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Full Discussion: Output file redirection
Top Forums UNIX for Dummies Questions & Answers Output file redirection Post 302310458 by aagajaba on Saturday 25th of April 2009 12:16:05 AM
Old 04-25-2009
Output file redirection

Suppose I have a file named a
When I write
cat a>a
The following error message is displayed
cat: a: input file is output file
and my file a is truncated to zero size.
Also the exit status of the last command is 1
Can someone tell me what actually happens when I do so?
 

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CAT(1)								   User Commands							    CAT(1)

NAME
cat - concatenate files and print on the standard output SYNOPSIS
cat [OPTION]... [FILE]... DESCRIPTION
Concatenate FILE(s), or standard input, to standard output. -A, --show-all equivalent to -vET -b, --number-nonblank number nonempty output lines, overrides -n -e equivalent to -vE -E, --show-ends display $ at end of each line -n, --number number all output lines -s, --squeeze-blank suppress repeated empty output lines -t equivalent to -vT -T, --show-tabs display TAB characters as ^I -u (ignored) -v, --show-nonprinting use ^ and M- notation, except for LFD and TAB --help display this help and exit --version output version information and exit With no FILE, or when FILE is -, read standard input. EXAMPLES
cat f - g Output f's contents, then standard input, then g's contents. cat Copy standard input to standard output. GNU coreutils online help: <http://www.gnu.org/software/coreutils/> Report cat translation bugs to <http://translationproject.org/team/> AUTHOR
Written by Torbjorn Granlund and Richard M. Stallman. COPYRIGHT
Copyright (C) 2013 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. SEE ALSO
tac(1) The full documentation for cat is maintained as a Texinfo manual. If the info and cat programs are properly installed at your site, the command info coreutils 'cat invocation' should give you access to the complete manual. GNU coreutils 8.22 June 2014 CAT(1)
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