Advanced Bash−Scripting Guide

# Thanks to Stephane Chazelas for providing this instructive example.
exit 0
[52] The return command is a Bash builtin.
Advanced Bash−Scripting Guide
[53] Herbert Mayer defines recursion as "...expressing an algorithm by using a simpler version of that same
algorithm..." A recursive function is one that calls itself.
[54] Too many levels of recursion may crash a script with a segfault.
#!/bin/bash
recursive_function ()
{
(( $1 < $2 )) && f $(( $1 + 1 )) $2;
# As long as 1st parameter is less than 2nd,
#+ increment 1st and recurse.
}
recursive_function 1 50000 # Recurse 50,000 levels!
# Segfaults, of course.
# Recursion this deep might cause even a C program to segfault,
#+ by using up all the memory allotted to the stack.
# Thanks, S.C.
exit 0 # This script will not exit normally.
[55] However, aliases do seem to expand positional parameters.
[56] This does not apply to csh, tcsh, and other shells not related to or descended from the classic Bourne
shell (sh).
[57] The entries in /dev provide mount points for physical and virtual devices. These entries use very little
drive space.
Some devices, such as /dev/null, /dev/zero, and /dev/urandom are virtual. They are not
actual physical devices and exist only in software.
[58] A block device reads and/or writes data in chunks, or blocks, in contrast to a character device, which
acesses data in character units. Examples of block devices are a hard drive and CD ROM drive. An
example of a character device is a keyboard.
[59] Certain system commands, such as procinfo, free, vmstat, lsdev, and uptime do this as well.
[60] Rocky Bernstein's Bash debugger partially makes up for this lack.
[61] By convention, signal 0 is assigned to exit.
[62] Setting the suid permission on the script itself has no effect.
[63] In this context, " magic numbers" have an entirely different meaning than the magic numbers used to
designate file types.
[64] ANSI is, of course, the acronym for the American National Standards Institute.
[65] See Marius van Oers' article, Unix Shell Scripting Malware, and also the Denning reference in the
bibliography.
[66] Chet Ramey promises associative arrays (a Perl feature) in a future Bash release.
[67] This is the notorious "flog it to death" technique.
[68] Those who can, do. Those who can't... get an MCSE.
[69] If no address range is specified, the default is all lines.
Appendix J. Copyright 445