Linux in a Nutshell, 6th Edition

Output Redirections

For print and printf, dest-expr is an optional expression that directs the output to a file or pipe.

> file

Direct the output to a file, overwriting its previous contents.

>> file

Append the output to a file, preserving its previous contents. In both this case and the > file case, the file will be created if it does not already exist.

| command

Direct the output as the input to a system command.

|& command

Direct the output as the input to a coprocess. gawk only.

Be careful not to mix > and >> for the same file. Once a file has been opened with >, subsequent output statements continue to append to the file until it is closed.

Remember to call close( ) when you have finished with a file, pipe, or coprocess. If you don’t, eventually you will hit the system limit on the number of simultaneously open files.