One of the most useful commands is the i (insert) command. After you type i, everything you type until you hit ESC is inserted into the file. Try this now; position yourself to some word in the file and try inserting text before this word. If you are on an dumb terminal it will seem, for a minute, that some of the characters in your line have been overwritten, but they will reappear when you hit ESC.
Now try finding a word which can, but does not, end in an `s'. Position yourself at this word and type e (move to end of word), then a for append and then `sESC' to terminate the textual insert. This sequence of commands can be used to easily pluralize a word.
Try inserting and appending a few times to make sure you understand how this works; i placing text to the left of the cursor, a to the right.
It is often the case that you want to add new lines to the file you are editing, before or after some specific line in the file. Find a line where this makes sense and then give the command o to create a new line after the line you are on, or the command O to create a new line before the line you are on. After you create a new line in this way, text you type up to an ESC is inserted on the new line.
Many related editor commands are invoked by the same letter key and differ only in that one is given by a lower case key and the other is given by an upper case key. In these cases, the upper case key often differs from the lower case key in its sense of direction, with the upper case key working backward and/or up, while the lower case key moves forward and/or down.
Whenever you are typing in text, you can give many lines of input or just a few characters. To type in more than one line of text, hit a RETURN at the middle of your input. A new line will be created for text, and you can continue to type. If you are on a slow and dumb terminal the editor may choose to wait to redraw the tail of the screen, and will let you type over the existing screen lines. This avoids the lengthy delay which would occur if the editor attempted to keep the tail of the screen always up to date. The tail of the screen will be fixed up, and the missing lines will reappear, when you hit ESC.
While you are inserting new text, you can use the characters you normally use at the system command level (usually ^H or #) to backspace over the last character which you typed, and the character which you use to kill input lines (usually @, ^X, or ^U) to erase the input you have typed on the current line.** The character ^W will erase a whole word and leave you after the space after the previous word; it is useful for quickly backing up in an insert.
Notice that when you backspace during an insertion the characters you backspace over are not erased; the cursor moves backwards, and the characters remain on the display. This is often useful if you are planning to type in something similar. In any case the characters disappear when when you hit ESC; if you want to get rid of them immediately, hit an ESC and then a again.
Notice also that you can't erase characters which you didn't insert, and that
you can't backspace around the end of a line. If you need to back up
to the previous line to make a correction, just hit ESC and move
the cursor back to the previous line. After making the correction you
can return to where you were and use the insert or append command again.
You can make small corrections in existing text quite easily. Find a single character which is wrong or just pick any character. Use the arrow keys to find the character, or get near the character with the word motion keys and then either backspace (hit the BS key or ^H or even just h) or SPACE (using the space bar) until the cursor is on the character which is wrong. If the character is not needed then hit the x key; this deletes the character from the file. It is analogous to the way you x out characters when you make mistakes on a typewriter (except it's not as messy).
If the character is incorrect, you can replace it with the correct character by giving the command rc, where c is replaced by the correct character. Finally if the character which is incorrect should be replaced by more than one character, give the command s which substitutes a string of characters, ending with ESC, for it. If there are a small number of characters which are wrong you can precede s with a count of the number of characters to be replaced. Counts are also useful with x to specify the number of characters to be deleted.
You already know almost enough to make changes at a higher level. All you need to know now is that the d key acts as a delete operator. Try the command dw to delete a word. Try hitting . a few times. Notice that this repeats the effect of the dw. The command . repeats the last command which made a change. You can remember it by analogy with an ellipsis `...'.
Now try db. This deletes a word backwards, namely the preceding word. Try dSPACE. This deletes a single character, and is equivalent to the x command.
Another very useful operator is
or change. The command
thus changes the text of a single word.
You follow it by the replacement text ending with an ESC.
Find a word which you can change to another, and try this
Notice that the end of the text to be changed was marked with the character
`$' so that you can see this as you are typing in the new material.
It is often the case that you want to operate on lines. Find a line which you want to delete, and type dd, the d operator twice. This will delete the line. If you are on a dumb terminal, the editor may just erase the line on the screen, replacing it with a line with only an @ on it. This line does not correspond to any line in your file, but only acts as a place holder. It helps to avoid a lengthy redraw of the rest of the screen which would be necessary to close up the hole created by the deletion on a terminal without a delete line capability.
Try repeating the c operator twice; this will change a whole line, erasing its previous contents and replacing them with text you type up to an ESC.**
You can delete or change more than one line by preceding the dd or cc with a count, i.e. 5dd deletes 5 lines. You can also give a command like dL to delete all the lines up to and including the last line on the screen, or d3L to delete through the third from the bottom line. Try some commands like this now.* Notice that the editor lets you know when you change a large number of lines so that you can see the extent of the change. The editor will also always tell you when a change you make affects text which you cannot see.
Now suppose that the last change which you made was incorrect; you could use the insert, delete and append commands to put the correct material back. However, since it is often the case that we regret a change or make a change incorrectly, the editor provides a u (undo) command to reverse the last change which you made. Try this a few times, and give it twice in a row to notice that an u also undoes a u.
The undo command lets you reverse only a single change. After you make a number of changes to a line, you may decide that you would rather have the original state of the line back. The U command restores the current line to the state before you started changing it.
You can recover text which you delete, even if undo will not bring it back; see the section on recovering lost text below.
SPACE advance the cursor one position ^H backspace the cursor ^W erase a word during an insert erase your erase (usually ^H or #), erases a character during an insert kill your kill (usually @, ^X, or ^U), kills the insert on this line . repeats the changing command O opens and inputs new lines, above the current U undoes the changes you made to the current line a appends text after the cursor c changes the object you specify to the following text d deletes the object you specify i inserts text before the cursor o opens and inputs new lines, below the current u undoes the last change