1
00:00:00,180 --> 00:00:05,160
Hello the beautiful people and welcome to this video all about file extensions in Linux.

2
00:00:05,160 --> 00:00:08,220
Now on operating systems such as Windows file extensions.

3
00:00:08,220 --> 00:00:11,490
Allow me to tell what type of file that you're dealing with at a glance.

4
00:00:11,490 --> 00:00:17,130
For example, we know that files with names ending in txt are text files and files with names ending

5
00:00:17,130 --> 00:00:23,550
in jpg or PNG are likely to be images, but in Linux, file extensions usually don't matter and the

6
00:00:23,550 --> 00:00:27,210
system tends to look at the contents of the file rather than just its name.

7
00:00:27,330 --> 00:00:30,720
But sometimes file extensions really do matter.

8
00:00:30,720 --> 00:00:36,150
So in this video, we're going to take a bit of a deep dive into understanding file extensions in Linux

9
00:00:36,150 --> 00:00:39,060
and shine some light onto their strange behavior.

10
00:00:39,060 --> 00:00:43,050
And by the end of the video, you'll know what freedoms the Linux operating system gives you when naming

11
00:00:43,050 --> 00:00:46,470
your files, what interesting things can happen, and what you need to be aware of.

12
00:00:46,500 --> 00:00:51,390
Oh, and you'll also have a new command in your toolkit that will help you when dealing with files on

13
00:00:51,390 --> 00:00:52,320
your file system.

14
00:00:52,320 --> 00:00:54,600
So this is all very useful stuff, very exciting stuff.

15
00:00:54,600 --> 00:00:56,880
Let's go ahead and jump right into it.

16
00:00:57,610 --> 00:00:58,120
All right.

17
00:00:58,120 --> 00:01:00,850
So I've gone ahead and put some files here on my desktop.

18
00:01:00,880 --> 00:01:06,640
First of all, I've got an image of Tux, the traditional Penguin logo for Linux here in P and G format.

19
00:01:06,670 --> 00:01:11,830
Now, Tux, in case you're interested, is short for the word tuxedo, which is a fancy type of black

20
00:01:11,830 --> 00:01:16,720
and white suit, usually worn by waiters and partially dressed people at high class parties.

21
00:01:16,750 --> 00:01:21,040
Now penguins are said to look like they're wearing little tuxedos because of their black and white coloring.

22
00:01:21,040 --> 00:01:25,090
And that's where Tux gets his name from the word tuxedo, in case you were interested.

23
00:01:25,090 --> 00:01:30,340
But besides a picture of of the lovely tux here and random trivia, I've also got a text file here with

24
00:01:30,340 --> 00:01:33,130
some Shakespeare in it called Shakespeare Text.

25
00:01:33,130 --> 00:01:37,150
And I also have a spreadsheet file with some random numbers in it.

26
00:01:37,600 --> 00:01:44,820
So let's go ahead and take a look at the file command to see how Linux handles file types.

27
00:01:44,830 --> 00:01:49,810
So if I go ahead and open a terminal using the control alternate keyboard shortcut and just drag it

28
00:01:49,810 --> 00:01:51,820
a bit out of the way so we can still see the files.

29
00:01:52,240 --> 00:01:55,580
I'm going to introduce you to a new command called the File Command.

30
00:01:55,600 --> 00:02:00,430
Now, the file command will tell us basically what type of file that we are dealing with.

31
00:02:00,460 --> 00:02:07,930
So, for example, if we try to have a look at tux here, if we do file tux PNG, we actually need to

32
00:02:07,930 --> 00:02:09,280
go to our desktop first.

33
00:02:09,280 --> 00:02:11,230
So let's shift over to our desktop.

34
00:02:11,590 --> 00:02:14,470
Clear the screen and do file tux.

35
00:02:14,470 --> 00:02:19,720
And I can actually just just so you see, I can actually just with t you go ahead and press tab and

36
00:02:19,720 --> 00:02:21,850
it will autofill that as well just showing you that tab.

37
00:02:21,850 --> 00:02:26,320
Auto completion works perfectly fine for far names, just like it does for folders.

