Posts in the “linux-unix” category

vi/vim FAQ: How do I show hidden characters in the vi/vim editor?

Solution

I just learned that you can show hidden characters like tabs and end-of-line/newline characters in vi/vim with its set list command. Just go into last-line mode with the : character, then use that command:

:set list

When I do that in my current file, the $ is used to show newline characters, and TAB characters show up as ^I:

#!/bin/sh$
exec scala "$0" "$@"$
!#$
$
println("Hello, world")$
$
^I// tab test$
$
$

If you ever need to show hidden/invisible characters in vi/vim, I hope this is helpful.

I’ve been working a lot on the next generation web server for the alvinalexander.com website lately, and as I’m looking at different HTTP accelerators, I keep wanting/needing to look at the headers returned by my web pages. A simple way to look at the HTTP headers from the command line is with the curl command, like this:

curl -I http://example.com/

Running this command against the main Google website, I see output like this:

vim quit/save/exit FAQ: How do I quit/exit vim?

Answer: This depends by what you mean by the word exit. Here's a short list of the different ways I normally quit or exit a vi/vim editor session.

vi exit - no changes made to your file (vim quit command)

If you haven't made any changes to your file you can just quit your vi (or vim) editing session like this:

vim editor syntax faq: How do I turn on (enable) or turn off (disable) vim syntax highlighting?

Short answer

Turning on syntax highlighting in your vim editor is usually fairly simple; you just need to issue a syntax on command, either in your current editor session, or in your vimrc configuration file. Here are a couple of quick examples.

vi (vim) line navigation FAQ: What is the vi command to move to the end of the current line? (How do I move to the end of the current line in vim?)

Short answer: When in vi/vim command mode, use the "$" character to move to the end of the current line.

Other vi/vim line related commands

While I'm in the vi line neighborhood, here's a longer answer, with a list of "vi/vim go to line" commands:

vi/vim editor FAQ: How do I undo and redo changes in the vi and vim editors?

Solution

The solutions are:

• Undo changes in vim with the u command in command mode
• redo changes using the [Ctrl][r] keystroke

See below for more details.

vim undo (how to undo a change in vi/vim)

You “undo” changes in vi and vim with the undo command, which is the u key when you are in vim command mode. For instance, if you start with this text in your editor:

Some times when you're editing a file with really long lines it's easier to work with the file if the lines don't wrap on screen. That's usually when I use the "no wrap" feature of the vi (or vim) editor.

If you don't want the lines to wrap in vi just type this command:

:set nowrap

That command tells vi not to wrap the lines. The result is that any line that was wrapped before will now scroll off the screen to the right. If you want to return it to the default wrapping mode just type this command:

Linux “open files” FAQ: Can you share some examples of how to show “open files” on a Linux system (i.e., how to use the lsof command)?

The Linux lsof command lists information about files that are open by processes running on the system. (The lsof command itself stands for “list of open files.”) In this brief article I’ll just share some lsof command examples. If you have any questions, just let me know.

Linux crontab FAQ: How do I edit my Unix/Linux crontab file?

I was working with an experienced Linux sysadmin a few days ago, and when we needed to make a change to the root user crontab file, I was really surprised to watch him cd to the root user’s cron folder, make changes to the file, then do a kill -HUP on the crontab process.

Thinking he knew something I didn’t know, I asked him why he did all of that work instead of just entering this:

In an earlier vim color configuration tutorial I described how to have fine-grained control of your vim color settings. In this article I’ll take an easier route, and show how you can use existing color schemes in your vim editor sessions.

Unix/Linux FAQ: How can I print columns of data from text files on Unix/Linux systems?

Background

One of my favorite ways to use the Unix awk command is to print columns of data from text files, including printing columns in a different order than they are in in the text file. Here are some examples of how awk works in this use case.

As a brief note today, I was recently looking for all Messages/iMessage files that are stored on my Mac, and I used this shell script to copy all of those files — many of which have the same name — into a directory named tmpdir, giving them all new names during the copy process:

# WARNING: back up your files before running this script.
#          if something is wrong, you may lose them all.
count=1
for i in `cat myfiles`
do
    fname=`basename $i`
    cp $i tmpdir/${count}-${fname}
    count=`expr $count + 1`
done

The Linux find command is used to locate files and directories based on a wide variety of criteria. I'll try to cover the most common find examples here.

Basic find command examples

To find a file or directory named "foo" somewhere below your current directory use a find command like this:

find . -name foo

If the filename begins with "foo" but you can't remember the rest of it, you can use a wildcard character like this:

Linux shell script test syntax

All of the shell script tests that follow should be performed between the bracket characters [ and ], like this:

if [ true ]
then
  # do something here
fi

Very important: Make sure you leave spaces around the bracket characters.

I'll show more detailed tests as we go along.

Linux shell file-related tests

To perform tests on files use the following comparison operators:

vim search FAQ: How do I search in vim?

There are a few commands you can use to search in the vi or vim editors. The main thing to remember is that the '/' key lets you search forward in a file, and the '?' key lets you search backwards in a file for whatever text you are looking for.

vi/vim FAQ: How can I remove control-m ^M characters in a text file using vi or vim?

“DOS format” message in vim

If you’ve ever opened a text file with vi (or vim) and saw a message on the bottom of the screen that says “dos” or “dos format”, there’s a reason for this. The file was probably created on a DOS or Windows computer, and it contains extra binary characters that are not normally found in a file created on a Unix or Linux system.

vim copy and paste FAQ: How do I copy and paste in vim (the vi or vim editor)?

In this short vi/vim tutorial I thought I'd share the most common vim copy and paste commands I use on a daily basis. I've been using vi (and vim) for almost 20 years now (wow), and these are the most common copy/paste commands I use.

The vi editor can be a little difficult to learn, so I've been writing some vi tutorials here recently. One of the first things to know about vi is that it typically functions in three different modes:

1. Command mode
2. Insert mode
3. Last line mode

Here's a quick description of each vi mode.

If you ever need to use the Unix/Linux sed command to insert text before or after a line of text in an existing file, here's how I just ran several sed commands to update my old Function Point Analysis tutorial to have a format that doesn't look like it was created in the 1990s.

This tutorial consists of over 40 files, and I had eight changes I wanted to make each file. So I had two choices: modify each file by hand over the next six hours, or run a series of sed commands and be done in 30 minutes. (I chose the sed commands.)

tar extract FAQ: How do I extract one file (or multiple files) from a tar archive without extracting the entire archive (i.e., how do I un-tar files from a tar archive)?