Print variables with number of iteration index in dash

Question

I work in dash and I would like to know if there is any method to print variable with index of number of iteration.

CODE :

var1="a"
var2="b"
var3="c"

tmp=0
while [ $tmp -lt 4 ]
do
    # this is how i imagine it 
    echo $('var'$tmp)  #output should be value of var$tmp
    tmp=$((tmp+1))
done

Thank you!

the `$()` is wrong there. But yes, you need to use `eval` (and run the associated security risks) to get indirect expansion in dash. — Charles Duffy, Mar 27 '17 at 16:41
BTW, you're missing quoting -- the test really should be `[ "$tmp" -lt 4 ]`, as http://shellcheck.net/ will point out. — Charles Duffy, Mar 27 '17 at 16:43
Possible duplicate of [How can I look up a variable by name with #!/bin/sh (POSIX sh)?](http://stackoverflow.com/questions/26337826/in-linux-shell-script-how-can-i-recall-value-of-variable) — Charles Duffy, Mar 27 '17 at 16:44
(argh -- I missed the "bash" in the title. `#!/bin/sh` **is not bash**, and questions about it should not be tagged or titled as bash questions). — Charles Duffy, Mar 27 '17 at 16:47

score 1 · Accepted Answer · answered Mar 27 '17 at 16:42

1

In POSIX sh, you need to use eval to perform indirect expansion:

eval "result=\$var$tmp"

Note that there are much better ways to do this in ksh, bash or other shells; see BashFAQ #6 for a comprehensive discussion of both indirect expansion and indirect assignment spanning all these shells.

answered Mar 27 '17 at 16:42

Charles Duffy

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Thank you, this helped a lot ! – SevO Mar 27 '17 at 17:02

score 0 · Answer 2 · edited May 23 '17 at 12:02

0

Using eval like below

eval "echo \"\$var${tmp}\""
# The \ escapes the $ to make it a literal dollar sign

should do it without using a third variable.

^{Note: @Charles Duffy's [ comment ] below is taken into consideration in the edit.}

edited May 23 '17 at 12:02

Community

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answered Mar 27 '17 at 16:48

sjsam

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I'm pretty staunchly against passing `eval` more than one argument -- like `ssh`, it just concatenates those arguments with whitespace to form a single string. Better to `eval "echo \"\$var${tmp}\""` -- that way we're actually *explicit* about what's going on, and won't have surprising events when your command is more involved than `echo`. – Charles Duffy Mar 27 '17 at 17:07
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(consider `eval printf '%s\n' "hello world"`, compared to `eval 'printf "%s\n" "hello world"'`, for a case-in-point example of why passing `eval` multiple arguments leads to confusion). – Charles Duffy Mar 27 '17 at 17:08

Print variables with number of iteration index in dash

2 Answers2