38
00:02:26,320 --> 00:02:28,510
So it's a great, great thing that we learned in the last video.

39
00:02:28,580 --> 00:02:35,890
Okay, so let's have a look file of tux PNG and it will tell us that this is PNG image data.

40
00:02:35,890 --> 00:02:41,370
It'll tell us the size of the file and loads of other stuff as well, but it tells us the file type.

41
00:02:41,380 --> 00:02:41,950
Okay.

42
00:02:41,980 --> 00:02:54,340
Now if I rename txt png if I rename this to tux dot jpg, which is another type of image file, you

43
00:02:54,340 --> 00:02:55,930
can see that it's been renamed there.

44
00:02:55,930 --> 00:02:57,450
But let's do that again.

45
00:02:57,730 --> 00:02:58,120
Let's try.

46
00:02:58,150 --> 00:03:01,690
File of txt jpg and let's see what happens.

47
00:03:02,740 --> 00:03:07,890
Now you can see here that it's still says that it is a p and g file.

48
00:03:07,900 --> 00:03:08,980
Now this is important.

49
00:03:08,980 --> 00:03:13,480
Point number one in Linux file extensions don't matter.

50
00:03:14,020 --> 00:03:19,960
Unlike Windows, Linux doesn't determine file type using the file extension, but instead it reads a

51
00:03:19,960 --> 00:03:22,930
piece of code inserted at the top of every file.

52
00:03:22,930 --> 00:03:28,030
And that piece of code is known as a header and it serves as a kind of label for Linux to read.

53
00:03:28,030 --> 00:03:31,480
And when Linux reads that label, it knows the file type.

54
00:03:31,480 --> 00:03:37,180
So changing just the name of the file won't make a difference because that file header won't have changed.

55
00:03:37,480 --> 00:03:41,350
Okay, so here we have some Shakespeare script in text format.

56
00:03:41,350 --> 00:03:46,690
So if I open that up, you can see that there is plenty of text in there which I just copied and pasted

57
00:03:46,990 --> 00:03:48,690
from Romeo and Juliet.

58
00:03:48,760 --> 00:03:51,570
Okay, so that's the kind of stuff that I do.

59
00:03:51,580 --> 00:03:59,350
So when we check the file type we have here, if we do file Shakespeare text, it'll tell us that it

60
00:03:59,350 --> 00:04:01,570
is an ASCII text file.

61
00:04:02,260 --> 00:04:08,770
But now if I try to turn this into a PDF, so if I rename it and try to say, okay, this is now Shakespeare

62
00:04:08,810 --> 00:04:15,310
dot PDF and I rename it now the system, it appears to have changed the icon.

63
00:04:15,310 --> 00:04:15,580
Right?

64
00:04:15,580 --> 00:04:21,970
It looks like that's a PDF file, but if I try to run the file file command again file Shakespeare dot

65
00:04:21,970 --> 00:04:27,490
pdf, it still tells us that it's ASCII text.

66
00:04:27,580 --> 00:04:35,380
So Linux read the Linux, read the header of the file and saw that it was still a text file.

67
00:04:35,410 --> 00:04:41,140
But what happens when we try to open it because it looks like the system thinks it's a PDF because you

68
00:04:41,140 --> 00:04:44,830
can see the logo is changed but it's still telling us that it's a text file.

69
00:04:44,830 --> 00:04:45,610
What's going on there?

70
00:04:45,610 --> 00:04:47,020
Why is it think it's different?

71
00:04:47,050 --> 00:04:49,090
Well, if we try to open it, what happens?

72
00:04:50,150 --> 00:04:51,650
Well, now we get an error.

73
00:04:51,920 --> 00:04:58,610
We see that the default program to open files with names ending in PDF is a PDF reader.

74
00:04:58,610 --> 00:05:03,620
And when we try to open this file in the PDF Reader, we get an error from the program as it's trying

75
00:05:03,620 --> 00:05:05,360
to open our file as a PDF file.

