in_out_std_streams.md

Standard Streams

All processes have (from os) std steams, to which they can read/write.

• cin

• cout
• cerr

Default

• keyboard - cin ,
• screen - cout, cerr

But can be changed by

• Redirect to/from file
  • cin (<) c < file_in cin of process c is file called file_in

  • cout(> or 1>), cerr (2>)

    • c1 > file_out
    • c1 1> file_out cout of c1 is file called file_out

    • c1 2> file_err
      cerr of c1 is file called file_err

    • c1 2> file_err > file_out
      cerr of c1 is file called file_err, and its cout is file called file_out

    • c1 > file_both 2>&1
    • c1 > file_both &> cerr and cout ...... file_both (note: order of matters: c1 2>&1 > file_both is not the same - cerr goes to the original dest of cout)

• Pipe ( | ) between processes

  • c1 | c2 cout of c1 is cin for c2

    • Note: c2 does not wait for c1 to finish before starting - both c1 and c2 are started (almost) simultaneously.
  
  
  • c1 | tee [-a] file_out tee writes it cin to both its cout and file_out (appending if -a is specified)