execline
Software
skarnet.org

The | program

| runs two commands with a pipe between them.

Interface

In an execlineb script:

     | [ -d ] [ -r | -w ] { prog1... } prog2...

• | reads prog1... in a block and unquotes it.
• It runs prog1... as a child process and execs into prog2..., with a pipe between prog1's stdout and prog2's stdin.
• prog1's pid is available in prog2 as the ! environment variable.

Options

• -d : run prog1... as a grandchild of |. This is meant to prevent a zombie from hanging around if prog2... fails to wait for its children.
• -r : make prog1... the writer and prog2... the reader. This is the default.
• -w : make prog1... the reader and prog2... the writer.

Notes

• You can easily create a chain of pipes: | a "" | b "" c is roughly equivalent to sh -c 'exec a | b | c', except that shells usually run c as a child process like a and b, and exec has no effect.