Command-Line Vim

Before anybody says anything, I know this can often be better accomplished using sed, perl, <your favorite tool>. That said, you can use any command in the ex toolbox directly from the command-line without actually opening Vim. Any argument preceeding the filename to be edited that begins with a plus symbol (+) is taken as an ex-command. Alternatively, you can use the -c command line flag to indicate an ex-command is being specified. This has two handy uses. For one, you can pre-process a file with an ex-command before it's loaded into Vim. Secondly, you can use Vim in a script non-interactively. For example:

travis@travis-ubuntu:/home/travis% echo "hello world" > fun.txt
travis@travis-ubuntu:/home/travis% vim "+s/hello/goodbye cruel/" "+wq" fun.txt
travis@travis-ubuntu:/home/travis% cat fun.txt
goodbye cruel world

You could get an identical result with:

vim -c "s/hello/goodbye cruel/" -c "wq" fun.txt

As an aside, this is the 100th post to Daily Vim. I want to thank everyone who's contributed to the blog so far and made this a great learning experience. You guys have made this a really fun project, so keep the comments coming!

MySQL Pager = Vim

When using MySQL, you can set any pager you wish using the pager command.

mysq> pager less
PAGER set to 'less'

Using Vim as your pager allows you to quickly munge query output into whatever format you want.

mysql> pager vim -
PAGER set to 'vim -'

Thanks to Jay for the tip!

Grep For a Column

Sometimes when using MySQL, you need to know every table that contains a given column name. In the past I've accomplished this with a short script, but I've come to find out that you can simply use a SQL statement instead.

SELECT table_name FROM information_schema.COLUMNS WHERE table_schema='my_db' AND column_name='MyColumn';

Apache MaxClients

This isn't an exact science, but assuming you're using pre-fork and not MPM inside Apache 2, you should be able to estimate your MaxClients setting using the following strategy.

1) calculate average RSS usage for apache

Do a ps -ylC httpd and average the RSS column using a spreadsheet or command-line trickery. This gives you the average memory size of your Apache children.

2) apply the following formula

(server RAM * MEM percent dedicated) / average RSS usage

Given a server with 10 Gigs of RAM with 80% dedicated to Apache and an average RSS size of 20 megs, and using Google as a calculator:

(10 gigabytes * .80) / (20 megabytes) = 409.6 connections

From there, you could set MaxClients to roughly 400 connections and monitor resource usage. As always, peak load performance must be taken into account as well. Like I said, it's not an exact science; rather, a simple strategy for establishing a baseline value.

Quick Redraw

You can use z. in Vim to quickly redraw the current cursor line at the center of the window. zt redraws at the top and zb redraws at the bottom. Thanks to Nate for the tip!

Pushd + Popd

Although pushd and popd are intended mainly for programming, they fill a nice niche when navigating directory structures. If you're current working directory is some deeply nested location like /home/travis/src/myprojects/vim-patch/includes and you need to cd into /tmp for a bit but know you'll be coming back to the original directory, you should use pushd rather than cd. pushd takes the current directory and pushes it into a stack. popd pops the top directory off the stack and does an automatic cd into it. For example:

travis@travis-ubuntu:/usr/share/vim/vim71/colors% pushd /tmp
/tmp /usr/share/vim/vim71/colors
travis@travis-ubuntu:/tmp% popd
/usr/share/vim/vim71/colors
travis@travis-ubuntu:/usr/share/vim/vim71/colors%

Text Formatting Features

A friend of mine contributed the following tip. I was going to rewrite it, but he explained it very clearly, so here it is verbatim:

I've been editing a plain text latex input file and am using vim's text formatting features for the first time. First useful item is :set textwidth=80 (or your preferred column width) which auto-wraps lines as you type. This is great, unless you edit part of the file before the end and mess up the text width. I discovered through the glorious vim help system the normal command gq which auto-formats a range of text. Its default behavior is a bit weird if you use it on the whole file (like gg=G for auto-indenting code), but you can do nifty things like:

format the current paragraph: {V}gq ( { = go to previous white-space-only line V=visual line select }=go to next white-space-only line )

here's how to apply formatting to all "paragraphs" using the :global command:

:%g/^\s*$\n\s*[A-Za-z]/normal V}gq

This is really specific to LaTeX, since "paragraphs" are divided by white space lines. This pattern will match any whitespace-only line, followed by a line starting with (possibly) whitespace, then an [A-Za-z].

Thanks Chris for the great tip!