Category: Operating System

Shell Access via VI or VIM Why do you need to access shell via VI or VIM? A: sometimes, you have to copy result of a commands and paste those results to editor. For example, you are configuring SCSI devices as DM-Multipath devices, you have to run some commands like “multipath -l” for see “WWID” of specific device and add the “WWID” to “multipath.conf”. As simple solution, you can run another ssh session and run the command on this session, then copy and paste the result. But I think, there is another good way to do it. You can access to shell via VI or VIM editor and do your job! But how to? How to Access Shell via VI or VIM? Run VI or VIM command to open the editors and start to edit your file. For accessing to shell, you must run the below command within VI or VIM: :shell Or this command: :sh Then you will access to shell and the editor is still open. The shell is opened for your temporary, so you must have access to editor again. Press Ctrl+D or type “exit” and hit Enter for return back to the editor.

Linux tac Command tac command practically is reverse version of cat command. It means, any result in cat command will be reversed by tac command. tac is lesser known and less used command in Linux but I want to show you the command usage and some examples. Usage and Examples tac command has few options same as cat command, we’ll review some of its options at the below. Example 1 Comparison cat and tac outputs. In this example, we have a file with the below content: [root@localhost ~]# cat sample1.txt This is first line. This is second line. This is third line. This is fourth line. Now, print the file’s content by tac: [root@localhost ~]# tac sample1.txt This is fourth line. This is third line. This is second line. This is first line. Example 2 Both tac and cat commands has separator option which one of the most important options and the command is represented by the -s switch, which separates the contents of the file based on a string or a keyword from the file. [root@localhost ~]# cat sample1.txt —1— 1 2 3 —2 A B C —3– a b c [root@localhost ~]# tac –before –regex –separator=^—[0-9]+-*$ sample1.txt —3–...

Linux Cat Command Cat or “concatenate files and print on the standard output” is a Linux command to print file content on the standard output like screen. This is one of most popular Linux commands. I think that every Linux administrator has executed the below command at least one time 😉 : # cat /var/log/messages So this is actually very useful and popular command. Usage and Examples Cat command has few options but has lot of usages. Show file content: If Cat command run without options, it will shows you the content of the file or files. Show multiple files content: You can view content of multiple files by entering more than one file name in command line, see the below example: Create New File: You be able to create new file by Cat command. Run the below command and then enter some strings and when it’s finished hit Enter, if you are end of a line and then Ctrl+D for save the new file. Please consider that existing files will be overwrite by run same command.   Join Multiple Files: Joining multiple files to a file is possible by Cat command. Here is an example: # cat file1.txt file2.txt file3.txt > all-files.txt...