76
00:05:05,360 --> 00:05:13,010
And what the system basically did is say, Ah, that's a file that ends in PDF, it's probably a PDF

77
00:05:13,010 --> 00:05:17,600
file, so let me be helpful and allow the user to open it in a PDF viewer.

78
00:05:17,930 --> 00:05:24,050
Now obviously a PDF reading program isn't designed to read text files, it's designed to read PDFs,

79
00:05:24,050 --> 00:05:26,050
and that's what's causing the issue here.

80
00:05:26,060 --> 00:05:26,810
Now, this is important.

81
00:05:26,810 --> 00:05:28,490
This is an important distinction to make.

82
00:05:28,520 --> 00:05:34,580
Important point number two, although the operating system will know what file format the actual file

83
00:05:34,580 --> 00:05:40,340
is by reading the header, the extra programs that are installed on top of the operating system such

84
00:05:40,340 --> 00:05:46,370
as this PDF viewer are trying to open the files that might require certain formats or other file extensions

85
00:05:46,370 --> 00:05:47,570
in order to work.

86
00:05:47,570 --> 00:05:52,340
So what's happening is it's all this to make this automatically want to open as a PDF.

87
00:05:52,340 --> 00:05:59,660
It just saw the file name, it just looked at the file name, but the content is still text and it says

88
00:05:59,660 --> 00:06:00,920
here are file type.

89
00:06:00,920 --> 00:06:07,400
Plain text is not supported, but it got the program got tricked, it saw the file name and that's why

90
00:06:07,400 --> 00:06:09,020
it wanted to open it as a PDF.

91
00:06:09,020 --> 00:06:14,810
If I rename it back to text, just change the text, change that back.

92
00:06:14,810 --> 00:06:17,900
You'll see now that it will open fine as a text file.

93
00:06:17,900 --> 00:06:20,390
Okay, so that's the important distinction to make there.

94
00:06:20,390 --> 00:06:24,800
The programs that are installed on top of the operating system such as PDF viewers and stuff like that,

95
00:06:24,800 --> 00:06:30,890
they might need the file to have a specific file extension in order to open them, but the operating

96
00:06:30,890 --> 00:06:33,140
system itself does not care.

97
00:06:33,140 --> 00:06:34,430
So let's see this in a bit more detail.

98
00:06:34,430 --> 00:06:38,330
If I take a look at the spreadsheet here, it's called data downloads.

99
00:06:38,360 --> 00:06:46,020
If I do file of data downloads, it says that it's an ODS file which stands for open document spreadsheets.

100
00:06:46,400 --> 00:06:52,130
Okay, now this means we can open it up in LibreOffice Calc, which is basically the Linux version of

101
00:06:52,130 --> 00:06:54,710
Microsoft Excel or the Apple equivalent.

102
00:06:54,710 --> 00:06:58,850
It's like this spreadsheet program and it's got it's got a few numbers in there.

103
00:06:58,850 --> 00:06:59,350
Okay.

104
00:07:00,710 --> 00:07:08,210
But, um, now if I close the spreadsheet and rename that, for example, to a text file, so if I rename

105
00:07:08,210 --> 00:07:15,500
it to data txt rename that, you can see that now it wants to be opened up in a dot txt format.

106
00:07:16,160 --> 00:07:16,480
Okay.

107
00:07:16,610 --> 00:07:20,030
And now I try to open that up in LibreOffice Calc.

108
00:07:20,030 --> 00:07:25,520
So if I click up here, I type calc and it comes up, I click LibreOffice Calc.

109
00:07:26,430 --> 00:07:27,780
Wait for that to boot up.

110
00:07:28,350 --> 00:07:28,710
Go on.

111
00:07:28,710 --> 00:07:30,750
File open.

112
00:07:31,500 --> 00:07:33,090
Go to my desktop.

113
00:07:33,090 --> 00:07:36,890
So home and then desktop and then try to open up data like text.

114
00:07:38,340 --> 00:07:41,010
You can see now that we've got all kinds of problems happening here.

115
00:07:41,310 --> 00:07:43,860
So if I tried to just open it like that, let's try and click.

