Sunday, December 25, 2016

Essentials of Vi editor - part 3

In my previous two posts (1 and 2 below) we looked at vi basic and editing.

1. Essentials of Vi editor - part 1
2. Essentials of Vi editor - part 2


In this post let's look at few advanced commands and techniques we can use in vi editor

Indentation and work wrapping
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>> indent the current line. e.g 3>> indents 3 lines, >} indents a paragraph
<< outdents the current line
:se ai // Enables auto indent
:se noai // Disables auto indentation
:se wm=8 // Sets the wrap margin to 8. As soon as you enter 8 columns it wraps the cursor
:se wm=0 // Auto wrap set off


Filtering
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!! - applies the filter to the current line
n!! - applies the filter to n number of lines from current line
!} - filters the next paragraph
!{ - filter the previous paragraph
!% - applies the filter from current location to next parranthesis, brace or bracket


These filters can be can be applied to shell commands like tr (transformation), fmt (formatting), grep (search), sed (advanced editing) or awk (a complete programming language). This would mean like sending the filtered text through these commands and getting the output of it and searching or placing back in file as applicable.

e.g In command mode uf you type
!!tr a-z A-z // And enter. Turns the current line into uppercase. Note however your lower command shows :.!tr a-z A-Z. It converts into a format that vi understands it.
5

Advanced examples with : command
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: 1,. d        // Delete all the lines from the first line (indicated by 1) to current line (indicated by .)
: .,$ s/test/text/g   // From current line (indicated by .) to end of line (indicated by $) search and replace all 'test' occurrences to 'text'
: /first/,/last/ ! tr a-z A-Z // Find first line that matches 'first' regexp to the first match following 'last' regex and filter it (indicated by !) using the unix command tr from a-z to A-Z (means convert to upper case)

ma // marks a line by character 'a'
mb // marks a line by character 'b'
!a // jump to the line marked by a
: 'a,'b d // Delete all the lines marked by a through b 

Essentials of Vi editor - part 2

In the previous post we looked at some of the basics of the vi editor. In this post let's walk through searching, replacing and undoing.

Search and Replace
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/text - searches the text.
?text - searches backward
n - repeats the previous search
N - repeats the previous search in backward direction

. matches any single character e.g - /a.c matches both abc, adc etc. Doesn't match 'ac'
\ has special meaning. e.g - /a\.c matches a.c exactly
   e.g - /a\\c matches a\c, /a\/c matches a/c
^ - matches line beginning. e.g - /^abc matches lines beginning with abc
$ - matches line ending e.g - /xyz$ matches lines ending with xyz
[] - matches single character in a set. e.g - /x[abc]y matches xay, xby and xcy
e.g - /x[a-z]y matches xzy, xay etc
e.g - /x[a-zA-Z]y matches xay, xAy etc
e.g - /x[^a-z]y // matches x followed by anything other than a lowercase letter followed by y. Therefore 'xay' doesn't match, but xBy matches.
* - zero or more matches. e.g - xy*z matches xyz, xyyyyz and also xz
\( \) - e.g - /\(xy\)*z matches xyz, xyxyx, xyxyxyz etc
/<.*> - matches <iwhewoip> and <my_name> etc
/<[^>]*> - matches anything in between <>

:s/old/new/   - replaces the first occurrences of old to new on current line
:s/old/new/g - replaces all in the current line

:%s/old/new/   - replaces the first occurrences of old to new of every line in the document
:%s/old/new/g - globally replace all occurrences in the document


You may use any special character other than / for delimitation. For example you may use | or ;

Few special examples.
:%s/test/(&)/g - Here the replacement string is (&), Here the & says the current match. Therefore whatever test words in the document will be put into parenthesis as in (test) 

Undoing
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u - undoing the last change in command mode
Ctrl + r - Redo the last change
U - undo all fhe changes in the current line
. (period) - Repeats last change in your cursor locations

yy - yanks (copy) a line (Similar to dd like delete equivalents) - the yanked texts goes to vi's buffer not to the OS clip-board
yw - yanks a word (just like dw deletes a word)
p - pastes the yanked text after the cursor
P - pastes the yanked text before the cursor

Essentials of Vi editor - part 1

I'm sure if you are a serious programmer that you would agree vi is a programmers editor. Knowing vi's commands and usage helps you a lot with your programming tasks and undoubtedly it's a light weight powerful toolkit in your arsenal. In this post I would like to refresh your know-how on vi commands and usage, although there are hundreds of posts and cheat sheets available online. Some commands are extremely common whereas there are few I think which is not so common but extremely powerful. I cover these using three posts.

Moving around the files
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H (left) , J (down), K (up) , L (right)
w (move forward by one word), b (move backward by one word)
e (move forward till end of current word)
) (Forward a sentence), ( (Bacward a sentence)
} (Forward a full paragraph), { (Backward a full paragraph)

^ (Move to beginning of a line)
$ (Move to end of a line)
% (Matching bracket or brace)

Shift+g (Jump to end of file)
1 and then Shift+g (Jump to beginning of the file)

This works to jump on to a line as well.
e.g: 23 and then Shift+g (Jump to line 23)

Ctrl+e // scroll down one line
Ctrl+y // Scroll up one line
Ctrl+d // Scroll down half a screen
Ctrl+u // Scroll up half a screen
Ctrl+f // Scroll down a full screen
Ctrl+b // Scroll up a full screen



Getting the status of the file
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Ctrl+g    // Shows if the file is modified, the number of lines and the percentage the current line is from the beginning)


Saving and quitting
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:w (Saves the file into the disk and keeps it open)
:wq (Save and close the file) // Equivalent to Shift + ZZ
:q (Quit without saving an unedited file. Warns you if edited)
:q! (Quite without saving even if the file is edited)
:vi <filename> // Closes the current file and open the <filename>. Equivalent to :q and then issuing vi <filename>. If the current file is edited as :q does, a warning will be given
:vi! <filename> // Does the same as above but doesn't warn you. Equivalent to :q! and then issuing vi <filename>.


e.g:

vi file1.txt file2.txt  // loads both file into memory and shows the file1.txt

:n // Shift to the next file
:N // Shift back to the previous file
:rew  // Rewind to first file if you have multiple files open

:r // read a file and insert into the current file you are editing
Ctrl + g  // shows line number and file status



Text Editing
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a - append at the end of the cursor
A - append at the end of the line
i - insert before the cursor
I - insert at the beginning of the line
o - Open a new line below
O - open a new line above the current line


All above commands switch the file to insert mode

r - change the current character and be in command mode
s - change the current character and switch to insert mode
cc - delete the current line and switch to insert mode for editing
cw - Edit the current word
c$ - Delete from current position to end of line and keep editing
c^ - Delete all from beginning of the line to current location and keep editing


x - deletes the current character e.g - 5x to delete 5 character
dd - deletes the current line - e.g - 5dd to delete 5 lines
dw - deletes the current word
de - deletes till the end of current word including a whitespace
d^ - deletes from beginning of the line to current caret position
d$ - deletes from current caret position to end of the line (Shift + d does the same)

R - enters to overwrite mode. Whatever character you type will replace the character under the caret
~ - Changes the case of the character under the caret
J - join the next line to the current line