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• << : A here document. It is often used to print multi-line strings.

     command << WORD
         Text
     WORD
  

  Here, command will take everything until it finds the next occurrence of WORD, Text in the example above, as input . While WORD is often EoF or variations thereof, it can be any alphanumeric (and not only) string you like. When WORD is quoted, the text in the here document is treated literally and no expansions are performed (on variables for example). If it is unquoted, variables will be expanded. For more details, see the bash manual.

  If you want to pipe the output of command << WORD ... WORD directly into another command or commands, you have to put the pipe on the same line as << WORD, you can't put it after the terminating WORD or on the line following. For example:

     command << WORD | command2 | command3...
         Text
     WORD
  

• <<< : Here strings, similar to here documents, but intended for a single line. These exist only in the Unix port or rc (where it originated), zsh, some implementations of ksh, yash and bash.

    command <<< WORD
  

• << : A here document. It is often used to print multi-line strings.

     command << WORD
         Text
     WORD
  

  Here, command will take everything until it finds the next occurrence of WORD, Text in the example above, as input . While WORD is often EoF or variations thereof, it can be any alphanumeric (and not only) string you like. When any part of WORD is quoted or escaped, the text in the here document is treated literally and no expansions are performed (on variables for example). If it is unquoted, variables will be expanded. For more details, see the bash manual.

  If you want to pipe the output of command << WORD ... WORD directly into another command or commands, you have to put the pipe on the same line as << WORD, you can't put it after the terminating WORD or on the line following. For example:

     command << WORD | command2 | command3...
         Text
     WORD
  

• <<< : Here strings, similar to here documents, but intended for a single line. These exist only in the Unix port or rc (where it originated), zsh, some implementations of ksh, yash and bash.

    command <<< WORD
  

Redirection Operator

• &>, >&, >>& and &>> : (non-standard). Redirect both standard error and standard output, replacing or appending, respectively.

    command &> out.txt
  

The &> variant originates in bash, while the >& variant comes from csh (decades earlier). They both conflict with other POSIX shell operators and should not be used in portable sh scripts. (However >& followed by a file descriptor number is a portable way to redirect a file descriptor, and >&- is a portable way to close a file descriptor.)

POSIX definition

POSIX definition of Redirection Operator

• >& : (per POSIX spec) when surrounded by digits (1>&2) or - on the right side (1>&-) either redirects only one file descriptor or closes it (>&-).

A >& followed by a file descriptor number is a portable way to redirect a file descriptor, and >&- is a portable way to close a file descriptor.

If the right side of this redirection is a file please read the next entry.

• >&, &>, >>& and &>> : (read above also) Redirect both standard error and standard output, replacing or appending, respectively.

    command &> out.txt
  

The &> variant originates in bash, while the >& variant comes from csh (decades earlier). They both conflict with other POSIX shell operators and should not be used in portable sh scripts.

POSIX definition

POSIX definition of Redirection Operator

• >& : (per POSIX spec) when surrounded by digits (1>&2) or - on the right side (1>&-) either redirects only one file descriptor or closes it (>&-).

A >& followed by a file descriptor number is a portable way to redirect a file descriptor, and >&- is a portable way to close a file descriptor.

If the right side of this redirection is a file please read the next entry.

• >&, &>, >>& and &>> : (read above also) Redirect both standard error and standard output, replacing or appending, respectively.

    command &> out.txt
  

The &> variant originates in bash, while the >& variant comes from csh (decades earlier). They both conflict with other POSIX shell operators and should not be used in portable sh scripts.

Redirection Operator

• &>, >&, >>& and &>> : (non-standard). Redirect both standard error and standard output, replacing or appending, respectively.

    command &> out.txt
  

The &> variant originates in bash, while the >& variant comes from csh (decades earlier). They both conflict with other POSIX shell operators and should not be used in portable sh scripts. (However >& followed by a file descriptor number is a portable way to redirect a file descriptor, and >&- is a portable way to close a file descriptor.)