Editing a File

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TODO: {{#todo:SEOKWREV (11.25.13-16:10->KY+);(11.26.13-19:55->MD+);(12.17.13-12:45->MG+);(03.06.14-14:40->BS-);(04.10.14-14:35->BS+)|Klint Youngmeyer|oe 4,oe 5,ky,md,mg,bs,SEOKWREV}}

EMAC OE provides simple text editing capabilities for making changes to configuration files and scripts. Major editing tasks should be performed on a desktop system first, copying the desired files back to the target board. There are two text editors available on standard EMAC OE builds: vi and nano. vi is a very common text editor available on almost every Unix-like OS. nano is a more conventional text editor that can be easier to use for those not familiar with vi.

Using Vi

The key to using vi is understanding the two modes of operation: command mode and insert mode. Command mode is used for navigating the text, search and replace, pasting, saving, and running other commands. Insert mode is used for simply inserting text into the document. The editor will start in command mode. To switch from command mode to insert mode, type "i". To switch from insert mode to command mode, press ESC. Any keys pressed after switching to command mode will be interpreted as vi commands. Some of the most important commands are those for saving and exiting, such as :wq to save and exit. See Table 5 below for a description of some common vi commands.

Table 5: Common Vi Commands
Command Description
:wq Save changes (write) and exit
:q! Discard changes (if any since last write) and exit
:q Exit only if no unsaved changes
x Delete character under cursor
dd Delete current line
yy Yank (copy) current line
p Put (paste) after position
:%s/string/replace/g Replace all occurrences of "string" with "replace"

To open a file using vi simply type the command vi followed by the file name. For example, to edit the network interfaces configuration:

root@emac-oe:~# vi /etc/network/interfaces

For more information about the busybox version of vi, see the following links:

On desktop Linux, the vimtutor program is usually installed with the full vim package. This program is a great way to learn the basics of vim (which stands for VI iMproved) quickly. The vimtutor program is designed to take about a half an hour to work through. The unusual user interface of vi makes it a very powerful editor, once learned. Keys used in the command mode of vi can be found in many other places, as well, such as the gmail web interface (when enabled).

Using Nano

nano is easier to use than vi, but is much less powerful.

After opening a file with nano, the available commands for working with the file will be displayed at the bottom of the screen as shown below:

^G Get Help     ^O WriteOut     ^R Read File    ^Y Prev Page    ^K Cut Text     ^C Cur Pos
^X Exit         ^J Justify      ^W Where Is     ^V Next Page    ^U UnCut Text   ^T To Spell 

For example, to save the file, press Ctrl-O. To exit, press Ctrl-X. The nano editor is always in insertion mode, so any keys typed that are not part of a control sequence will be placed in the file as text. There is no need to press any escape code to switch between entering text and command mode, as is required with vi. To edit a file with nano, pass the name of the file as an argument to the nano command. For example:

root@emac-oe:~# nano /etc/network/interfaces