shell script to generate shell command dynamically

Question

How to generate below command dynamically for n number of elements? I don't want to use any other variable or an array.

command mycommand /path/location ${arg[1]}="${value[1]}" ${arg[2]}="${value[2]}" ...

Why don't you want to use an array? Your code already uses two of them (for no reason?). — melpomene
– melpomene, Commented Jan 12, 2019 at 13:44
In what way is this different from stackoverflow.com/q/54151974/3220113 ? And what is wrong with the answers given at https://stackoverflow.com/q/54149440/3220113 ? — Walter A
– Walter A, Commented Jan 12, 2019 at 16:35

Hielke Walinga · Accepted Answer · 2019-01-13 11:06:04Z

1

You can use a subshell with a for loop that loops over your arrays and creates the correct arguments.

command mycommand /path/location $(for ((i=0; i<"${#value[@]}"; i++)) do printf "%s=%s " "${arg[$i]}" "${value[$i]}"; done)

Like I promised in the comments, this will work even if there are spaces in the values.

Here I create the arguments dynamically and separate the arguments on null characters (\0).

I pipe these to xargs. xargs is some kind of argument parser and probably the best choice for the job.

So, instead of letting bash pass the argument (which passes them by breaking them on whitespace), we are letting xargs pass the argument and have full control on how they are splitted.

In this case I choose to separate on null characters (by setting -0), so that every other character (spaces, or even linebreaks) do not interfere with how the arguments are passed.

for ((i=0; i<"${#value[@]}"; i++)) do printf "%s=%s\0" "${arg[$i]}" "${value[$i]}"; done | 
xargs -0 command mycommand /path/location

edited Jan 13, 2019 at 11:06

answered Jan 12, 2019 at 13:51

Hielke Walinga

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3 Comments

LearningCoding Over a year ago

It is printing the command as mentioned. But value[$i] contains a string ( value[i]=" value one" ) . While executing the command shell is not treating as a single string value. for example myarg="value one" but shell is taking myarg=value only.

LearningCoding Over a year ago

I dont want print the value.. i want to pass the arguments as it is

Hielke Walinga Over a year ago

@AnjanJana You have to print it, because that is the only way to create the correct arguments dynamically. The white space in the arguments makes it a bit difficult. Currently don't have so much time, but I can look into that tomorrow. Two things I am thinking of. Include the double quotation marks in printf and execute with eval, or pipe the arguments through xargs with the --null option. You can take a look at it yourself and maybe find the solution yourself.

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