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hello and welcome to another video we're going to be talking about shells today so bash sh leash Etc and why some of the commands that you type into your terminal are actually shell built-ins and not actual executables uh we talked about CD and why it has to be a shell built-in but I'm specifically talking about uh commands that are also provided as executables things like Echo true false a left square bracket and others so anyway let's jump into it so in order to show this first I wanted to show you some of some examples of these commands that are present in multiple places so for instance the square bracket command uh is both a Shell built in and if we were to run it it's actually an executable as well and you'll see that they almost report the same this one actually says bash here so it's giving you a hint that this is not the uh Bin square bracket the same is true for things like test and true and false these are also provided as bin tests been true bin Falls there's also Echo is another example of this so if we do type Echo it's going to be a shell built-in anyway there's a whole bunch of these uh shell built-ins that are also present as commands and they all function mostly the same there's a few that don't uh kill is one of the ones which uh is pretty different so for instance we do help for bin kill versus kill Dash help you'll see that they have a slight different set of options and the the shell one is slightly different than the one that's in bin uh there's a few others that differ slightly but they're mostly in line with each other now the main reason for making things a Shell built in versus an executable comes down to Performance and that is that starting an executable is relatively slow to just parsing a command and Performing the side effect within the process uh the easiest way to show this is with the time built in um for instance if you do time true you'll see that it's always going to be essentially zero zero zero zero whereas if we're running bin true you'll see that it's often taking some non-zero amount of time and while this doesn't feel like a lot yeah it's you know one thousandth of a second uh every time that you're using true uh this adds up a lot in Shell scripts and so it tends to do stuff directly within bash without having to create a process execute that process wait for that process to finish and look at its exit code and all that other stuff so we can just do that work directly inside the shell interpreter and not have to switch contacts into all that other stuff which is expensive you know creating process even if they're trivial like true...