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[No audio]

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Hello everyone and welcome again to

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our newer lesson sed command.

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sed command is a substitute command which

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replaces or substitute a text with another

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text or manipulate your file.

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It is a very very powerful command.

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So what are the few things that sed command does?

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It replaces a string in a file with another string.

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So a string is a word, a sentence, text

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message or any kind of text message inside of

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your file that you want to replace.

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It finds and deletes a line.

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So if a line has ABC and you want to get rid

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of that line in that text file, well you could go in

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and use the sed command and delete that line that contains ABC.

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Now wait a second Imran hey, why can't I do the same thing

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when I go to vi and find the line and delete it?

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Yes, you could definitely do that.

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But what if you have a file that has let's

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say a million lines, and in those million lines you

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probably have at least 1000 lines that has ABC.

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Now are you going to go into the file

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and delete or replace that string one by one?

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You think that is efficient? Not at all.

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So that's why sed command is so powerful.

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That allows us to manipulate the text inside a file.

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Another example that we'll learn is how

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to remove empty lines from our file.

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If there are more than one empty lines,

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how can you get rid of it?

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Yes, of course, going back to the same thing that you

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could go into the vi and dd and remove it.

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But again, this is not productive.

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Remove the first line or number of lines

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in a file, to replace tabs with spaces.

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These are the very few examples of sed commands that

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I'm going to go over and substitute within vi editor.

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So if you are already in vi, and you

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wanted to replace a text xyz or text or

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anything with another text or another word, you could

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also do by going straight into the vi.

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But again, am I negating my

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statement, what I said before?

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No, because when you are going to the vi

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and you look for one word and then you

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replace it, again it's a manual process.

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But there is another way in vi that

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you could just find that text one time

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and it replaces it everywhere in one shot.

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And if there is so much more and more, that sed command

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has to offer. So I'm going to log into my Linux machine,

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I'm going to log in as a PuTTY client and I will

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show you a few examples of how sed command works.

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I'm logged in as myself.

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I am in my home directory.

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I have a file in my home directory,

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that is called, let's do ls -ltr here,

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that is called seinfeld-characters.

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So if you do cat on seinfeld-characters,

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you'll see all these characters of Seinfeld.

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Again, it's just a list of all

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the characters that played in Seinfeld.

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If you do not have that file or if you

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did not create that file previously, then go ahead and

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you could just pause it right here and create that

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file with all those names that I have.

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Or if you want to use a

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different file, different names, that's fine.

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It's just the example that I'm going to

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be using to explain how sed command works.

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So I already have this file.

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Now, the first thing I wanted to do,

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let's say, what if I wanted to replace

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one of the word with a different word?

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Let's say I wanted to replace Kenny.

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There's a character named Kenny Bania.

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How about if I wanted to replace

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his name from Kenny to Lenny?

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You would use the command sed, single quote s for substitute,

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Kenny with Lenny, so slash Lenny,

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and slash again,

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and if there are more than one

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Kenny, then you could type g,

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because this g stands for global.

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It will replace the entire file

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wherever you have the word Kenny.

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So by default, I always use g.

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You should also get into the habit of

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g if you want to replace it everywhere.

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So you close the single quote, and then

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you type the name of the file where

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you are trying to replace the word Kenny.

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Hit enter.

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And now you will see, at the

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bottom, it is replaced with Lenny.

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Now, another thing I do want to mention that this

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is going to display the change only on the screen.

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It is not actually going to make a change in the file.

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So if you cat out the file, you

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will see the name Kenny still there.

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But didn't we just replace it with Lenny?

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Yes, we did, but it did not

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make the change inside the file.

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It only makes the change to the screen.

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And if you want to have that output to

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another file, you could do that and that change

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will be reflected in the newer file.

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But if you want to make a change to the existing

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file, then what you have to do is, you come back

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to the same command by hitting up arrow key and you

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type -i, that is to insert the changes into the

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file, the same command, and you hit enter.

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Now, when you do cat seinfeld-characters, you'll

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see the name has changed to Lenny permanently.

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So this is how you replace Kenny

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with Lenny and save the file.

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Now, let's see,

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what if you want to replace the word Costanza.

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[No audio]

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So it works the same way.

