Linux Redirects

There are 3 redirects:
Basically, when we run a command in terminal, belwo three files are created.

Company	File Descriptor
Standard Input (stdin)	0
Standard Output (stdout)	1
Standard Error (stderr)	2

Output (stdout-1)

• Output of a command is shown in terminal.
• To route output in file using >. This clears all the previous content and then overwrites with the new content.
  • hostname > file_name
• To append output in existing file using >>. This appends the new content to the previous existing content.
  • pwd » file_name

Error (stderr - 2)

• If any command gives your error then it is considered as stderr-2
• We can redirect the error to a file:
  • Eg: cd /root/ 2>error_file
  • This prevents the error from showing up in the terminal but writes all the error in a file.

• To redirect both standard output and error to a file: Eg:-

    Input: hostname >> std_err_out 2>&1
    Input: cat std_err_out
    Output: <Host Name of the Computer>
  
    Input: cd /root/  >> std_err_out 2>&1
    Input cat std_err_out
    Output: 
        <Host Name Of The Computer>
        <Error>
  

Input (stdin - 0)

• Input is used when feeding file contents to a file

• Eg:-

    cat < file_name
    cat << EOF