Redirection Forms
|
File descriptor |
Name |
Common abbreviation |
Typical default |
|
0 |
Standard input |
stdin |
Keyboard |
|
1 |
Standard output |
stdout |
Screen |
|
2 |
Standard error |
stderr |
Screen |
The usual input source or output destination can be changed, as seen in the following sections.
Simple redirection
-
cmd>file Send output of cmd to file (overwrite).
-
cmd>>file Send output of cmd to file (append).
-
cmd<file Take input for cmd from file.
-
cmd<<text The contents of the shell script up to a line identical to text become the standard input for cmd (text can be stored in a shell variable). This command form is sometimes called a Here document. Input is usually typed at the keyboard or in the shell program. Commands that typically use this syntax include cat, ex, and sed. (If
<<-is used, leading tabs are stripped from the contents of the here document , and the tabs are ignored when comparing input with the end-of-input text marker.) If any part of text is quoted, the input is passed through verbatim. Otherwise, the contents are processed for variable, command, and arithmetic substitutions.-
cmd<<<word Supply text of word, with trailing newline, as input to cmd. (This is known as a here string , from the free version of the rc shell.) Not ksh88.
-
cmd<>file Open file for reading and writing on the standard input. The contents are not destroyed.[*]
-
cmd>|file Send output of cmd to file (overwrite), even if the shell’s
noclobberoption is set.
Redirection using file descriptors
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|