116
00:07:43,860 --> 00:07:45,770
Okay, we're going to get an error.

117
00:07:45,780 --> 00:07:46,320
Okay.

118
00:07:46,470 --> 00:07:52,410
And this is because the dot txt file extension is fooling LibreOffice Calc.

119
00:07:52,530 --> 00:07:58,250
LibreOffice Calc made the mistake of reading the file extension and trying to open the file as a dot

120
00:07:58,320 --> 00:08:00,030
text file.

121
00:08:00,600 --> 00:08:02,280
Where is the actual content?

122
00:08:02,280 --> 00:08:05,820
As we can see, here is a spreadsheet file.

123
00:08:05,820 --> 00:08:07,140
It's not a text file.

124
00:08:07,170 --> 00:08:07,510
Okay.

125
00:08:07,590 --> 00:08:15,200
But if we rename that back and we rename it so that it's data downloads now, it will open fine.

126
00:08:15,210 --> 00:08:17,250
So this is the important distinction that we need to make.

127
00:08:17,280 --> 00:08:18,280
I'm going to hammer this home.

128
00:08:18,300 --> 00:08:24,330
The file extension isn't important to the Linux operating system, but it might be important to the

129
00:08:24,330 --> 00:08:27,780
software packages that we install on top of Linux.

130
00:08:27,780 --> 00:08:33,450
So do bear in mind that don't basically don't give your file names, really weird file extensions that

131
00:08:33,450 --> 00:08:39,539
don't match their content because it might confuse third party software that is installed even though

132
00:08:39,539 --> 00:08:41,549
you don't necessarily have to.

133
00:08:41,610 --> 00:08:44,360
Okay, so let's give the spreadsheet a complete lead.

134
00:08:44,370 --> 00:08:45,180
Let's try something else.

135
00:08:45,180 --> 00:08:46,830
Let's see something quite interesting.

136
00:08:46,860 --> 00:08:50,460
Let's give the spreadsheet a completely made up file extension.

137
00:08:50,460 --> 00:08:56,850
So if I call it spreadsheet dot sublime, I'll call it spreadsheet problem.

138
00:08:58,320 --> 00:08:59,640
Now it's not interesting.

139
00:08:59,640 --> 00:09:05,250
Notice how it automatically still wants to open it up in the spreadsheet software.

140
00:09:05,310 --> 00:09:13,080
Now we notice here that we didn't fool the the the software and it still knows it's an ODS file and

141
00:09:13,080 --> 00:09:15,690
we can actually open it up if I just go ahead and double click that.

142
00:09:16,880 --> 00:09:18,680
It's going to open up perfectly.

143
00:09:18,680 --> 00:09:18,990
Fine.

144
00:09:19,010 --> 00:09:20,660
You see, we've got our data in here.

145
00:09:20,690 --> 00:09:22,370
No funny business this time.

146
00:09:22,550 --> 00:09:30,410
So why can this system, why can it open up a weird file name but not a simple one like dot txt?

147
00:09:31,040 --> 00:09:37,370
Well, the reason is the software just simply didn't recognize the dot sablan file extension, so it

148
00:09:37,370 --> 00:09:41,240
might have looked to the operating system to help determine the file type instead.

149
00:09:41,360 --> 00:09:50,960
But when we called it a dot txt file, when we actually named it directly to be txt, the software thought

150
00:09:50,960 --> 00:09:53,960
it would be a bit clever and it thought, aha, I know how to deal with this.

151
00:09:53,960 --> 00:09:57,680
And it made a little bit of a shortcut to itself and was like, I'm just going to open this automatically

152
00:09:57,680 --> 00:09:59,180
as a text file.

153
00:09:59,180 --> 00:10:05,180
But that assumption was wrong in this case because the content is a spreadsheet, we just named it txt

154
00:10:05,210 --> 00:10:10,010
and that caused the program to throw an error when it found out it wasn't a txt file after all, but

155
00:10:10,010 --> 00:10:11,330
actually was a spreadsheet.

156
00:10:11,600 --> 00:10:16,640
Now the bottom line is that you have a lot of freedom to name files, whatever you want in Linux.

