Vim & Unix

Vim

Reformatting

To indent all the code, use gg=G. Then all lines will be indented according to a specific style.

Commenting Multiple Lines of Code

• Press CTRL + Q (on Windows) or CTRL + V (On Linux) to enter the VISUAL BLOCK Mode.

• Type SHIFT-I to insert in VISUAL BLOCK Mode. To comment, type // and then ESC to go back to Normal Mode . Then the text // will be inserted in front of each line selected.

• To uncomment, select // on each line that you wish to uncomment, and x to delete them.

Changing Names

Changing the name of one type/variable/method call

Occasionally, we mix up our variable or our method name, and we need to fix it before the code runs correctly or compiles. Suppose we have

double perimeter = get_area();

and we realize that we should be calling get_perimeter instead. Instead of using backspace or delete to delete the characters one by one, we can use cw to change the word get_area into get_perimeter.

To do so, (i) place the cursor at the beginning of get_area. Remember to avoid using arrow keys or h or l to move letter-by-letter. You can use w or b for faster word-by-word navigation. (ii) type cw to remove the word get_area and enter INSERT mode. Now type get_perimeter to replace the method name and ESC to return back to NORMAL mode.

Basically, the command we should memorize here is using cw to change one word.

Changing multiple names on the same line

Notice that this method applies to the words in one line only.

Sometimes we have multiple occurrences that we wish to change on the same line. Let's say:

int area = get_area();

and we realize that we should be calculating perimeter instead of area. One option is to use cw twice. But we could also use the substitute command, like so. Place the cursor on this line, and type :s/area/perimeter/gc, and then ENTER. Here is what it does:

• :allows us to issue a command to Vim

• s/<what to substitute>/<substitute with this>/ tells Vim what we want to replace and replace with what.

• g stands for global and it says that we want to substitute all occurrences (in this line only)

• c is optional, and it tells Vim to confirm every replacement with us.

Changing multiple occurrences in a block

If there are only a few lines and you can count the size of the scope within which you want to search and replace, you place your cursor at the beginning of the method and issue the command :.,+4s/<what to substitue>/<substitue with this>. Here . refers to the current line; , is a separator, +4 refers to the next four lines.

Suppose your cursor is far away and you have the line number turned on. Let say the method above appears at Lines 125 to 131. You can issue the command :125,131s/<what to substitute>/<substitute with this>.

Alternatively, you can use VISUAL-LINE mode. Place the cursor at the beginning of the method, and press SHIFT-V. This enters the VISUAL-LINE mode. Now, navigate to select the scope within which you want to search and replace (5j or } works in this case), and press :. You will see that the command prompt is pre-filled with :'<,'> to signify the selected range. Continue typing s/<what to substitute>/<substitute with this> and ENTER.

Changing all occurrences in a file

Let's say that you have a typo in a file, where you have named all variables angel instead of angle, and you want to fix all occurrences of this in the file. You can use % to signify that the range of substitution is the entire file.

The command :%s/angle/angle/g should replace all occurances for you.

Typing Long Variable/Function Names

Auto-completion

You can type CTRL-P or CTRL-N in INSERT mode to auto-complete a word. So you only need to type the long name the first time. Subsequently, type the prefix and auto-complete.

Abbreviation

You can set up a temporary abbreviation in your ~/.vimrc. Example

ab noc num_of_customers

After the configuration is read, you only need to type noc in your code and it will be automatically expanded to num_of_customers.

This is useful for functions from the CS1010 library, such as cs1010_println_long, as well.

Fixing Mistakes

Undo and Redo

u undoes the last action. CTRL+R redoes the action.

Unix

Terminal Control Sequence

• CTRL + D: signal the end of input to a program.

• CTRL + Z: suspend the current running program.

• CTRL + C: terminate the current running program.

• CTRL + S: freeze the terminal.

• CTRL + Q: resume the terminal.

Note that often hitting CTRL + Z will causing the resources not freed in time. So, try to use CTRL + C instead.

Unix Directory

For the home directory, sometimes we add the username behind ~ to indicate the home directory of the other user. E.g., ~bob means the home directory of a user named bob.

Directory-related Commands

• In Unix, a file or directory with a name that starts with . is hidden from ls. To show these files, we need to run ls with -a flag.

