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Unix in a Nutshell, 4th Edition
book

Unix in a Nutshell, 4th Edition

by Arnold Robbins
October 2005
Intermediate to advanced content levelIntermediate to advanced
908 pages
46h 42m
English
O'Reilly Media, Inc.
Content preview from Unix in a Nutshell, 4th Edition

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 noclobber option is set.

Redirection using file descriptors

cmd ...

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Publisher Resources

ISBN: 0596100299Errata Page