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.

Command Forms

Examples

$ nroff file > file.txt & Format in the background

$ cd; ls Execute sequentially

$ (date; who; pwd) > logfile All output is redirected

$ sort file | pr -3 | lp Sort file, page output, then print

$ vi `grep -l ifdef *.c` Edit files found by grep

$ egrep '(yes|no)' `cat list` Specify a list of files to search

$ egrep '(yes|no)' $(cat list) POSIX version of previous

$ egrep '(yes|no)' $(< list) Faster, not in POSIX

$ grep XX file && lp file Print file if it contains the pattern;

$ grep XX file || echo "XX not found" Otherwise, echo an error message

Redirection Forms

The usual input source or output destination can be changed, as seen in the

following sections.

Simple redirection

cmd > file

Send output of cmd to file (overwrite).

cmd >> file

Send output of cmd to file (append).

Syntax Effect

cmd & Execute cmd in background.

cmd1 ; cmd2 Command sequence; execute multiple cmds on the same line.

{ cmd1 ; cmd2 ; } Execute commands as a group in the current shell.

(cmd1 ; cmd2) Execute commands as a group in a subshell.

cmd1 | cmd2 Pipe; use output from cmd1 as input to cmd2.

cmd1 'cmd2' Command substitution; use cmd2 output as arguments to cmd1.

cmd1 $(cmd2) POSIX shell command substitution; nesting is allowed.

cmd $((expression)) POSIX ...