Shell scripting : how to name a variable with the value of another variable

JimOrJoe · 06-11-2008, 08:50 PM

Hi, there:

I have to name a new variable with the value of another variable, then give the new variable a value and export it. Could anyone please give me some sample shell scripts?

To clarify the scenario for those who did not comprehend the above description, here is the elaboration:

In a shell script, I received a argument, say varName. Its value is a random string. Let's take it for granted that the string is "slip", how do I delcare a variable using varName intead of scripting slip="pink"?

Thanks and Cheers

Joe

osor · 06-11-2008, 08:59 PM

man 1 eval

ghostdog74 · 06-11-2008, 09:27 PM

Use arrays instead, if you are using bash, or other shells that supports arrays.

osor · 06-11-2008, 09:34 PM

Quote:

Originally Posted by ghostdog74

Use arrays instead, if you are using bash, or other shells that supports arrays.

I don’t think the OP’s situation can be done with arrays (although I may be wrong). I think he or she wants a simple:

Code:

eval $varName=pink

Of course usually code which requires the use of eval may have potential for better overall design, but sometimes it’s convenient.

ghostdog74 · 06-11-2008, 10:12 PM

Quote:

Originally Posted by osor

I don’t think the OP’s situation can be done with arrays (although I may be wrong). I think he or she wants a simple:

Code:

eval $varName=pink

Of course usually code which requires the use of eval may have potential for better overall design, but sometimes it’s convenient.

just my thoughts unless i really misinterpret the requirement. Whether naming a variable with the name of another or not, eventually, all we want to do is to allocate memory, because variables are just memory locations. Using arrays is analogous (whatever that word's spelling is

) to that. So at first if var="slip", it could be a[0]="slip". then $var$Name="pink" , it could be a[1]="pink". although it would be nicer if the tool support associative arrays. $0.02

JimOrJoe · 06-11-2008, 10:15 PM

with eval, I found out how to read from a variable with a random name like this:

foo=10 randomVarName=foo
eval y='$'$randomVarName
echo $y
10

The question is how to set value to the variable with a random name:

randomVarName=foo
eval y='$'$randomVarName
?
echo $y
what should i do to give a value to $foo at line "?"

Thanks

Hko · 06-12-2008, 06:02 AM

Quote:

Originally Posted by JimOrJoe

with eval, I found out how to read from a variable with a random name like this:

foo=10 randomVarName=foo
eval y='$'$randomVarName
echo $y
10

Another way (bash only):

Code:

foo=10
randomVarName=foo
y=${!randomVarName}
echo $y

Quote:

Originally Posted by JimOrJoe

The question is how to set value to the variable with a random name

Code:

randomVarName=foo
eval $randomVarName=123
echo $foo

unSpawn · 06-12-2008, 06:38 AM

Quote:

Originally Posted by Hko

Code:

y=${!randomVarName}

It's clean, utterly incompatible, I like that ;-p

Two evals goooohhhd, four evals baaahhhhd!

Hko · 06-12-2008, 10:08 AM

Quote:

Originally Posted by unSpawn

It's clean, utterly incompatible, I like that ;-p

True, just like C++ is incompatible with Fortran.
:-)

JimOrJoe · 06-15-2008, 09:36 PM

Thanks a lot mentors, you have answered my question