Using a for loop input to rename an object within the loop in bash

Question

I am currently trying to rename an input argument by the variable "i" in the following for loop:

cd $1
num=$(echo $#)
echo $num
echo $@
echo "This is the next part where I print stuff"
for i in $(seq 2 $num)
        do
        echo $i
        echo ${!i}
        Args_array+=$(printf '${arg_%s[@]}' ${i})
        echo $Args_array
        arg_${i}=$(ls ${!i})
done

The output is as follows:

4
output_folder /path/to/my.tsv /path/to/my2.tsv /path/to/my3.tsv
2
/path/to/my.tsv
${arg_2[@]}
/var/spool/slurm/d/job6985121/slurm_script: line 23: arg_2=/path/to/my.tsv: No such file or directory

But it will not allow me to rename the $2, $3 arguments with "i" like this. Any help would be appreciated.

I want to pass these arguments into R and have to put them in arg_1, arg_2, etc. format.

Dynamic variable names are messy; why not just use a proper array? — Gordon Davisson
– Gordon Davisson, Commented Aug 1, 2022 at 23:29
@GordonDavisson I need to be able to use this function for a wide range of data inputs. My idea is that I would use the dynamic variables so that I wouldn't have to manually change my script when the number of arguments changes (which would be every time I would run the R script these arguments are being passed into. If there is a way to do that, your advice would be greatly appreciated. I am very new to coding and I am not even sure what to google at this point. Thank you again. — kaptaintrash
– kaptaintrash, Commented Aug 2, 2022 at 3:14
What is num=$(echo $#)?? Wouldn't num=$# make more sense? — David C. Rankin
– David C. Rankin, Commented Aug 2, 2022 at 7:38

markp-fuso · Accepted Answer · 2022-08-01 23:39:47Z

1

Not sure I understand what's being attempted with Args_array so focusing solely on OP's comment: 'have to put them in arg_1, arg_2' and skipping arg_1 since OP's code doesn't appear to care about storing $1 anywhere; then again, is R not capable of processing input parameters from the command line?

One bash idea:

$ cat testme
#!/usr/bin/bash

num=$#

for ((i=2;i<=$num;i++))
do
    declare args_$i=${!i}
done

for ((i=2;i<=$num;i++))
do
    typeset -p args_$i
done

Taking for a test drive:

$ testme output_folder /path/to/my.tsv /path/to/my2.tsv /path/to/my3.tsv
declare -- args_2="/path/to/my.tsv"
declare -- args_3="/path/to/my2.tsv"
declare -- args_4="/path/to/my3.tsv"

edited Aug 1, 2022 at 23:39

answered Aug 1, 2022 at 23:32

markp-fuso

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1 Comment

kaptaintrash Over a year ago

Thank you so much! Using "declare" worked. The array I am using is because I would like to pass in arguments to an R script as folllows: /Script.R ${arg_2[@]} ${arg_3[@]} ${arg_4[@]}

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