4 SC1067

Joachim Ansorg edited this page 2021-11-12 10:41:48 +01:00

Table of Contents

• For indirection, use arrays, declare "var$n=value", or (for sh) read/eval
• Problematic code:
• Correct code:
• Rationale:
• Exceptions:
• Related resources:

For indirection, use arrays, declare "var$n=value", or (for sh) read/eval

Problematic code:

n=1
var$n="hello"

Correct code:

For integer indexing in ksh/bash, consider using an indexed array:

n=1
var[n]="hello"
echo "${var[n]}"

For string indexing in ksh/bash, use an associative array:

typeset -A var
n="greeting"
var[$n]="hello"
echo "${var[$n]}"

If you actually need a variable with the constructed name in bash, use declare:

n="Foo"
declare "var$n=42"
echo "$varFoo"

For sh, with single line contents, consider read:

n="Foo"
read -r "var$n" << EOF
hello
EOF
echo "$varFoo"

or with careful escaping, eval:

n=Foo
eval "var$n='hello'"
echo "$varFoo"

Rationale:

var$n=value is not a valid way of assigning to a dynamically created variable name in any shell. Please use one of the other methods to assign to names via expanded strings. Wooledge BashFaq #6 has significantly more information on the subject.

Exceptions:

None

Related resources:

• Wooledge BashFaq #6: How can I use variable variables (indirect variables, pointers, references) or associative arrays?

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