Variable Redirect in bash vs. ksh

Question

I found this script:

#!/bin/bash

readvar () {
    while read -r line
    do
            declare "$line"
    done < "$1"
    echo ${!2}
}

Over here: Bash Read Array from External File

I have a file called test.txt:

_127_0_0_1=kees

If I do in bash:

readvar ./test.txt _127_0_0_1

I get the output:

kees

However if I do the same thing in ksh, (Declare doesn't work in ksh so I replaced it with typeset.) :

#!/bin/ksh

readvar () {
    while read -r line
    do
            typeset "$line"
    done < "$1"
    echo ${!2}
}

readvar ./test.txt _127_0_0_1

I get the output:

$ ./test.sh

./test.sh: syntax error at line 8: `2' unexpected Segmentation fault: 11

Why is that ? And how can I make it work in ksh? (ksh93 for that matter)

$ ksh --version version sh (AT&T Research) 93u 2011-02-08

azbc
– azbc

2017-03-25 22:21:30 +00:00
Commented Mar 25, 2017 at 22:21 — azbc
– azbc, Commented Mar 25, 2017 at 22:21

Henk Langeveld · Accepted Answer · 2017-03-27 13:30:35Z

2

Here's man ksh:

   ${!vname}
          Expands to the name of the variable referred to by vname.  
          This will be vname except when vname is a name reference.

As you can see, this is completely different from what bash does.

For indirection in ksh, you can use nameref (an alias for typeset -n):

foo() {
  bar=42
  nameref indirect="$1"
  echo "$indirect"
}
foo bar

edited Mar 27, 2017 at 13:30

Henk Langeveld

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answered Mar 25, 2017 at 23:24

that other guy

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2 Comments

azbc Over a year ago

#!/bin/ksh  foo() {  while read -r line     do             typeset "$line"     done < "$1"    nameref indirect="$2"   echo "$indirect" }  foo ./test.txt _127_0_0_1

input test.txt: _127_0_0_1=kees output: kees

l'L'l Over a year ago

@azbc: Another convenient function of setting nameref in ksh is you can also change it's value (eg. eval "${!indirect}=foobar") ... echo "${!indirect}=${indirect}"

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