A pipe is an interprocess connection between file descriptors of two processes. A pipe is created with the POSIX pipe() function (from
Every program that runs on the command line has three data streams connected to it: STDIN(0) - standard input, STDOUT (1) - standard output - data printed by the program, STDERR(2) - standard error.
There are ways to connect streams between programs and files called piping and redirections.
Piping is a mechanism for sending data from one program to another using the "|" operator. The operator feeds the output from the program on the left as input to the program on the right.
Example
$ cat two_columns
column1:cloth
column2:strawberries
column3:fish
column4:chocolate
column5:punch cards
$ cat two_columns | awk -F: '{print $1}'
column1
column2
column3
column4
column5
$ cat two_columns | awk -F: '{print "HAS: " $2}'
HAS: cloth
HAS: strawberries
HAS: fish
HAS: chocolate
HAS: punch cards
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