How do I display line numbers in vim running on Linux or Unix-like operating systems?
[continue reading…]

I am a brand new user of a Linux iptables and I can’t find how to instruct my iptables to delete or unblock an IP address listed in iptables firewall. I’m using Debian Linux version. Can you help please?
[continue reading…]

How do I display vi / vim text editor line numbers while writing a shell script or c program? How can I turn on or off this feature on a Linux, Apple OS X/macOS, or Unix-like operating systems? How cah I make the vi text editor display or hide line numbers? How can I enable line numbers on vim startup by editing the ~/.vimrc config file?
[continue reading…]

Q. How do I number each line of a text file? How do I write a shell script to display text file with line numbers added?
[continue reading…]

How do I print line numbers on the printer for my c / java / c++ code written using vi or vim text editor under Linux / UNIX like operating system?
[continue reading…]

Q. I’ve just installed CentOS Linux server and started to use vi text editor to make changes to config files. How do I perform search and replace operation using vi / vim text editor?

A. vi (vim) is not difficult to learn, the vi editor is well known and used for both writing code and editing config files.

VI search and replace command format

Simple format is as follows:
%s/old-string/new-string/

VI search and replace command examples

Let us say you would like to find a word called “foo” and replace with “bar”.

First hit [Esc] key

Type : (colon) followed by %s/foo/bar/ and hit [Enter] key.
:%s/foo/bar/
Above command will replace first occurrence of word foo with bar on all lines. The % is shorthand for all lines.

To replace all occurrences of word foo with bar on all lines, use the g option (which indicates all occurrences on a line).
:%s/foo/bar/g

Note that the g can be replaced with a number 1,2,…N to change only the n’th occurrence on each line.

Use find and replace on line ranges (match by line numbers)

You can also make changes on range of lines i.e. replace first occurrence of foo with bar on lines 5 through 20 only, enter:
:5,20s/foo/bar/

Following command will replace first occurrence of foo with bar starting at the current line for the next 100 lines:
:.,+100s/foo/bar/

Match by words

Finally, you can match by words i.e. replace first occurrence of foo with bar starting at at the next line containing a word “test”:
:/test/s/foo/bar/g
As usual you can specify ranges:
:/test/,/guest/s/foo/bar/g

Please note that all search/replace commands should be start with the [ESC]: keystroke combination only.