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So you do sed

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[No audio]

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substitute Costanza,

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[No audio]

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and this time you just don't want to replace anything.

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You just want to remove that word.

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So you just put Costanza and

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don't put anything in there,

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g, and the name of the file characters.

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You see anyone who had the

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last name Costanza, that is gone. See right here.

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Frank Costanza is gone.

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Stell Castanza is gone.

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Another Costanza I have, the bottom is gone.

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George Costanza is gone.

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But again, this is gone only on the screen.

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And if you want to make a changes to the

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file, you have to use the -i option.

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I don't want to use the -i option this time

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because I wanted to show you how the sed works.

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So this way the file won't change.

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Let's just confirm our file has all the correct

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names that I want to have them in it.

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So it does have it.

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Next one I wanted to show you is how

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to find a string of line and remove it.

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If you see, this is the second

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one in our slide, find and delete.

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So what if I wanted to delete

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every line that has the word Seinfeld?

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So the command to do that is sed

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[No author]

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Seinfeld,

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and this time type d.

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[No audio]

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d is to delete any character

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or any word that comes up, that matches Seinfeld,

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that line will be deleted.

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So I am not using -i option because it will

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actually make the changes to my file and save it.

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I just want to show you.

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So I'll just run it and you will see

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all the lines that had the Seinfeld are gone.

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See, none of this has the word Seinfeld in it.

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So that's how you replace or delete a

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line that matches a keyword or a word.

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The next thing I wanted to show you is

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how you could remove empty lines from a file.

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So if I have empty lines, let's make the empty line.

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I'll go into seinfeld-characters and

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I'm going to make empty lines.

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[No audio]

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So I have four empty lines, right?

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I'll just make one empty line right here as well, five empty lines.

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Now I'm going to save that file,

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cat seinfeld-characters,

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[No audio]]

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and you will see right here I have, five empty lines.

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[No audio]

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five empty lines.

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I wanted to get rid of these five empty lines.

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The command to do that is sed,

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[No audio]

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slash,

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[No audio]

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cap, cap shows

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that anything that starts, which is right above number

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six and dollar, anything that ends with dollar meaning

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nothing, then just delete that, sorry, seinfeld-characters.

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So anything that is starting or anything that

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is ending has nothing in the middle, which

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is the empty file of course, right.

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So whatever that finds, please go ahead and delete it.

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So hit enter and you'll see everything is gone.

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But now if you do seinfeld-character again,

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you'll see it will still have the line. Why?

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Because we did not specify the -i option and I

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want you to go ahead and specify -i option.

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Do a seinfeld-character, and you'll see

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all the empty lines are gone.

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Now what if I wanted to remove

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the first line in a file?

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I just want to remove Jerry Seinfeld, which

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is the first line of the file.

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So I will do sed, quote, 1d, quote close, the name of

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the file, and you'll see the first line was Jerry Seinfeld.

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That is gone. Now

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of course, again, I keep saying it is not going to

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affect our file because we did not use -i option.

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Now, what if you want to remove first two lines?

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Well, hit up arrow key and just type one comma

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two and it will delete the first two lines.

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That's how you delete two, three, or four, or more lines.

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Now, what if you have tabs in your file

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and you want to remove those tabs with spaces?

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So if I do vi on seinfeld-characters and instead of

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spaces, I'll just put tabs, tabs, and tabs, save the file.

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You could do cat seinfeld-character.

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You see three lines have tab.

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I wanted to remove all the

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tabs inside the file with space.

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So the command to do that is sed substitute slash,

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we have to use backslash and t.

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That tells the operating system or the

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shell that this is a tab.

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Anywhere you find tab, please remove it

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with space and apply it globally.

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seinfeld-characters, you see,

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oh, didn't like something,

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[No audio]

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one second.

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[No audio]

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Oh, my mistake.

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I used backslash here.

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So I have to use forward slashes here, because this slash

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right here and this slash right here in the middle right

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here is the string that we are trying to replace.

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We are trying to replace that string with what,

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with empty line.

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So now that should work.

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And there it is.

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It did work, but it is again

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not going to impact our file.

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I'm going to use that command with -i

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option so it will make the change to my

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file and bring it back to this original content.

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[No audio]

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Okay, so now that's how you

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actually replace tabs with spaces.

