File viewing: cat, less, more, head, tail

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Transcript

In the previous lecture, we created our first shell script inside that executable permissions. In this next lecture, we will look at applications that allow you to view and edit files. The simplest case for viewing files is to print the content of a file straight into the terminal, which can be done using the cat command. It will print the contents of the file straight in the terminal. It is very useful when you want to print the content of a small file. It's also very useful in the piping operations which we'll cover in the next lectures.

It isn't very suitable for larger files having hundreds of thousands of lines is probably we would just want to see one particular line of the file. For this we can use an another utility called less. And we can see the content of the file printed in the viewer window. We can Press Q to quit. There isn't much we can do in this small file. Let us find a larger file For this, we can go to the directory slash EDC on our file system.

Directory contains configuration files of the operating system. let's print the content of it. As we can see files in the directory are owned by a special user called root. It is the administrator user that has highest privileges. If you want to make changes to system configuration files, you need to be logged in as the root user. But for now, we only want to view these files and we have the read permissions for them.

I would now like to see the files with extension.com I can use wildcards for the last command here. I will choose File sis CTL. Not con which seems large enough for us. If it doesn't exist for you, you can pick any file that is bigger than a few kilobytes. I will now open the file using the last fewer and I will use top auto completion feature to complete the line as we learned in the previous lecture. I can now see the file and it actually doesn't fit into one screen.

Now there are two ways to navigate the file. The straightforward way is to use keyboard navigation keys like up and down Page Up and down. I can go one line forward using the down arrow key. And I can go one line backward using the up arrow key. I can also go one screen forward using page down and one screen backwards using page up. I can go to the end of the file using end and as well as the beginning of it using home.

They're also native shortcuts of the last application. We go one line forward was j, and one line back with K. one page forward with Ctrl F. one page back was Ctrl B, and many more options to navigate. Most common shortcuts are listed in the cheat sheet Don't forget to check it out. Most probably if you open a large file you're only interested in specific lines. airlines or specific configuration output. Last would now help us to find the text we're looking for.

We can search in the file by pressing slash. We will now search for text net. It highlighted all the occurrences of the text on screen now. And we could search for the next occurrence of the word by pressing Enter. And it will bring us to the next occurrence. And I could go back in this search using shift and we can also search backwards from the current location by pressing question mark.

I want to search for the text kernel and it did find it for us. Now I will start searching for Nat. And if I want to cancel the search, I can press Ctrl C. It will bring us back to the main viewer window. After we're finished with looking at the file, we can quit by pressing q We can also go to a specific line in the file bag is a cutie last with additional arguments plus 10. There is an older tentative of the last application called more, you may sometimes tap across it in older systems. It has a less flexible variety of options for navigation, especially for navigation backward, go on page for what was pace, one page back with B.

One line down with enter and cuter quit. We looked at file viewers that allow for navigation. But in some cases we might only be interested in the first or last lines of the file. And we can achieve this using utilities had entail it will print the first 10 lines on to file, we can change the default settings for the number of lines by adding a minus and argument. I will use the history feature of the terminal and edit my previous command it will print the first 20 lines to print the last lines we can use command called tail. And with the same argument minus n, we can change the number of lines that are printed.

The tail command will be very handy when we want to analyze large files such as data reports or compilation logs. For example of the compilation logs errors are usually reported in the last lines of the file. And we can easily see it by printing last 10 or maybe 100 lines so the file also both utilities have entail are very useful when we want to analyze large files using piping. We will cover this in the following lectures. This concludes our lecture about file viewing, and the next lecture will be dedicated to file editing

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