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Top Forums UNIX for Dummies Questions & Answers When do I use input redirection? Post 302858309 by Don Cragun on Monday 30th of September 2013 04:37:42 AM
Old 09-30-2013
There are also commands that accept one or more pathname operands or read from standard input, but produce different output when no pathname operands are given. For example, if the command:
Code:
wc -l filename

produces the output:
Code:
    4917 filename

the command:
Code:
wc -l < filename

would produce the output:
Code:
    4917

Compare on your own the output produced by:
Code:
wc -l filename1 filename2
    and
cat filename1 filename2 | wc -l

for any two text files you may have lying around.
 

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CAT(1)							      General Commands Manual							    CAT(1)

NAME
cat - catenate and print SYNOPSIS
cat [ -u ] [ -n ] [ -s ] [ -v ] file ... DESCRIPTION
Cat reads each file in sequence and displays it on the standard output. Thus cat file displays the file on the standard output, and cat file1 file2 >file3 concatenates the first two files and places the result on the third. If no input file is given, or if the argument `-' is encountered, cat reads from the standard input file. Output is buffered in the block size recommended by stat(2) unless the standard output is a terminal, when it is line buffered. The -u option makes the output completely unbuffered. The -n option displays the output lines preceded by lines numbers, numbered sequentially from 1. Specifying the -b option with the -n option omits the line numbers from blank lines. The -s option crushes out multiple adjacent empty lines so that the output is displayed single spaced. The -v option displays non-printing characters so that they are visible. Control characters print like ^X for control-x; the delete char- acter (octal 0177) prints as ^?. Non-ascii characters (with the high bit set) are printed as M- (for meta) followed by the character of the low 7 bits. A -e option may be given with the -v option, which displays a `$' character at the end of each line. Specifying the -t option with the -v option displays tab characters as ^I. SEE ALSO
cp(1), ex(1), more(1), pr(1), tail(1) BUGS
Beware of `cat a b >a' and `cat a b >b', which destroy the input files before reading them. 4th Berkeley Distribution May 5, 1986 CAT(1)
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