10-12-2008
The code is making sure that if the pid variable is unset it becomes null (or zero-length).
unset and null are different. null means that variable exists in memory and is "", unset means bash never heard of it before.
In coding, whenver you create a new variable you want to set it to a known state. In C you set a string to be zero-length, an integer to zero. This is the same idea.
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LEARN ABOUT CENTOS
bashbug
BASHBUG(1) General Commands Manual BASHBUG(1)
NAME
bashbug - report a bug in bash
SYNOPSIS
bashbug [--version] [--help] [email-address]
DESCRIPTION
bashbug is a shell script to help the user compose and mail bug reports concerning bash in a standard format. bashbug invokes the editor
specified by the environment variable EDITOR on a temporary copy of the bug report format outline. The user must fill in the appropriate
fields and exit the editor. bashbug then mails the completed report to bug-bash@gnu.org, or email-address. If the report cannot be
mailed, it is saved in the file dead.bashbug in the invoking user's home directory.
The bug report format outline consists of several sections. The first section provides information about the machine, operating system,
the bash version, and the compilation environment. The second section should be filled in with a description of the bug. The third sec-
tion should be a description of how to reproduce the bug. The optional fourth section is for a proposed fix. Fixes are encouraged.
ENVIRONMENT
bashbug will utilize the following environment variables if they exist:
EDITOR Specifies the preferred editor. If EDITOR is not set, bashbug defaults to emacs.
HOME Directory in which the failed bug report is saved if the mail fails.
TMPDIR Directory in which to create temporary files and directories.
SEE ALSO
bash(1)
AUTHORS
Brian Fox, Free Software Foundation
bfox@gnu.org
Chet Ramey, Case Western Reserve University
chet@po.cwru.edu
GNU Bash-4.0 1998 July 30 BASHBUG(1)