• Entering cd alone brings you back to your home directory.

• rmdir: ReMove a subDIRectory rmdir removes a subDIRectory in the current directory -- note that a directory must be empty before it can be removed.

File Management

• To copy a directory, we use cp -r, where -r stands for copying recursively.

• The cp command takes in two arguments, the first is the source, the second is the destination.

• Same as the cp command, the mv command takes in two arguments also. THe first one is source and the second one is destination.

• rm -rf, -r means recursively, -f means force.

• cat: CATenate file content to screen This command is used to take a look at the content of the file. If the file is too long, we can use the variant of cat, called less. In less, we use <space> to move down one page, b to move Back up one page and q to quit. And if not argument is specified, cat will use the standard input (keyboard) as its input. And in this case, remember to use CTRL + D to signal the end of the input.

• man: MANual Just use man <name of command> to see the manual of that command.

File Permission Management

The What of File Permissions

r is read, w is write, x is execute. And the permissions on a file can be expressed in two ways:

1. using symbolic notation. For instance, rwx, r-x, -wx, where a - means that the corresponding permission is not given (in the order of r, w, x)

2. using a numerical notation. This notation uses a digit between 0 to 7, which is computed as a sum of individual digit representing the permissions: r is represented with 4, w is represented with 2, and x is represented with 1. For instance, r-x has a numerical representation of 5(4+1), and -wx has a numerical representation of 3(2+1). And the max is 7(4+2+1).

The Who of File Permissions

Unix divides the users into three classes: u is the user who owns the file; g refers to the users in the same group as the user; and o are all the other users. The permission can be controlled separately for these classes of users. The permission notation simply concatenates the file permissions of each class of users together, in the order of u, g and o. For instance, the permission of 644, or rw-r--r--, on a file means that:

• the owner can read and write

• the group users can only read

• all the other users can only read Sometimes you may see d in front of the permission, that means it is a directory.

Standard Input/Output

Output Redirection

The operators > and >> are used to redirect the standard output to a file. The difference is that > will overwrite the given file, while >> will concatenate into the given file.

Input Redirection

The operatros < is used to redirect a file into the standard input. So, instead of reading from the keyboard, we can now read from a file. For example, wc test.txt is the same with wc < test.txt. A slight difference is that the second one will have no file name.

In most CS programming assignments, however, to keep things simple, you will be asked to read from the standard input only, so the < is a great-time-saver -- you do not have to repeatedly type in the same input data over and over from the keyboard. You can just save the input data in a file, then redirect it to standard input with the < operator.

Advanced

Composing Programs with |

The | operator takes the standard output from one program and redirects it as the standard input of another program. For example

$ cat test.txt | wc
    1   11  64

and this command is just the same as

$ wc < test.txt

Another example that shows the power of | is that suppose we have three files and we want to count the total number of lines, words and characters in these three files. We can use one line of command to achieve this,

cat test.txt foo.txt bar.txt | wc
    3   33  192

Some other commands

• echo simply prints out the command-line argument to the standard output (terminal)

$ echo "hello world!"
hello world!

• sort rearrange the input lines in alphabetical order.

• uniq remove any two consecutive lines that are the same.

• grep returns the lines of text from the given file (or the standard input) that matches the given string. For instance, run

grep abc

and start typing in some lines of text, some containing abc, some do not. grep will spew out into the standard output all the lines that contain the text abc somewhere. As usual, hit CTRL + D when you are done. To grep a pattern in a directory, use grep -r <pattern> <directory>

See the famous pipe example example from CS1010.

Notice that the wc -l means we only want to print the number of lines to our standard output.

Pattern matching in bash

Pattern	Matches
*	0 or more characters
?	One character
[..]	One character, coming from the given set between [ and ], - to indicate a range.
{.., ..}	Either one of the names, separated by ,.

Example 1, ls [f-t]*t matches all file names that start with the alphabet f, g, etc, until t, followed by zero or more characters, followed by t.

Example 2, ls {fo,ba}??txt matches any file names that start with either fo or ba, followed by two characters, followed by txt.

Credit

1. CS1010 Handbook - Vim Common Operations

2. CS1010 Handbook - Unix Background

3. CS1010 Handbook - Unix Essentials

4. CS1010 Handbook - Unix Advanced