[SOLVED] linux bin and bash

mhsahkir · 12-29-2014, 06:34 AM

hi i am linux beginner stage can somebody easily explain what is /bin/bash. another question what is the different "shutdown -h now" "poweroff"?

jpollard · 12-29-2014, 06:52 AM

1. In short, /bin/bash is the path to an executable. The bash executable is a command interpreter using a simple terminal line interface. It is also very easy to use script files that contain command lines to create simple applications.

2. Not much. The shutdown command provides more flexibility than the poweroff command. Most distributions have the poweroff command linked to the shutdown command - which in turn may be linked to yet another. But the purpose of the power off is the same as "shutdown -P -h now", and if the shutdown (which may be a script) will use the name it was invoked by to identify a predefined set of options. It is also possible that the poweroff is linked to a "halt" utility - which should only be used for emergencies, as the halt utility directly is intended to halt the system immediately. On Slakware, the halt utility (or poweroff) will first verify that the system is in single user mode before halting/poweroff the system - instead, it will invoke the shutdown utility with the appropriate options to gracefully shutdown the system, then either halt or power off.

John VV · 12-29-2014, 02:19 PM

in a script that "/bin/bash" on the top line should be preceded with a #!

Code:

#!/bin/bash
----- or this ----
#!/bin/sh
----- or this ----
#!/bin/csh
---- or even this for python code-------
#!/usr/bin/env python

google " shebang linux "
https://en.wikipedia.org/wiki/Shebang_%28Unix%29

jpollard · 12-29-2014, 04:48 PM

Quote:

Originally Posted by John VV

in a script that "/bin/bash" on the top line should be preceded with a #!

Code:

#!/bin/bash
----- or this ----
#!/bin/sh
----- or this ----
#!/bin/csh
---- or even this for python code-------
#!/usr/bin/env python

google " shebang linux "
https://en.wikipedia.org/wiki/Shebang_%28Unix%29

To be a bit more specific, the first line of a script file that is marked as executable should/must start with "#!" followed by the path to the program (or script even) that is to interpret the contents.

This is not, however, a property of a script - it is the property of the kernel validating a file for execution - and when the "#!" is found, using the rest of the line interpreted as the command (with options) to interpret the file.

veerain · 12-29-2014, 09:02 PM

Every system has a root directory which holds all files and sub directories. Root is give the symbol /. Bin is a subdirectory called simply as bin and if given together with root as /bin. bash is executable file located in bin directory. So it's refered as /bin/bash. The / acts as separator for directories and files.

As for commands shutdown poweroff halt just use safe ones for now. And if you want to know more details you can read their man pages by:

Code:

man shutodwn
man poweroff
man halt

mhsahkir · 01-06-2015, 06:25 AM

Thank you guys for your kind reply i really appreciated.

maples · 01-06-2015, 07:54 AM

Quote:

Originally Posted by jpollard

It is also possible that the poweroff is linked to a "halt" utility - which should only be used for emergencies, as the halt utility directly is intended to halt the system immediately.

Well, then I guess I should stop using "halt -p" to shutdown my Debian system.

jpollard · 01-06-2015, 09:25 AM

It can depend on the system. Some will check to see if it is already in single user mode, THEN it will halt.

If it is in multi-user mode then it will shutdown the system gracefully.

But it is always better to not depend on that - it causes some bad habits that can cause problems in a multi-vendor site (and not just Linux either - UNIX can also have variations).