Difference between Pipe & Redirection
Pipe is used to pass output to another Program or Utility.
- thing1 | thing2
- thing1’s output s will be passed to things2 Program or Utility.
Redirect is used to pass output to either a File or Stream.
- thing1 > thing2
- thing1’s outputs will be placed in a file called thing2.
With Pipe, the standard output of one command is fed into the standard input of another.
$ ls | grep "java"
It will find all the file names from ls that contain “java” string.
Standard output directs its contents to the display. To redirect standard output to a file, the “>” character is used.
$ ls > file_list.txt
In this example, all the file names from ls command will be written in an file named file_list.txt. Since the output of ls was redirected to the file, no results on the display. Each time the command above is repeated, file_list.txt is overwritten (from the beginning) with the output of the command ls. If you want the new results to be appended to the file instead, use “>>“.
$ ls >> file_list.txt
Standard Input gets its contents from the keyboard, but like standard output, it can be redirected. To redirect standard input from a file instead of the keyboard, the “<” character is used.
$ sort < file_list.txt
Sort command print the contents of file_list.txt. We could redirect standard output to another file.
$ sort < file_list.txt > sorted_file_list.txt
As you can see, a command can have both its input and output redirected. The redirection operators (the “<” and “>”) must appear after the other options and arguments in the command.
- sort: Sorts standard input then outputs the sorted result on standard output.
- uniq: Given a sorted stream of data from standard input, it removes duplicate lines of data (i.e., it makes sure that every line is unique).
- grep: Examines each line of data it receives from standard input and outputs every line that contains a specified pattern of characters.
- fmt: Reads text from standard input, then outputs formatted text on standard output.
- pr: Takes text input from standard input and splits the data into pages with page breaks, headers and footers in preparation for printing.
- head: Outputs the first few lines of its input. Useful for getting the header of a file.
- tail: Outputs the last few lines of its input. Useful for things like getting the most recent entries from a log file.
- tr: Translates characters. Can be used to perform tasks such as upper/lowercase conversions or changing line termination characters from one type to another (for example, converting DOS text files into Unix style text files).
- sed: Stream editor. Can perform more sophisticated text translations than tr.
- awk: An entire programming language designed for constructing filters. Extremely powerful.