[Day 2] 7. Redirection

Console Standard Files

The console operates with three internal standard files:

1. Standard Input File: Used to take input.
2. Standard Output File: Used to display output.
3. Standard Error File: Used to display error messages.

These files are collectively referred to as standard files.

There are two ways to give output of one command to another: Redirection and Pipes

Redirection

Redirection allows you to control the flow of input and output in the console. There are three main types of redirection:

1. Input Redirection:

   • Instead of taking input from the standard input file, you can take input from another file.
   • Operator:
     Copy

     <

   • Example:
     Copy

     cat < test.txt

2. Output Redirection:

   • Instead of writing output to the standard output file, you can write it to another file.
   • Operator:
     Copy

     >

   • Example:
     Copy

     ls > lsout.txt

3. Error Redirection:

   • Instead of writing errors to the standard error file, you can write errors to another file.
   • Operator:
     Copy

     2>

   • Example:
     Copy

     command 2> error.txt

   • You can redirect both standard output and standard error to the same file using:
     Copy

     command > output.txt 2>&1

Pipes

Pipes allow you to connect the output of one command to the input of another. There are two types of pipes:

1. Named Pipe:

   • Created using the
     Copy

     mkfifo()

     function.
   • Can be used for two logically unrelated processes.

2. Unnamed Pipe:

   • Created using the
     Copy

     pipe()

     function.
   • Can be used for two related processes.

Note: Both pipes function similarly, but they are used under different circumstances.

!7. Pipe.png

Additional Notes

• The
  Copy

  bc

  command can be used to perform mathematical operations, and input redirection can also be applied here.
• You can combine input and output redirection together, but not all commands support this.