Score:0

Ubuntu

Using variables in for loops bash

Yunfei Chen

11/1/22, 11:30 PM

I was just wondering if it is possible to use variables in for loops?? I tried:

for number in { eval echo {0..$1}}
do 
    echo 5
done

I meant for it to print out 5 the number of times I entered into the prompt however, it acts strangely if I enter in:

./test.sh 2

It should print out 5 two times, but it prints out 5 four times. Can someone help me with this? And also why is it printing out 4 times instead of 2??

Edit: For the most part

for number in $(seq "$2")

Works but If I try a calculation with it, it breaks my code:

time=1
total=5
for number in $(seq "$2")
do
    echo "$time + $total" | bc
done

Gives: seq: invalid floating point argument: ‘’ Try 'seq --help' for more information. Can someone tell me how to fix it??

1 + 2

bash

ubfan1

11/1/22, 11:54 PM

Use backtics (`) instead of the outer { } and your loop should work, but start at 1 instead of 0 for your expected two times through the loop.

steeldriver

11/2/22, 3:12 AM

If you use `seq "$2"` then you need to provide a numeric 2nd positional parameter when you call the script ex. `./test.sh foo 2`

Score:2

Ubuntu

steeldriver

11/1/22, 11:42 PM

It prints out 5 four times because { eval echo {0..2}} results in four whitespace-separated tokens {, 0, 1 and 2}

If you want to use $1 as the end of a range expression in bash, it's better to use the external seq command:

for number in $(seq "$1")

or use a C-style for loop

for ((number=0; number<"$1"; number++))

0 + 5

Yunfei Chen

11/2/22, 2:09 AM

It works but If I use variables inside of the for loop it breaks immediately

Yunfei Chen

11/2/22, 2:09 AM

time=1 total=5 for number in $(seq "$2") do echo "$time + $total" | bc done

steeldriver

11/2/22, 2:15 AM

@YunfeiChen fails how, exactly? How are you calling the script? In particular, how many positional parameters are you supplying (since you apparently changed `$1` to `$2`)

Yunfei Chen

11/2/22, 4:56 PM

Gives me:(standard_in) 1: syntax error (standard_in) 1: illegal character: : (standard_in) 1: syntax error (standard_in) 1: syntax error (standard_in) 1: syntax error (standard_in) 2: syntax error (standard_in) 2: illegal character: : (standard_in) 2: syntax error (standard_in) 2: syntax error (standard_in) 2: syntax error

steeldriver

11/2/22, 5:21 PM

@YunfeiChen comments are not the right place for follow-on questions - in particular, the formating doesn't allow me to see what you are actually typing. If the "illegal character" is `^M` then that's because your script has Windows line endings.

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: Using variables in for loops bash

TH: การใช้ตัวแปรในการวนรอบ bash

RO: Utilizarea variabilelor în buclele for bash

RU: Использование переменных в циклах for bash

VI: Sử dụng các biến trong vòng lặp for bash

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