Sams Teach Yourself Shell Programming in 24 Hours, Second Edition

Input/Output

This section discusses I/O. Table A.1 describes the standard UNIX file descriptors, whereas other sections describe input and output redirections and “here” documents.

Table A.1. Summary of Standard UNIX I/O

Abbreviation	I/O description	File Descriptor
STDIN	Standard input	0
STDOUT	Standard output	1
STDERR	Standard error	2

Input and Output Redirection

Input and output redirection can be performed as follows:

cmd > file	save STDOUT from UNIX command in file
cmd 1> file	same as above
cmd >> file	append STDOUT from UNIX command to file
cmd 1>> file	same as above
cmd 2> file	save STDERR from UNIX command in file
cmd 2>> file	append STDERR from UNIX command in filecmd < file provide STDIN to UNIX command from file instead of keyboard ...