157
00:10:16,640 --> 00:10:17,930
You can even call them.

158
00:10:18,320 --> 00:10:23,510
You can even give them file extensions like Dot Shibboleth, which of course you couldn't do in any

159
00:10:23,510 --> 00:10:25,220
other operating system.

160
00:10:25,910 --> 00:10:28,430
This is common for having files.

161
00:10:28,430 --> 00:10:34,190
For example, if I just try and copy and paste this, if I copy and paste this file, you know, you

162
00:10:34,190 --> 00:10:35,630
might have a backup.

163
00:10:36,560 --> 00:10:40,730
You might, for example, call one file in original so you'd say, okay, I'm going to call this one

164
00:10:40,730 --> 00:10:49,820
dot ridge, and then I'd call this one, you know, maybe I'll call another one dot back or a copy it

165
00:10:49,820 --> 00:10:54,800
and call it dot, dot, dot copy or something like that.

166
00:10:54,800 --> 00:10:55,180
Okay.

167
00:10:55,340 --> 00:10:57,980
And this is how you might name your file.

168
00:10:57,980 --> 00:11:01,640
So I'd be like, Ah, this is the original, this is the copy I can see just by looking at the file

169
00:11:01,640 --> 00:11:04,970
name without it actually affecting the way the system works.

170
00:11:05,390 --> 00:11:11,540
So this is sometimes used to allow people to read file extensions that are a lot more human readable

171
00:11:11,540 --> 00:11:15,170
than, you know, things like dot odds or dot whatever.

172
00:11:16,130 --> 00:11:20,780
But just make sure that if you name your files in such a way, don't give them file names.

173
00:11:20,780 --> 00:11:23,960
That might confuse the software that you expect to open them.

174
00:11:23,960 --> 00:11:28,040
Because not all softwares like to play ball with strange file names.

175
00:11:29,440 --> 00:11:29,830
Okay.

176
00:11:29,830 --> 00:11:33,180
So that will bring our discussion of Linux file extensions to a close.

177
00:11:33,190 --> 00:11:37,360
So as a summary of what you learn in this video, you learn that you can use the file command to know

178
00:11:37,360 --> 00:11:39,490
for sure what type of file that you're dealing with.

179
00:11:39,490 --> 00:11:43,840
And you learn that file extensions aren't important to the Linux operating system, which means you

180
00:11:43,840 --> 00:11:45,670
can name files, whatever you want.

181
00:11:45,670 --> 00:11:47,630
Yes, even dot qibla.

182
00:11:47,710 --> 00:11:52,840
But while you're doing that, make sure you try not to confuse third party software that might need

183
00:11:52,840 --> 00:11:57,640
to open the file because it might be expecting specific file extensions.

184
00:11:57,640 --> 00:12:01,720
And if you try to confuse it, then you'll just get errors in a very, very bad time.

185
00:12:01,840 --> 00:12:08,320
So coming up next in the next video, we're going to take your command line skills to a whole new level

186
00:12:08,320 --> 00:12:11,260
by looking at the concept of wild cards.

187
00:12:11,260 --> 00:12:15,460
So let's say you had a really messy desktop and you wanted to move all of your images to one folder

188
00:12:15,460 --> 00:12:19,150
and all of your PDFs to another folder and all of your spreadsheets and office files to another folder

189
00:12:19,330 --> 00:12:20,650
using the command line.

190
00:12:20,650 --> 00:12:24,010
How can you use a command that's actually so specific?

191
00:12:24,370 --> 00:12:27,370
Well, you can do that using wild cards.

192
00:12:27,370 --> 00:12:32,530
Wild cards allow you to make your commands really, really specific and also really general, thereby

193
00:12:32,530 --> 00:12:36,730
allowing you to level up in your control over what commands actually operate on.

194
00:12:36,730 --> 00:12:40,030
Now, this is an incredibly useful ability when dealing with files.

195
00:12:40,030 --> 00:12:44,170
So for another dose of epic superpowers, I'll see you in the next video.