I/O Redirection

Table B-9 shows a complete list of I/O redirectors. (This table is also included earlier as Table 7-1.) Note that there are two formats for specifying standard output and error redirection: &>file and >&file. The second of these, and the one used throughout this book, is the preferred way.

Table B-9. I/O redirectors

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Redirector

Function

cmd1 | cmd2

Pipe; take standard output of cmd1 as standard input to cmd2

> file

Direct standard output to file

< file

Take standard input from file

>> file

Direct standard output to file; append to file if it already exists

>| file

Force standard output to file even if noclobber is set

n>| file

Force output to file from file descriptor n even if noclobber set

<> file

Use file as both standard input and standard output

n<> file

Use file as both input and output for file descriptor n

<< label

Here-document

n > file

Direct file descriptor n to file

n < file

Take file descriptor n from file

>> file

Direct file descriptor n to file; append to file if it already exists

n>&

Duplicate standard output to file descriptor n

n<&

Duplicate standard input from file descriptor n

n>&m

File descriptor n is made to be a copy of the output file descriptor

n<&m

File descriptor n is made to be a copy of the input file descriptor

&> file

Directs standard output and standard error to file

<&-

Close the standard input

>&-

Close the standard output

n>&-

Close the output from file descriptor n

n<&-

Close the input from file descriptor n

n>&word

If n is not specified, the standard output (file descriptor 1) is used; if the digits in word do not specify a file descriptor open for output, a redirection error occurs; as a special case, if n is omitted, and word does not expand to one or more digits, the standard output and standard error are redirected as described previously

n<&word

If word expands to one or more digits, the file descriptor denoted by n is made to be a copy of that file descriptor; if the digits in word do not specify a file descriptor open for input, a redirection error occurs; if word evaluates to -, file descriptor n is closed; if n is not specified, the standard input (file descriptor 0) is used

n>&digit-

Moves the file descriptor digit to file descriptor n, or the standard output (file descriptor 1) if n is not specified

n<&digit-

Moves the file descriptor digit to file descriptor n, or the standard input (file descriptor 0) if n is not specified; digit is closed after being duplicated to n