditions, Lets see the Demonstration.

[vamshi@linuxcent grep]$ grep -P "[\W][\d][\d]/" /etc/services

Now we Demonstrate Numerical pattern matching in the following ways to match the exact occurrence of IPv4 address

[vamshi@linuxcent grep]$ ip a |grep -E "[0-9].[0-9].[0-9].[0-9]"
inet 127.0.0.1/8 scope host lo
inet 10.100.0.20/24 brd 10.100.0.255 scope global noprefixroute eth1

The similar result can be extracted using -P, Demonstrated as below:

[vamshi@linuxcent grep]$ ip a  | grep -P "[\d].[\d].[\d].[\d]"
inet 127.0.0.1/8 scope host lo
inet 10.100.0.20/24 brd 10.100.0.255 scope global noprefixroute eth1

Highlighting the Search patterns with Color codes

If you want to highlight the search pattern from the output we can make use of Color code Option is grep

[vamshi@linuxcent ~]$ ps -ef |grep java --color=yes

 

grep command and the Meta-characters with practical examples

In the Extended Regular Expression the metacharacters ?, \+, \{,  \|, \(, and \) enhances and takes the search string to manifest into a rich pattern

The square brackets [/code][ ][/code] includes a list of characters and it matches a single character in the list. Within the bracket, we can specify a  range, like [a-z] [0-9] [abcd], But it only matches a single character in the give list range.
The brackets can contain the carat ^ or the $ symbols and can be globbed with the wildcard characters for finding the repetitive pattern.

Here we shall see the demonstration of a few metacharacters conjunction into a single grep command

Using the Infix Operator | with the meta-characters

$ dmesg -H | egrep '(s|h)d[a-z]'

A quick practical look at the dmesg to find about the errors and warnings using grep command.

$ dmesg -H | grep -Ei “error|warn”

How to find the exact work match for the word error or err with a blank white space at the start of the word from dmesg?
$ dmesg -H | grep -Ei “(er)[r]{1,2}(or)”
$ dmesg -H | grep -Ei “(\We)[r]+(or)|(\Werr)”

Explanation: The grep search metacharacter regular expression matches the occurring of the string literals “error” with the minimum 1 time occurrence (error) of literal r and maximum 2 times.

The output only prints lines containing the word “error“ in a case insensitive grep search.

 

Another great practical example here we apply the same logic to enhance the metacharacter regex pattern to search for the occurrence of error with but without a trailing colon “:” symbol

dmesg -H | grep -Ei “(error)[:]{0}”

 

Linux Copy File Command for Files and Directories – cp Command Examples

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Linux copy files command: cp is generally used for organizing the data on the Linux operating system, It copies the files and directories.

We shall take a deeper look at Linux cp command-utility in the section

In order to copy files and directories, you must have read permissions on the source file(s) and write permissions on the destination directory

How do I copy files under Linux operating systems?

How do I make a 2nd copy of a file on a Linux bash shell?

How can I copies files and directories on a Linux

Linux Copy File command Syntax

cp sourcefile destinationfile
cp sourcefile DESTDIR
cp sourcefile1 sourcefile2 DESTDIR
cp [OPTION] SOURCE DESTFILE
cp [OPTION] SOURCE DESTDIR

How to Copy a Directory if the destination does not exist?

To achieve this we can make use of the following cp command options -R or -r: Copy directories recursively.

Linux cp command Syntax with -R option:

cp -R SOURCE DESTINATION

If the destination doesn’t exist, it will be created.

It can also be used to Copy the contents Recursively

Lets see the demonstration as follows:

[vamshi@linuxcent ]$ cp -R dir1/ dir1-copy
[vamshi@linuxcent ]$ ls -l 
total 0
drwxrwxr-x. 2 vamshi vamshi 6 Apr 11 06:35 dir1
drwxrwxr-x. 2 vamshi vamshi 6 Apr 11 06:37 dir1-Recursive

Using the verbose Option -v to print the copy activity information onto the output screen.

Let’s use the -v flag to print the verbose information onto the screen.

How to Preserve the Source file and Directory permission?

Linux Copy command Syntax with -p option:

-p option preserves the mode, ownership and timestamps from the source to the destination

cp -p file1 file1-copy

Lets us see the Demonstration as Below

[vamshi@node02 cp-command]$ cp -Rp dir1/ dir1-copy
[vamshi@node02 cp-command]$ ls -ld dir1*
drwxrwxr-x. 2 vamshi vamshi 6 Apr 11 06:35 dir1
drwxrwxr-x. 2 vamshi vamshi 6 Apr 11 06:35 dir1-copy
drwxrwxr-x. 2 vamshi vamshi 6 Apr 11 06:37 dir1-Recursive

From the out we can conclude the the Linux copy command with -p Option preserves the original timestamps information and copies it to the destination

Linux cp command with Force copy -f Option, It forcefully overwrites the destination content
Sample Syntax:

cp -f file1 file1-copy

How to Copy Multiple files at once ?

Asterisk / wildcard (*) character is used to copy files multiple files with same pattern.

