Sponsored Content
Top Forums Shell Programming and Scripting What does this do in bash: ${pid:-} Post 302245955 by mindOnMy$ on Sunday 12th of October 2008 01:49:16 AM
Old 10-12-2008
Question What does this do in bash: ${pid:-}

As i understand it, this means
if pid is
a) unset, or
b) set to null
then replace with the value on the right of the minus sign--which is null

This confuses me because
a) I thought if a variable isn't set to anything it's automatically null. If not then what is an uninitiated variable set to?
b) if the variable is already set to null, then why replace it with another null?

I see this on line 74 in the file /lib/lsb/init-functions (I'm using hardy heron ubuntu)
Here's an excerpt from the file:
Code:
if [ -z "${pidfile:-}" ]; then 
    pidfile=/var/run/${1##*/}.pid 
fi

 

10 More Discussions You Might Find Interesting

1. Programming

printing ppid,child pid,pid

question: for the below program i just printed the value for pid, child pid and parent pid why does it give me 6 values? i assume ppid is 28086 but can't figure out why there are 5 values printed instead of just two! can someone comment on that! #include<stdio.h> #define DIM 8 int... (3 Replies)
Discussion started by: a25khan
3 Replies

2. Shell Programming and Scripting

how to get PID only

The below command returns full line.How can i get only PID from this line ie 15794 from the below example (FI NY) nbswpsa52.ny.ficc.gs.com~ ->ps -ef | grep keepalive | grep -v keepaliveStub | grep -v swapback | grep -v grep ficctprd 15794 1 0 13:12:58 ? 0:01 keepalive (3 Replies)
Discussion started by: kotasateesh
3 Replies

3. Shell Programming and Scripting

PID in BASH

In a shell script, in need to execute a proccess in background, do some jobs then kill that process. ie, someproc parameter1 & somescript.sh kill pid_of_the_proc_in_the_first_line How can can get the PID of the process I'm invoking in the first line? (1 Reply)
Discussion started by: rayne
1 Replies

4. UNIX for Dummies Questions & Answers

Session PID & socket connection pid

1. If I use an software application(which connects to the database in the server) in my local pc, how many PID should be registered? Would there be PID for the session and another PID for socket connection? 2. I noticed (through netstat) that when I logged in using the my software application,... (1 Reply)
Discussion started by: pcx26
1 Replies

5. Shell Programming and Scripting

KILL PID, intern should kill another PID.

Hi All, In my project i have two process runs in the back end. Once i start my project, and execute the command ps, i get below output: PID TTY TIME CMD 9086 pts/1 0:00 ksh 9241 pts/1 0:02 java 9240 pts/1 0:00 shell_script_bg java with 9241 PID is the main... (4 Replies)
Discussion started by: rkrgarlapati
4 Replies

6. UNIX for Dummies Questions & Answers

Need to get pid of a process and have to store the pid in a variable

Hi, I need to get the pid of a process and have to store the pid in a variable and i want to use this value(pid) of the variable for some process. Please can anyone tell me how to get the pid of a process and store it in a variable. please help me on this. Thanks in advance, Amudha (7 Replies)
Discussion started by: samudha
7 Replies

7. UNIX for Dummies Questions & Answers

Get pid

Hello people, This question might seem to be a little naive but here it goes: I want to know the PID of a script that is running in the background. eg: There is a script called Data_Downloader.sh I am using the command: ps -ef | grep Data_Downloader.sh But I am getting the output as wrkarea... (9 Replies)
Discussion started by: Rajat
9 Replies

8. UNIX for Dummies Questions & Answers

Another PID ?

I have searched to find an anwer to no avail, I hope you can help me. I have a.ksh that many people call and a.ksh calls b.ksh b.ksh is also invoked stand-alone by many people as well In b.ksh I want to do something different if it was not involked by a.ksh. How can I do this? (7 Replies)
Discussion started by: CAGIRL
7 Replies

9. UNIX for Dummies Questions & Answers

Write pid and command name to a txt file while executing a bash script

Hi All, Just have a requirement, I am executing a bash shell script, my requirement is to catch the pid and job name to a txt file in the same directory, is there anyway to do it? please help me out. Regards Rahul ---------- Post updated at 08:42 AM ---------- Previous update was at... (2 Replies)
Discussion started by: rahulkalra9
2 Replies

10. UNIX for Dummies Questions & Answers

Login PID in sh/bash different

In bourne shell the PID generated for the command "ps" matches my login id PID in the command "who -Hu" but in bash/linux the PID generated with the same commands are different . Why so? (2 Replies)
Discussion started by: asd78in
2 Replies
LIBBASH(7)							  libbash Manual							LIBBASH(7)

NAME
libbash -- A bash shared libraries package. DESCRIPTION
libbash is a package that enables bash dynamic-like shared libraries. Actually its a tool for managing bash scripts whose functions you may want to load and use in scripts of your own. It contains a 'dynamic loader' for the shared libraries ( ldbash(1)), a configuration tool (ldbashconfig(8)), and some libraries. Using ldbash(1) you are able to load loadable bash libraries, such as getopts(1) and hashstash(1). A bash shared library that can be loaded using ldbash(1) must answer 4 requirments: 1. It must be installed in $LIBBASH_PREFIX/lib/bash (default is /usr/lib/bash). 2. It must contain a line that begins with '#EXPORT='. That line will contain (after the '=') a list of functions that the library exports. I.e. all the function that will be usable after loading that library will be listed in that line. 3. It must contain a line that begins with '#REQUIRE='. That line will contain (after the '=') a list of bash libraries that are required for our library. I.e. every bash library that is in use in our bash library must be listed there. 4. The library must be listed (For more information, see ldbashconfig(8)). Basic guidelines for writing library of your own: 1. Be aware, that your library will be actually sourced. So, basically, it should contain (i.e define) only functions. 2. Try to declare all variables intended for internal use as local. 3. Global variables and functions that are intended for internal use (i.e are not defined in '#EXPORT=') should begin with: __<library_name>_ For example, internal function myfoosort of hashstash library should be named as __hashstash_myfoosort This helps to avoid conflicts in global name space when using libraries that come from different vendors. 4. See html manual for full version of this guide. AUTHORS
Hai Zaar <haizaar@haizaar.com> Gil Ran <ril@ran4.net> SEE ALSO
ldbash(1), ldbashconfig(8), getopts(1), hashstash(1) colors(1) messages(1) urlcoding(1) locks(1) Linux Epoch Linux
All times are GMT -4. The time now is 04:36 PM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy