ZEGETECH

Writing the same long command can be quite tiresome when working in the Unix/Linux/MacOs terminal. Especially to those of us who need to do it time and again. Shortcuts are great. You get there, but way faster than the long route. And same with these bash commands. You can increase your speed in terminal usage and preserve your brain cells by keeping in mind simplified, alternative, shortcut commands. Bash aliases make this possible, increasing your workflows speed and ease while using terminal.

Introduction

Let’s look at some commands below

docker-compose up
sudo apt-get update
npm install --save angular

Every developer, sysadmin and dev-ops engineer interact daily and repeatedly with these commands in their day to day work. It’s tiresome to write these commands every time we need them. Is there a simple way?.

What if I tell you can use

cup

Instead of

docker-compose up

Yes it’s possible… meet bash Alias

What is Bash Alias?

A Bash alias is a method of supplementing or overriding Bash commands with new ones. Bash aliases make it easy for users to customize their experience in a POSIX terminal, which you definitely have is running Mac or Linux.

How to implement Aliases

By default, most Unix based Operating systems like Linux and MacOs ships with some common aliases. To list these default aliases in your system, head to your terminal and type alias then press enter. For example below is a list of default aliases in ubuntu 18.

alias egrep='egrep --color=auto'
alias fgrep='fgrep --color=auto'
alias grep='grep --color=auto'
alias l='ls -CF'
alias la='ls -A'
alias ll='ls -alF'
alias ls='ls --color=auto'

If you look keenly you will notice a common pattern.

alias alias_name='command_to_run'

And that’s how simply we implement aliases.

Where to write aliases

Aliases are often defined in a bash sourced(run when terminal starts) file such as $HOME/.bash_profile, $HOME/.profile or $HOME/.bashrc. However to organise them, we put them in a dedicated file $HOME/.bash_aliases and load this file in the bash sourced file. To do so create the file and add your aliases

touch ~/.bash_aliases

The $HOME/.bash_aliases must be loaded in your $HOME/.bashrc. Most distributions load it by default but its good to confirm. Below command will load the file.

if [ -f ~/.bash_aliases ]; then
  . ~/.bash_aliases
fi

Loading alias

After writing your alias in ~/.bash_aliases you can make them load and usable in your bash session system by reloading ~/.bashrc with below command.

 source ~/.bashrc

Unsetting alias

If you want to get rid of any alias, use unalias command

unalias ll

You can also just remove it from ~/.bash_aliases if defined there and then reload ~/.bashrc

Alias Examples

1. Update your system

    alias update='sudo apt-get update && sudo apt-get upgrade'
   

   Now if you want to update your system just run update and everything works. You can also chain it with other commands e.g to install a package

    update && apt-get install vim
   

2. NPM install packages

    alias nis='npm install --save'
   

   When for example you want to install angular the command is nis angular.

3. Get your IP

    alias myip="curl http://ipecho.net/plain; echo"
   

You could alias sudo command to please for better experience in your system. e.g. please shutdown

Limitations of Aliases

1. Aliases can only be used with simple text replacements, no arguments/parameters.
2. Similar named aliases cannot co-exist.
3. Aliases cannot be (un)set in subshells or non-interactive environments.
4. Aliases take time since shell has to interpret them all before showing you prompt.

The limitation of aliases not accepting parameters can be solved by the use of bash functions.

Bash Functions

A bash function, like in any other programming language, is a set of commands that can be called within an execution sequence. Unlike aliases, bash function can accept parameters.

Functions Declaration

Function name followed by parenthesis.preffered

#!/bin/bash
function_name {
  command
}

Or using function keyword.

#!/bin/bash
function function_name {
  command
}

Function Parameters

To pass any number of arguments to the bash function, simply put them right after the function’s name, separated by a space. It is a good practice to double-quote the arguments to avoid the misparsing of an argument with spaces in it.

The passed parameters are available in the function as an array of parameters, i.e. $1, $2, $3 … $n, corresponding to the position of the parameter after the function’s name

Example

#!/bin/bash
greeting() {
  echo "Hello $1"
}

You can call function greeting with argument

greeting "John"
# Output
Hello John

Bash Functions Examples

1. Kill Processes The function will kill a process by name eg kp "firefox"

   kp () {
     ps aux | grep $1 > /dev/null
     mypid=$(pidof $1)
     if [ "$mypid" != "" ]; then
       kill -9 $(pidof $1)
       if [[ "$?" == "0" ]]; then
         echo "PID $mypid ($1) killed."
       fi
     else
       echo "None killed."
     fi
     return;
   }
   

2. Uptime Displays system uptime.

    myuptime () {
      uptime | awk '{ print "Uptime:", $3, $4, $5 }' | sed 's/,//g'
      return;
    }
   

   Displays system uptime.

3. Tar and Compress Compress a folder ie targz test

    targz() { tar -zcvf $1.tar.gz $1; rm -r $1; }
    # extra .tar.gz
    untargz() { tar -zxvf $1; rm -r $1; }
   

   We have compiled a list of commonly used aliases that you can install and get started easily. Check the github repo.

Conclusion

Hopefully, this guide has given you some inspiration for creating your aliases and bash functions. Extensive use of these can help make your time in the shell more enjoyable and less complex.