SH: Recursive Variable Substitution

TVT · 07-01-2010, 07:41 AM

Hi!

I have the following test code fragment:

Code:

#! /bin/sh

A1='ZZZ'

B='A'
N='1'

if [ "${$B$N}" == 'ZZZ' ]; then echo 'OK'; fi

When I try to run it 'sh' reports the following message^

Code:

test.sh: ${$B...}: Bad substitution

You might understand what I mean with that test code so could you recommend how to achieve the required effect?

Guttorm · 07-01-2010, 08:49 AM

Hmm. I think you are looking for eval.

Code:

A1="ZZZ"
V1="A"
V2="1"
VARNAME="$V1$V2"
eval VALUE=\$$VARNAME
echo $VALUE

TVT · 07-01-2010, 09:21 AM

Quote:

Originally Posted by Guttorm

Hmm. I think you are looking for eval.

Code:

A1="ZZZ"
V1="A"
V2="1"
VARNAME="$V1$V2"
eval VALUE=\$$VARNAME
echo $VALUE

YES but how to elegantly use your way with 'if' statement?

grail · 07-01-2010, 09:27 AM

You could possibly go one line less too:

Code:

A1="ZZZ"
V1="A"
V2="1"
eval VARNAME="$V1$V2"
echo ${!VARNAME}

Just an alternative at the end their for indirect

Edit: Use the "if" instead of "echo" line

TVT · 07-01-2010, 12:57 PM

Quote:

Originally Posted by grail

You could possibly go one line less too:

Code:

A1="ZZZ"
V1="A"
V2="1"
eval VARNAME="$V1$V2"
echo ${!VARNAME}

Just an alternative at the end their for indirect

Edit: Use the "if" instead of "echo" line

Doesn't seem to solve the difficulty:

Code:

$ sh -x test1.sh
+ A1=ZZZ
+ V1=A
+ V2=1
+ eval VARNAME=A1
+ VARNAME=A1
test1.sh: ${!V...}: Bad substitution

unSpawn · 07-01-2010, 01:35 PM

Quote:

Originally Posted by TVT

Doesn't seem to solve the difficulty

Is your shell by any chance a "true" Bourne Shell?

TVT · 07-01-2010, 03:09 PM

Quote:

Originally Posted by unSpawn

Is your shell by any chance a "true" Bourne Shell?

No. My shell is just ordinary /bin/sh shell (see message title). This is because some systems do not have bash by default.

tuxdev · 07-01-2010, 03:30 PM

Quote:

No. My shell is just ordinary /bin/sh shell (see message title). This is because some systems do not have bash by default.

Just because it's /bin/sh doesn't give *any* information on whether it's a actual legacy Bourne shell or a POSIX shell. Please verify that it really is POSIX, not Bourne.