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If you want to do the same thing, replace spaces with tabs,

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you could do the same thing, but just

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switch up backslash t with the second space holder.

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So you move this thing to here.

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So it will remove everywhere, let's say,

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even if you want to try it,

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t, and here I have,

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so any spaces that's in

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there, please replace it with tab.

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And I have to put this here.

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[No audio]

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Okay. So I believe

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[No audio]

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seinfeld-characters, and there you have all the tabs in there.

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I did not want to make the changes.

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That's why when I was checking it,

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it was not coming up. Anyway,

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I wanted to bring it back.

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To bring it back, I'll run the earlier command, which

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is this replace tab with spaces and hit enter.

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And now do seinfeld-characters, and you'll see

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my format is back the way I want.

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Okay, now, what if I wanted to show only

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lines from 12 to 18 from a file.

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So I just wanted to view 12 to 18.

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So 1, 2,3, 4, 5, 6, 7, 8, 9, 10, 11, 12.

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So I wanted to see all the lines starting with J Perterman

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all the way to the end, which is the 18th line.

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I don't want it to view any of these lines.

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So for that, you'll use the command sed again,

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with -n option, 12 from 12 to 18,

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p is the option that you have to pick

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and you hit enter and you will see right

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here it's giving me from line 12 to 18.

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Now what if you want to view the opposite way, meaning

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you want to view everything except line 12 to 18.

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Then you will run the command sed,

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now don't use -n, use 12,18d this time

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and seinfeld-characters, and you'll see you have all the

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results from the top except starting line 12 to 18.

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Now what if you wanted to put a space in

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your file like every name, there should be a space,

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there should be an empty line after each character.

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So you'll do sed, just G, seinfeld-characters and

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you'll see every line has a space, empty line,

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then the name, empty line, then the name.

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This is how you could add it.

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But of course it's not going to impact our file.

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You could have that changes by putting in -i option.

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Okay, now what if you wanted to replace like, let's

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say if I have seinfeld-character and I want to

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replace Seinfeld with s or any other name, but I

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do not want to replace number line 8.

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So 1, 2, 3, 4, 5, 6, 7, 8, I want to replace

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Seinfeld with S, except the 8th Seinfeld.

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So you do sed single quote, do not

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do 8, and substitute Seinfeld with s.

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Do it globally,

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[No audio]

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seinfeld-characters.

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Okay, see it did change, oh 1 second.

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Let me see.

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[No audio]

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Now umm,

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[No audio]

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let's see.

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[No audio]

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So if I just type 8 just up to seinfeld for s,

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so it is still not doing it.

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Am I doing something wrong?

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Yes, I am doing something wrong.

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See, sometimes just tiny bit of

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a mistake makes a huge difference.

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If you notice there is no such word as seinfled.

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I put seinfled.

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Alright, it's a good exercise.

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You hit enter, you see every Seinfeld text

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or word has been changed with S.

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But now let's go back to our original question.

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I don't want to replace number eight.

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I'll fix my spelling, hit enter and you will see

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all of them have changed except line number eight.

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Now the last one I talked about

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substitute while you are in vi editor.

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So go ahead and type vi, the name of

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the file, and now you are in vi editor.

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Now what if you want to replace

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every seinfeld-characters while you are in vi.

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So you will do colon

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percent sign, s for substitute, slash,

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Seinfeld to

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[No audio]

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Peter.

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Right. You might replace everyone

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of them and hit enter, and you'll see every

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Seinfeld has been replaced with the word Peter.

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That's how you make the change

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while you are in vi editor.

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Now I want you to go ahead and try it out.

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I have also an article mentioned here in this

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lesson that you could view that article and try

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all the different commands. Again, sed command is very

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powerful if you really know inside out.

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So I would encourage you to try many different ways.

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Go ahead and do your Google, go online and search

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for anything that you wanted to do with sed.

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And I promise you, every time you will type something,

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make sure you type, like how to

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replace a string in sed command.

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Make sure you put in sed command.

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And I'm telling you, you're going to

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find tons of article out there

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people, again, have done an amazing job who

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have helped people, and you could look at

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their article and see how things are done.

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You can learn on that.

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All right, if you have any questions about sed command, you

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could just simply send me an email or message me.

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Alright, good luck.

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[No audio]