[SOLVED] Another option besides 'expr'

DennyY · 08-31-2019, 11:07 AM

Hi,

Just wondering if there is another option besides using 'expr' for this code?

Thank you for your help,
Denny

Code:

#!/bin/bash

count=0
num=10
while [ $count -lt 10 ]
do
        echo
        echo $num seconds left to stop this process $1
        echo
        sleep 1

num=`expr $num - 1`
count=`expr $count + 1`
done
echo
echo $1 process is stopped!!!
echo

Firerat · 08-31-2019, 11:16 AM

you could try

Code:

((count++))

or, a for loop

Code:

for ((count=0;count<10;count++));do
     <stuff>
done

edit
since you are counting down

Code:

for ((count=10;count>0;count--));do
     printf "%s\r" "$count seconds left to stop this process $1 "
     sleep 1 # forgot this in first edit
done
printf "\n" # \n is new line, \r was return ( to start of line )

untested, but that should just update the line instead of making new ones each time
I have been lazy with the printf, really you should split it up.

michaelk · 08-31-2019, 11:29 AM

or

Code:

for ((i = 10 ; i > 0 ; i--)); do
  echo "Seconds left: $i"
  sleep 1
done

I missed your updated post...

rnturn · 08-31-2019, 11:39 AM

Quote:

Originally Posted by DennyY

Hi,

Just wondering if there is another option besides using 'expr' for this code?

Others have already noted the use of the bash "(( expression ))" syntax for math expressions.

Another alternative you might consider is losing the backticks:

Code:

$( command )

instead of

Code:

`command`

Backticks are darned hard to see and the newer syntax is much easier to spot and allows smarter editors (vim, emacs, etc.) that highlight opening/closing brackets, braces, and parentheses to indicate those expressions---especially when you've forgotten to close an expression in one of those characters. I've never been able to figure out a way of nesting expressions within expressions using backticks, either. The person who has to read your code in six months (and that might be you) will love you for abandoning the backticks.

HTH...

MadeInGermany · 08-31-2019, 12:07 PM

If portability matters, use $(( )) that is a (arithmetic) expression and works in all Posix-compatible shells.
In contrast, the (( )) is a (arithmetic) command, and only works in bash, ksh, zsh.
With $(( )) there is a one-to-one translation from expr

Code:

count=`expr $count + 1`

translates to

Code:

count=$(($count + 1))

expr is itself a command, its arguments are expanded by the shell unless \escaped

Code:

mult=`expr $count \* 2`

translates to

Code:

mult=$(($count * 2))

More advanced stuff:
Within $(( )) you can omit the $ in front of variables, because any letter-word MUST be a variable. Also spaces can be omitted.

Code:

count=$((count+1))

But the $ is still required in case you use variable modifiers, for example

Code:

count=$((${count:-0} + 1))

I guess the (( )) will make it into the next Posix standard... whenever that will be.