Команды с использованием конвейера

Piping hot commands

Pipes let programs work together by connecting the output from one to be the input for another. Pipes are built using a vertical bar (|) as the pipe symbol.

Say you help your eccentric Aunt Hortense manage her private book collection. You have a file named books containing a list of her holdings, one per line, in the format 'author:title', something like this:

$ cat books

Carroll, Lewis:Through the Looking-Glass

Shakespeare, William:Hamlet

Bartlett, John:Familiar Quotations

Mill, John Stuart:On Nature

London, Jack:John Barleycorn

Bunyan, John:Pilgrim's Progress, The

Defoe, Daniel:Robinson Crusoe

Mill, John Stuart:System of Logic, A

Milton, John:Paradise Lost

Johnson, Samuel:Lives of the Poets

Shakespeare, William:Julius Caesar

Mill, John Stuart:On Liberty

Bunyan, John:Saved by Grace

This is somewhat untidy, as they are in no particular order. But we can use the sort command to straighten that out:

$ sort books

Bartlett, John:Familiar Quotations

Bunyan, John:Pilgrim's Progress, The

Bunyan, John:Saved by Grace

Carroll, Lewis:Through the Looking-Glass

Defoe, Daniel:Robinson Crusoe

Johnson, Samuel:Lives of the Poets

London, Jack:John Barleycorn

Mill, John Stuart:On Liberty

Mill, John Stuart:On Nature

Mill, John Stuart:System of Logic, A

Milton, John:Paradise Lost

Shakespeare, William:Hamlet

Shakespeare, William:Julius Caesar

Ah, now you have a list nicely sorted by author. How about getting a list just of authors, without titles? You can do that with the cut command:

$ cut -d: -f1 books

Carroll, Lewis

Shakespeare, William

Bartlett, John

Mill, John Stuart

London, Jack

Bunyan, John

Defoe, Daniel

Mill, John Stuart

Milton, John

Johnson, Samuel

Shakespeare, William

Mill, John Stuart

Bunyan, John

A little explanation here. The -d option chose a colon as the delimiter (separator). This tells cut to break up each line wherever a delimiter appears, and each separate part of the line is called a field. In our format, the author's name appears as the first field, so we have put a 1 with the -f option to tell cut that we want to see just that field.