Linux - Input, Output and Pipeline

I/O Streams: An input stream handles data flowing into and out of a program - stdin - stdout - stderr

We echo the text woof here, ​but instead of sending it to our screen by default, ​we’re going to redirect the output to a file ​using the standard out redirector operator. ​Let’s verify, and there it is. ​This overrides any file named ​dog.txt with the content woof.

 ​If we don’t want to overwrite an existing file, ​we can use the append operator ​or >>. ​Echo woof dog.txt.

standard in redirector operator denoted by <  ​Instead of getting input from the keyboard, ​we can get input from files. ​This command is exactly the same as cat file_input. ​The difference here is that we aren’t ​using our keyboard input anymore. ​We’re using the file as standard in.

 ​Standard error displays ​error messages which you can get by ​using the 2> redirector operator. ​Just like Windows, the 2 ​is used to denote standard error. ​To redirect just the error messages of some output, ​you can use something like this, ​ls /dir/fake_dir 2> error_output.tx  

Remember the dollar sign null variable ​that we used in Windows to ​toss unwanted output into a metaphorical black hole? ​We have something like that in Linux too, ​there’s a special file on Linux ​called the /dev/null file. Let’s say we want to filter out the error messages in ​a file and just want to see standard out messages. ​We could do something like this. Now our output is filtered from error messages

Remember how we talked about ​taking the output of one command and ​using it as the input of ​another command with the Windows pipeline? ​Well the same thing exists in Linux. ​The pipe command ( | ) allows us to do this. ​Let’s say we want to see which sub-directories in ​the /etc directory contain the word Bluetooth. Now without even looking through the directory, ​we’re able to quickly see if ​the Bluetooth directory is in here. There it is.