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Shell

In this page will refer as shell to the device that allows to communicate with the system, including terminal, shells and control characters (think about Ctrl-v in the shell).

Normally in the interaction with a client you have to take into account

  • the terminal
  • the shell
  • the application

so, if we want to rename a file named -|^C to foo you have to issue the following keys sequence

m v Space . / - \ | Ctrl-V Ctrl-C Space f o o Return

into the terminal.

Take into account also the path separator and the syntax behind it.

Console&TTY

An useful diagram from here

An important feature of a shell like bash is the stream redirection: by default every process has associated at least three file descriptors

  • stdin (associated with the literal number 0)
  • stdout (associated with 1)
  • stderr (associated with 2)

but it's possible to open/close old/new file descriptors directly from the command line using the following expressions

  • [n]>output: redirect stream n to file output that it's created if needed; the file is truncated
  • [n]>>output: as above but the content is appended
  • [n]>&word: duplicated output file descriptor

Note that the order of redirections is significant. For example, the command

ls > dirlist 2>&1

directs both standard output and standard error to the file dirlist, while the command

ls 2>&1 > dirlist

directs only the standard output to file dirlist, because the standard error was duplicated from the standard output before the standard output was redirected to dirlist. To understand better think of an analogy where > is like the equality operator = and & is instead used as a variable definition like $

https://unix.stackexchange.com/a/37662/32025

1 = /dev/tty
2 = /dev/tty

1> file.txt 2>&1

1 = file.txt
2 = $1           # and currently $1 = file.txt

1 = file.txt
2 = file.txt

2>&1 > file.txt

2 = $1           # and currently $1 = /dev/tty
1 = file.txt

1 = file.txt
2 = /dev/tty

So you need to think about & as a copy of a file descriptor and not as a reference.