Linux Adventures: A Guide to Cat and Redirection

Introduction

The cat command is used in Unix-like operating systems to concatenate and display the contents of files. With "cat," you can effortlessly view the contents of one or more files in one go.

But "cat" isn't just about displaying files—it has a few tricks up its sleeve! You can combine multiple files, creating a mixtape of text, by listing their names after the command.

Furthermore, "cat" can be a fantastic assistant when it comes to redirecting file contents. Using the ">" symbol, you can redirect the output of a command to a new file or overwrite an existing one, just as a cat leaves its paw prints on a fresh canvas. Alternatively, the ">>" symbol appends the output to an existing file. Enough of theory lets dive in to the Lab

The Power of CAT command

cat file1: This command displays the contents of file1 in the terminal.
cat file1 file2: This command displays the contents of both file1 and file2 in the terminal, one after the other.
cat file1 > output.txt: This command redirects the contents of file1 to output.txt, also it overwrites the file if it already exists. If output.txt doesn't exist, it will be created.
cat file1 2> error.txt: This command redirects the error output (stderr) of file1 to error.txt, overwriting the file if it already exists. If error.txt doesn't exist, it will be created.

In the above case there was no file with fileds, hence the error was stored in the error.txt instead of throwing the error message on terminal
cat file1 >> output.txt: This command redirects the contents of file1 to output.txt, appending it to the file if it already exists. If output.txt doesn't exist, it will be created.

In the above case we already had file1 created in out system, hence we appended the output file with the content for file1
cat -T file1: This command displays the contents of file1 and shows tabs as ^I to make them visible.
cat -E file1: This command displays the contents of file1 and adds a $ symbol at the end of each line.
cat -n file1: This command displays the contents of file1 and adds line numbers to each line.
cat -EnT file1: This command displays the contents of file1 and combines the options -E, -n, and -T to show tabs as ^I, add line numbers, and add a $ symbol at the end of each line.

To display the contents of two files at once, you can simply list both file names after the cat command, separated by a space. For example, cat file1 file2 will display the contents of file1 and file2 consecutively in the terminal.

Cat Redirectors

Basically there are two types of redirectors mostly used with the CAT command namely :

> (single greater-than symbol):

>> (double greater-than symbol):

> (single greater-than symbol): The > symbol is used for file redirection and allows you to redirect the output of a command to a file, creating or overwriting the file if it already exists. Here's an example:

[root@192 Desktop]# echo "Hello World!" > greetings.txt

In this example, the text "Hello, World!" is redirected to the file greetings.txt. If the file already exists, it will be overwritten; otherwise, a new file will be created.

>> (double greater-than symbol):

The >> symbol is similar to >, but it appends the output of a command to the end of a file, instead of overwriting it. Consider this example:

[root@192 Desktop]# echo "Namaster Duniya" >> greetings.txt

In this case, the text "Namaster Duniya" is appended to the existing greetings.txt file, preserving the previous content. If the file doesn't exist, it will be created.

File redirection using > and >> is not limited to the echo command; you can redirect the output of other commands or even the contents of multiple files at once. Just remember to use the appropriate symbol and specify the target file name.

So, whether you're saving important notes, capturing program output, or organizing data, file redirection with > and >> provides a convenient way to manage and store information efficiently.

Question #1 Scenario Based Question for the redirectors

Let's consider you want to list down all the items in the /root directory and you have another directory that does not exist and you want to list content of that speicifc directory but still it is an task how to do it lets crack this out

[root@192 Desktop]# ls /root taskdir 1>data.txt

When you execute the above command you will be successfully listing the content of the /root directory in the data.txt file but at the same time it mentioned that the taskdir does not exist. Now you next task is to not to show error on console rather than that print it over the data.txt - Let's cover this

Question #2 Scenario Based Question for the redirectors

Inorder the avoid the same we will make use of 2>> which will make our command more efficient and we will be good to go with it

[root@192 Desktop]# ls /root taskdir 2>>data.txt

The above command does the same as the previous one but the only change here is we have appended the error on the data.txt file and no error was seen upon command execution

I Hope you learned lot about cat and the redirectors see you on the next blog until then Happy Linux-ing!

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