Linux in a Nutshell, Fifth Edition

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Chapter 6: The Bash Shell and Korn Shell

This is the Title of the Book, eMatter Edition

Copyright © 2006 O’Reilly & Associates, Inc. All rights reserved.

No space should appear between file descriptors and a redirection symbol;

spacing is optional in the other cases.

Bash allows multi-digit file descriptor numbers. The other shells do not.

Examples

$ cat part1 > book

$ cat part2 part3 >> book

$ mail tim < report

$ sed 's/^/XX /g' << END_ARCHIVE

> This is often how a shell archive is "wrapped",

> bundling text for distribution. You would normally

> run sed from a shell program, not from the command line.

> END_ARCHIVE

XX This is often how a shell archive is "wrapped",

XX bundling text for distribution. You would normally

XX run sed from a shell program, not from the command line.

To redirect standard output to standard error:

$ echo "Usage error: see administrator" 1>&2

The following command sends output (files found) to filelist and error messages

(inaccessible files) to file no_access:

$ find / -print > filelist 2>no_access

Coprocesses

Coprocesses are a feature of the Korn shell only.

Moving the coprocess input and output file descriptors to standard file descrip-

tors allows you to open multiple coprocesses.

cmd >& file Same. Bash only.

cmd > f1 2>f2 Send standard output to file f1, standard error to file f2.

cmd | tee files Send output of cmd to standard output (usually the terminal) and to files