[vamshi@linuxcent ]$ cp -varpf file* DEST/
‘file10.txt’ -> ‘DEST/file10.txt’
‘file1.txt’ -> ‘DEST/file1.txt’
‘file2.txt’ -> ‘DEST/file2.txt’
‘file3.txt’ -> ‘DEST/file3.txt’
‘file4.txt’ -> ‘DEST/file4.txt’
‘file5.txt’ -> ‘DEST/file5.txt’
‘file6.txt’ -> ‘DEST/file6.txt’
‘file7.txt’ -> ‘DEST/file7.txt’
‘file8.txt’ -> ‘DEST/file8.txt’
‘file9.txt’ -> ‘DEST/file9.txt’

The options -p or -d enables preserving the links and can be used in conjunction with -R option to copy contents Recursively from the source directory.

How to Copy Files and Folders on Linux Using the cp Command recursively to Destination Directory

How to preserve the links with cp command?

Using the Options -p preserves the links and -r Option copies the content recussively same as -R Option and -v prints the verbose information

[vamshi@node02 Linux-blog]$ cp -varpf Redhat-Distro/ /tmp/DEST
‘Redhat-Distro/’ -> ‘/tmp/DEST’
‘Redhat-Distro/Fedora’ -> ‘/tmp/DEST/Fedora’
‘Redhat-Distro/Fedora/fedora.txt’ -> ‘/tmp/DEST/Fedora/fedora.txt’
‘Redhat-Distro/Centos’ -> ‘/tmp/DEST/Centos’
‘Redhat-Distro/Centos/centos.txt’ -> ‘/tmp/DEST/Centos/centos.txt’
‘Redhat-Distro/Centos/CentOS-versions’ -> ‘/tmp/DEST/Centos/CentOS-versions’
‘Redhat-Distro/Centos/CentOS-versions/centos7.txt’ -> ‘/tmp/DEST/Centos/CentOS-versions/centos7.txt’
‘Redhat-Distro/Centos/CentOS-versions/centos6.1.txt’ -> ‘/tmp/DEST/Centos/CentOS-versions/centos6.1.txt’
‘Redhat-Distro/Centos/README-CentOS’ -> ‘/tmp/DEST/Centos/README-CentOS’
‘Redhat-Distro/README-Redhat-Distro’ -> ‘/tmp/DEST/README-Redhat-Distro’
‘Redhat-Distro/RHEL-Versions’ -> ‘/tmp/DEST/RHEL-Versions’
‘Redhat-Distro/RHEL-Versions/redhat5.txt’ -> ‘/tmp/DEST/RHEL-Versions/redhat5.txt’
‘Redhat-Distro/RHEL-Versions/redhat8.txt’ -> ‘/tmp/DEST/RHEL-Versions/redhat8.txt’
‘Redhat-Distro/redhat.txt’ -> ‘/tmp/DEST/redhat.txt’

How to make a symbolic link with Linux cp command to files ?

As we know that ln command us useful to create symboic links, But the Linux copy command Syntax can do that to files with -s Option which creates Symbolic links:

cp -s SOURCE DESTINATION

Linux copy command Syntax with Softlink with Demonstration:

[vamshi@linuxcent ~]$ ls -l total 0
-rw-rw-r--. 1 vamshi vamshi 0 Apr 11 06:39 file1.txt

lrwxrwxrwx. 1 vamshi vamshi 9 Apr 11 06:39 file2.txt -> file1.txt

Linux cp command with interactive prompt using -i option

Sample Syntax:

cp -i file1 file1-copy

Also you can make it a best practice to setup alias alias for cp command.
The best practice is enable options -av

cp -av SOURCE DESTINATION
export cp="cp -av"

How can i copy the hidden files ?

To Copy the hidden files we can use cp command with -a option,lets us see in a practical example.

$ cp -av source/ destination/
‘source/.config1’ -> ‘destination/source/.config1’
‘source/.config2’ -> ‘destination/source/.config2’
‘source/.config3’ -> ‘destination/source/.config3’

Generally the hidden files in Linux are prefixed with a dot . So we can also use the wildcard character *, and copy them, below is another pracctical example

[vamshi@linuxcent cp-command]$ cp -av source/.conf* destination/
‘source/.config1’ -> ‘destination/.config1’
‘source/.config2’ -> ‘destination/.config2’
‘source/.config3’ -> ‘destination/.config3’

How to Copy a File from One Location to Another With a Different Name on Linux Using the cp Command

Assuming we have a couple of users on our linux server called Alice and Bob

[alice@linuxcent ~]$ sudo cp -avrpf /home/alice/djangoproject1/ /home/bob/
‘djangoproject1/’ -> ‘/home/bob/djangoproject1’
‘djangoproject1/__init__.py’ -> ‘/home/bob/djangoproject1/__init__.py’
‘djangoproject1/asgi.py’ -> ‘/home/bob/djangoproject1/asgi.py’
‘djangoproject1/settings.py’ -> ‘/home/bob/djangoproject1/settings.py’
‘djangoproject1/urls.py’ -> ‘/home/bob/djangoproject1/urls.py’
‘djangoproject1/wsgi.py’ -> ‘/home/bob/djangoproject1/wsgi.py’
‘djangoproject1/__pycache__’ -> ‘/home/bob/djangoproject1/__pycache__’
‘djangoproject1/__pycache__/__init__.cpython-36.pyc’ -> ‘/home/bob/djangoproject1/__pycache__/__init__.cpython-36.pyc’
‘djangoproject1/__pycache__/settings.cpython-36.pyc’ -> ‘/home/bob/djangoproject1/__pycache__/settings.cpython-36.pyc’

How to backup files using cp command?

The linux cp command offer the option --backup to backup the data files, below is the command.

cp --backup source destination