Terminals Are Sexy

Terminals are sexy is aĀ curated list of Terminal frameworks, plugins & resources for CLI lovers. Ā There is plenty of links to applications, plugins and configurations. Ā For me personally, the most useful one was the link to sensible Bash configuration.

Defensive BASH Programming

If you write any Bash code that lasts more than a day, you should definitely read “Defensive BASH Programming” and follow the advice, if you haven’t already. Ā It covers the following:

  • Immutable global variables
  • Everything is local
  • main()
  • Everything is a function
  • Debugging functions
  • Code clarity
  • Each line does just one thing
  • Printing usage
  • Command line arguments
  • Unit Testing

All that with code examples and explanation of importance.

 

dotfiles – your unofficial guide to dotfiles on GitHub

Warning: you will lose a lot of sleep if you follow the link below. :)

No matter how well you know Vim, bash, git, and a whole slew of other command line tools, I promise you, you’ll find something new, something you had no idea existed, something that will help you save hours and hours of your life by shaving off a few seconds here and there on the tasks you perform on a daily basis, in the repositories link to from this site.

I think I’ve spent most of my Sunday there and my dotfiles are so different now that I’m not sure I should commit and push them all in one go. Ā I think I might need to get used to the changes first.

Some of the things that I’ve found for myself:

  • PHP Integration environment for Vim (spf13/PIV).
  • myrepos –Ā provides a mr command, which is a tool to manage all your version control repositories.
  • bash-it – a community Bash framework.
  • Awesome dotfiles – a curated list of dotfiles resources.

… and a whole lot of snippets, tips, and tricks.

P.S.: Make sure you don’t spend too much time on these things though :)

Shell parameter expansion : default values for shell script parameters

When writing shell scripts, it’s often useful to accept some command line parameters. Ā It’s even more useful to have some defaults for those parameters. Ā Until now I’ve been using if statements to check if the parameter was empty, and if it was, to set it to the default value. Ā Something like this:

#!/bin/bash

DB_HOST=$1
DB_NAME=$2
DB_USER=$3
DB_PASS=$4

if [ -z "$DB_HOST" ]
then
    DB_HOST="localhost"
fi

if [ -z "$DB_NAME" ]
then
    DB_NAME="wordpress"
fi

if [ -z "$DB_USER" ]
then
    DB_USER="root"
fi

echo "Connecting to the database:"
echo "Host: $DB_HOST"
echo "Name: $DB_NAME"
echo "User: $DB_USER"
echo "Pass: $DB_PASS"

It turns out there is a much more elegant way to do this with shell parameter expansion. Ā Here is how it looks rewritten:

#!/bin/bash

DB_HOST=${1-localhost}
DB_NAME=${2-wordpress}
DB_USER=${3-root}
DB_PASS=$4

echo "Connecting to the database:"
echo "Host: $DB_HOST"
echo "Name: $DB_NAME"
echo "User: $DB_USER"
echo "Pass: $DB_PASS"

This is so much better. Not only the script itself is shorter, but it’s also much more obvious what is going on. Ā Copy-paste errors are much less likely to happen here too.

I wish I learned about this sooner.

Troubleshooting with /dev/tcp and /dev/udp

Imagine you are on a freshly installed Linux machine with the minimal set of packages, and you need to test network connectivity. Ā You don’t have netcat, telnet, and your other usual tools. Ā For the sake of the example, imagine that even curl and wget are missing. Ā What do you do?

Well, apparently, there is a way to do this with plain old bash. Ā A way, which I didn’t know until today. Ā You can do this with /dev/tcp and /dev/udp. Here is an example verbatim from the Advanced Bash-Scripting Guide:

#!/bin/bash
# dev-tcp.sh: /dev/tcp redirection to check Internet connection.

# Script by Troy Engel.
# Used with permission.
 
TCP_HOST=news-15.net       # A known spam-friendly ISP.
TCP_PORT=80                # Port 80 is http.
  
# Try to connect. (Somewhat similar to a 'ping' . . .) 
echo "HEAD / HTTP/1.0" >/dev/tcp/${TCP_HOST}/${TCP_PORT}
MYEXIT=$?

: <<EXPLANATION If bash was compiled with --enable-net-redirections, it has the capability of using a special character device for both TCP and UDP redirections. These redirections are used identically as STDIN/STDOUT/STDERR. The device entries are 30,36 for /dev/tcp: mknod /dev/tcp c 30 36 >From the bash reference:
/dev/tcp/host/port
    If host is a valid hostname or Internet address, and port is an integer
port number or service name, Bash attempts to open a TCP connection to the
corresponding socket.
EXPLANATION

   
if [ "X$MYEXIT" = "X0" ]; then
  echo "Connection successful. Exit code: $MYEXIT"
else
  echo "Connection unsuccessful. Exit code: $MYEXIT"
fi

exit $MYEXIT