[SOLVED] PATH Variables: Ergonomic Assignment Dilemma

andrew.comly · 11-18-2015, 11:20 PM

To "/" or not to "/".

I have a dilemma over assigning variables for the following shellscript backup program:

Code:

#!/bin/bash


#VARIABLES
	#Initialize
		unset BOOT DISK0 DISK1 DISK2 SOURCE TARGET1 TARGET2 USER
	
	#Define
		#Individual
			DISK0=/Sea_ext4
			DISK1=/Sea_ntfs
			DISK2=/Sam_HM320II
			USER=/$(echo $(whoami))

		#Composite
			SOURCE=/media${USER}${DISK0}/recent
			TARGET1=/media${USER}${DISK1}/recent
			TARGET2=/media${USER}${DISK2}/recent
		

#CORE DATA
	#Synchronization
		rsync -Savi -Eu -stat --delete ${SOURCE}/AC ${TARGET1};
		rsync -Savi -Eu -stat --delete ${SOURCE}/AC ${TARGET2};

When assigning the variables above, should I include the "/", e.g.

Code:

	DISK1=/Sea_ntfs
	DISK2=/Sam_HM320II

or not, e.g.

Code:

	DISK1=Sea_ntfs
	DISK2=Sam_HM320II

This may seem like an extremely small insignificant matter, but when you include the "/" in the pathname, than
1) in the next section Composite Variables, than you have to look at a morass of several variables lumped together, "/" included; e.g.

Code:

		SOURCE=/media${USER}${DISK0}/recent
		TARGET1=/media${USER}${DISK1}/recent

rather than "/" excluded; e.g.

Code:

		SOURCE=/media/${USER}/${DISK0}/recent
		TARGET1=/media/${USER}/${DISK1}/recent

2) in the main code, you have pathnames starting out without any "/", e.g.

Code:

	rsync -Savi -Eu -stat --delete ${SOURCE}/AC ${TARGET1};

rather than "/" excluded from the individual path name variables; e.g.

Code:

	rsync -Savi -Eu -stat --delete /${SOURCE}/AC /${TARGET1};

With the colorized themes that most IDEs provide, seeing a different colored "/"
1) between the two variables
2) before pathnames
can make the code more clear, and can make the usual boring morass become alive.

Is there some programming board/standard (e.g. POSIX) that advises programmers of a standard of whether or not to include the "/" in the Individual Variable names?

zhjim · 11-19-2015, 02:40 AM

Dunno if there is any standard but I say its more preference or liking that any thing much else.
As for compatibility reasons I would never use absolute path names only relatives. And if you have to use absolute path try to use a variable for this. And within the actual script only have relative ones. Something like

Quote:

root="/var/www"
logs="logs"
upload="upload"
mv "$root/$upload" "$root/$upload/old"

This way you can move the script to another server and just have to adjust root variable. Also you still have "morass"...
I think BASH is bad for reading these kind of things. But php for example is a bit nicer and more clearly to read

Quote:

$root="/var/www"
$logs="logs"
$upload="upload"
cmd="mv $root .'/'. $upload $root .'/'. $upload .'old'

The main reason why I would never use / at the start of a path is that / is the root on linux systems. This way if you forget to set any path variable before this you end up starting with / for your path. This can be troublesome and might lead to some exploits even.

NevemTeve · 11-19-2015, 03:23 AM

The name of the variable should describe the content (except for vairable 'USER': it is usually preset and no to be played with):

Code:

DISK_LABEL=DORINA
DISK_PATH="/dev/disk/by-label/$DISK_LABEL"