In my last post I talked briefly about a very important concept when it comes to the command line,Standard Input and Standard Output. If you would like to have a read you can catch up here :
This post is an introduction on the different ways redirecting input and output can be achieved, what appending is and how it works and in the meantime we will explore ways to check our work during the process and make sure we're on the right path.
Through redirection we direct the input and output of a command to and from different files. It essentially reroutes standard input, standard output and standard error to and from different locations.
To achieve redirection we use
> which is called the
redirect operator.Let's take an example:
echo "hello, world" > world.txt
hello, world is entered as the standard input. The
redirect operator takes the string output from echo which is the
hello, world printed on the screen, and redirects it to a file called
world.txt. This way a new file is created containing already text.
To add more lines of text to a file that already exists we use
>> , the
echo "I am learning the command line" >> world.txt
The appending operator is a useful addition(see what I did there?) to the normal redirect operator.It adds the line to the end of the existing file. It can be used when we want to build up a file gradually, adding new parts to the file as we go along.
To view the contents of files on the screen we use the command
cat. That use of the command is common, however as the name is short for
concatenate , we can also use it to combine the contents of multiple files and therefore it takes multiple arguments. In that case the order matters and we can reverse the order of the files, depending on what content we want to go first.
In the above example the contents of the file world.txt are displayed.
cat world.txt > coding.txt
In this case,
cat takes the contents of the file on the left and redirects it to the file on the right.The redirect operator overwrites any original content that may exist in
coding.txt. If the file
coding.txt doesn't exist already, it will be created in the process.The new file will be located in the current working directory and it's contents will be the exact same as those of
cat world.txt hello.txt > coding.txt
In this case the output of
world.txt goes first in the file
coding.txt followed by the output of
cp world.txt coding.txt
can work similar to
cat world.txt > coding.txt
Both commands overwrite the content of
coding.txt with that of
world.txt.The difference between them is
cp works like
copy and paste,it copies files and directories.
cat is more like
cut and paste,it is transferring files and directories and creating new files in the process of doing that.
Whenever redirecting or appending contents of files, it's always a good idea to use the
cat command to make sure that our files have the right content and we haven't made any mistakes.
Thank you for reading! 😃