Vi and Vim Autocommand: 3 Steps to Add Custom Header To Your File Automatically

 In this article, using 3 simple steps, let us review how to use this powerful autocmd feature of Vim to create a header section inside a file (for example, header in a C programming code) with file name, creation date, last modified date/time automatically populated when you open a file in vi.

Vim autocmd syntax:

autocmd  {event} {pattern} {cmd}

Events: There are more than 40 autocmd events. Following are few sample autocmd events.

BufNewFile	- Starting to edit a file that doesn't exist.
FileReadPre	- Before reading a file with a ":read" command.
BufWritePre	- Starting to write the whole buffer to a file.
FileWritePre	- Starting to write part of a buffer to a file.
BufDelete	- Before deleting a buffer from the buffer list.
BufWipeout	- Before completely deleting a buffer.
BufNew	- Just after creating a new buffer.
BufEnter	- After entering a buffer.
BufLeave	- Before leaving to another buffer.
SwapExists	- Detected an existing swap file.

Most of the developers want some default header for their programs. Lets take an example. When opening a “.c” file, you need a file header which has author, filename etc.. Consider that I need the following template to be loaded automatically while opening a new “.c” file. You can achieve this in three steps as mentioned below.

/* -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.

* File Name : 1.c

* Purpose :

* Creation Date : 22-12-2008

* Last Modified : Mon 22 Dec 2008 10:36:49 PM PST

* Created By :  

_._._._._._._._._._._._._._._._._._._._._.*/

Step 1: Create a template file

Save the above template in a text file with “:insert” in the first line, followed by the template and a “.”(dot) in the last line as shown below.

$ cat c_header.txt
:insert
/* -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.

* File Name :

* Purpose :

* Creation Date :

* Last Modified :

* Created By :  

_._._._._._._._._._._._._._._._._._._._._.*/
.

Step 2: Add autocmd commands to ~/.vimrc

Add the following lines in the ~/.vimrc file.

$ cat ~/.vimrc
autocmd bufnewfile *.c so /home/jsmith/c_header.txt
autocmd bufnewfile *.c exe "1," . 10 . "g/File Name :.*/s//File Name : " .expand("%")
autocmd bufnewfile *.c exe "1," . 10 . "g/Creation Date :.*/s//Creation Date : " .strftime("%d-%m-%Y")
autocmd Bufwritepre,filewritepre *.c execute "normal ma"
autocmd Bufwritepre,filewritepre *.c exe "1," . 10 . "g/Last Modified :.*/s/Last Modified :.*/Last Modified : " .strftime("%c")
autocmd bufwritepost,filewritepost *.c execute "normal `a"

Step 3: Create a new *.c file with automatic header

Now, when you create a new *.c file using vim, this will automatically add the header defined in the Step1 and populate the File Name and Creation Date automatically as shown below.

$ vi myfile.c
/* -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.

* File Name : myfile.c

* Purpose :

* Creation Date : 20-12-2008

* Last Modified :

* Created By :

_._._._._._._._._._._._._._._._._._._._._.*/

When you save the myfile.c file, it will automatically update the Last Modified field accordingly as shown below.

$ vi myfile.c
/* -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.

* File Name : myfile.c

* Purpose :

* Creation Date : 20-12-2008

* Last Modified : Sat 20 Dec 2008 09:37:30 AM PST

* Created By :

_._._._._._._._._._._._._._._._._._._._._.*/

Explanation of the autocmd commands inside ~/.vimrc

$ cat -n ~/.vimrc
     1  autocmd bufnewfile *.c so /home/jsmith/c_header.txt
     2  autocmd bufnewfile *.c exe "1," . 10 . "g/File Name :.*/s//File Name : " .expand("%")
     3  autocmd bufnewfile *.c exe "1," . 10 . "g/Creation Date :.*/s//Creation Date : " .strftime("%d-%m-%Y")
     4  autocmd Bufwritepre,filewritepre *.c execute "normal ma"

     5  autocmd Bufwritepre,filewritepre *.c exe "1," . 10 . "g/Last Modified :.*/s/Last Modified :.*/Last Modified : " .strftime("%c")
     6  autocmd bufwritepost,filewritepost *.c execute "normal `a"

• Line 1 defines the template file. This indicates that for *.c file, /home/jsmith/c_header.txt template file should be used.
• Line 2 will search for the pattern “File Name :” from the 1st line to 10th line. If found, it will write the current filename in that line.
• Line 3 will update the Creation Date field.
• Line 5 will update the Last Modified field with the current date and time when you save the file.
• Line 4 & 6: While saving the file, the cursor will move to the “Last modified :” (because of last write operation). If you want the cursor back to the previous position then, you need to add Line 4 and 6 to the .vimrc file.
• Line 4 will mark the current cursor position before updating.
• Line 6 will restore the cursor position back to its previous position.

Final Note:

• Verify whether autocmd is enabled in Vi / Vim – Execute :version from vi / vim. If autocommand feature is enabled, it will display +autocmd.
• Autocommand help – Execute :help au from vi / vim, to get quick help on vim autocmd features.