Bash: declare, assign value to a variable and call it inside a loop

Question

I am trying to declare, assign value and call variables inside a loop that runs a user defined amount of times. I would like these variables to be available after the loop. What I am trying to do is:

echo "HOW MANY ROUNDS OF TEST ITERATIONS WOULD YOU LIKE TO RUN?"
read round_nr
echo "Number of Iteration rounds set to: $round_nr!"

for r in $(seq 1 $round_nr); do
    echo "HOW MANY COLD TEST ITERATIONS DO YOU WANT IN ROUND $r?"
    read COLD$r
    echo "HOW MANY WARM TEST ITERATIONS DO YOU WANT IN ROUND $r?"
    read WARM$r
    echo "HOW MANY HOT TEST ITERATIONS DO YOU WANT IN ROUND $r?"
    read HOT$r
    echo "HOW MANY NR OF FIXES PER TEST ITERATION $r?"
    read NUMFIX$r
    echo "ITERATION $r INPUT VALUES: COLD/WARM/HOT/NUMFIX:"
    echo $COLD$r $WARM$r $HOT$r $NUMFIX$r
done

In that way for every loop (in a user defined set of round_nr loops) four variables will be created and assigned user input values. I am planning to use these variables later on.

Many thanks for the help!

chepner · Accepted Answer · 2013-03-06 16:44:00Z

2

You can indeed use declare, but it will be a lot easier to use an array. (I use the -p flag for read to save space here; you don't need to use it.)

for r in $(seq 1 $round_nr); do
    read -p "HOW MANY COLD TEST ITERATIONS DO YOU WANT IN ROUND $r?" ans
    declare "COLD$r=$ans"
    read -p "HOW MANY WARM TEST ITERATIONS DO YOU WANT IN ROUND $r?" ans
    declare "WARM$r=$ans"
    read -p "HOW MANY HOT TEST ITERATIONS DO YOU WANT IN ROUND $r?" ans
    declare "HOT$r=$ans"
    read -p "HOW MANY NR OF FIXES PER TEST ITERATION $r?" ans
    declare "NUMFIX$r=$ans"
    echo "ITERATION $r INPUT VALUES: COLD/WARM/HOT/NUMFIX:"

    # Here's the tricky part. It's easier to create the variable than it
    # is to use it.
    varcold="COLD$r"
    varwarm="WARM$r"
    varhot="HOT$r"
    varnumfix="COLD$r"

    echo ${!varcold} ${!varwarm} ${!varhot} ${!varnumfix}
done

With an array, it's simply

for r in $(seq 1 $round_nr); do
    read -p "HOW MANY COLD TEST ITERATIONS DO YOU WANT IN ROUND $r?" cold[r]
    read -p "HOW MANY WARM TEST ITERATIONS DO YOU WANT IN ROUND $r?" warm[r]
    read -p "HOW MANY HOT TEST ITERATIONS DO YOU WANT IN ROUND $r?" hot[r]
    read -p "HOW MANY NR OF FIXES PER TEST ITERATION $r?" numfix[r]
    echo "ITERATION $r INPUT VALUES: COLD/WARM/HOT/NUMFIX:"
    echo ${cold[r]} ${warm[r]} ${hot[r]} ${numfix[r]}
done

In either case, the variables will all be available after the for loop, as long as you don't do anything to make the for loop run in a subshell (like put it in a pipeline or enclose it in (...), etc.)

answered Mar 6, 2013 at 16:44

chepner

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6 Comments

Nikl Over a year ago

Thank you so much for explaining this, both work great, and I 've learned smth new!!

Nikl Over a year ago

I have an additional question, this piece of code works very well if i run it independently but once I embed it in my script it returns a ¨read: cold[r]: bad variable name¨ error once it reaches the read part, still inside the loop. It is not run in any subshell or pipe, enclosed in brackets etc. Do you have any idea what the problem might be?

Nikl Over a year ago

:That is when I run the array solution.

chepner Over a year ago

Do you have #!/bin/bash at the top of your script? If not, you may be running your script with sh, which doesn't support arrays.

Nikl Over a year ago

I think I had some other typo somewhere in my script. I re-wrote and works great. Many thanks!

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Carl Norum · Accepted Answer · 2013-03-06 16:24:35Z

0

You can use an array (probably the preferred method), or you could do some eval gymnastics. The bash man page has everything you need to know to do either.

answered Mar 6, 2013 at 16:24

Carl Norum

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