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Pipes and Filters

You can connect two commands together so that the output from one program becomes the input of the next program. Two or more commands connected in this way form a pipe. To make a pipe, put a vertical bar (|) on the command line between two commands.

When a program takes its input from another program, it performs some operation on that input, and writes the result to the standard output. It is referred to as a filter.
The following are some of the filter commands . Click the commands to see the man page and learn different options.

wc- count number of lines words and characters
cut- cut the files vertically character or field wise
paste- vertically paste two files
head- get lines from the beginning of a file
tail-get lines from the end of a file
sort- sort the files contents
grep,egrep,fgrep- search file contents
uniq- unique lines from a sorted file
join- joining two files
tr- translating characters
awk-is a full-featured text processing language 
 
Sample scripts using filters
Display the file name and file size of regular files in the ascending order of file size
 ls -l|tail -n +2|grep -v "^d"|tr -s ' '|cut -d' ' -f5,9|sort -n -k1

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