Bash script variables assignment syntax question

[emily22]

hey there to all!

I'm writing a bash script and I wonder what is the correct syntax for arithmetic expression when it comes to integers which are stored in variables.

For example

aa=23
bbb=35
cccc=479

and I want to assign:

dd=$(($aa+$bbb))

or

aa=$(($aa+$bbb))

or

ee=$(($cccc-$aa))

Is this correct or let is working better?

[musher0]

Hello!

I know it is never wrong to put a 'let' statement before this type of variable, although it takes an extra 4 bytes.

Best of luck.

[sunburnt]

Hi emily22; "Let" is kinda diminished, or depreciated as it were ( not used ).

I can`t remember the forum name of the competent member that showed me this:

Code: Select all

aa=23 ; bbb=35

((dd=$aa+$bbb))

echo $dd

[jpeps]

Hi emily22; "Let" is kinda diminished, or depreciated as it were ( not used ).

I can`t remember the forum name of the competent member that showed me this:

Code: Select all

aa=23 ; bbb=35

((dd=$aa+$bbb))

echo $dd

works, but what's wrong with dd=$(($aa + $bbb)) ?

[amigo]

'$((dd=$aa+$bbb))' would be the most portable among different shells. 'let' is bash-specific. While '((dd=$aa+$bbb))' works with bash, it may not with other shells. Whitespace around the operators has o effect.

[musher0]

Hello.

Even if the "let" statements are officially deprecated, the following script does not work if the "let" statements are removed.

Code: Select all

#!/bin/sh
# ~/$MAPPS/bin/urxvt-fordo-cascade-4.sh
####
# Ce script-ci doit demeurer en l'état.
# (c) Christian L'Écuyer, Gatineau (Qc), Canada, janvier 2012. Gratuiciel, mais tous droits réservés.
# Courriel : http://scr.im/reyucelc
#
# Si ça ne marche pas, assurez-vous qu'un autre "rxvt" ne tourne pas quelque part en mémoire.
####
if [ "`pidof rxvt`" != "" ];then
	for i in `seq 4`;
	do
		wmctrl -c Console
	done
	exit
	else	
		export gm="g 80x16"
		let x=45
		let y=80
		for i in `seq 4`;
	        do
	                rxvt -bd grey10 -b 4 -fg white -cr green -sr +st +tcw -bc -tint black -sh 57 -T "Console $i" -$gm-$x-$y & 
			let x=$x+120
			let y=$y+170
			sleep 0.17s
	        done 
fi

Is it me, bash (version 4.1.0-1_i686, 2009), my computer, my Puppy version (lupu 5.25 retro4), my attitude towards life, a spell from my ex? Someone has an explanation? Thanks in advance.

Also, before you ask, I have found a reason to open 4 console windows at the same time!

BFN.

[sunburnt]

musher0;

Code: Select all

x=45 ; y=80
........
((x=$x+120)) ; ((y=$y+170))

[Peterm321]

For example

aa=23
bbb=35
cccc=479

and I want to assign:

dd=$(($aa+$bbb))

Code: Select all

#!/bin/bash
aa=23
bbb=35
cccc=479 
let dd=aa+bbb
echo -e "\ndd= $dd\n"

[technosaurus]

Hello.

Even if the "let" statements are officially deprecated, the following script does not work if the "let" statements are removed.

...

Is it me, bash (version 4.1.0-1_i686, 2009), my computer, my Puppy version (lupu 5.25 retro4), my attitude towards life, a spell from my ex? Someone has an explanation? Thanks in advance.

Also, before you ask, I have found a reason to open 4 console windows at the same time!

BFN.

see amigo's post for portable, alternative syntax

[Shep]

I can`t remember the forum name of the competent member that showed me this:

Code: Select all

aa=23 ; bbb=35

((dd=$aa+$bbb))

echo $dd

Inside $((....)) bash allows you to omit the $ preface to all the variables:

a=24 b=56 c=$((a+b)); echo $c
80

[musher0]

Thanks to all for their answers.

[sunburnt]

Shep; You`re right of course, I was winging it from memory.
So...

((dd=aa+bb))

[jpeps]

Shep; You`re right of course, I was winging it from memory.
So...

((dd=aa+bb))

interesting; I'd never tried that before. Just goes to prove that $$ is dispensable.