How to access further members of an array when using bash variable indirection?

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bash bash-expansion bash-array indirection

                          Consider the following example, it seems it's working fine with the index 0:

    $ a1=(1 2 3)
    $ a2=(a b c)
    $ for x in a1 a2; do echo "${!x}"; done
    1
    a
    $ for x in a1 a2; do echo "${!x}"; done
    1
    a

However with the index 1 it prints nothing:

    $ for x in a1 a2; do echo "${!x}"; done    
    
    
Arrays just by themselves are fine:

    $ echo "${a1} ${a2}"
    2 b

### Edit - A real life use case based on *ilkkachu* answer

    SHIBB=(https://shibboleth.net/downloads/service-provider/3.0.2/  shibboleth-sp-3.0.2 .tar.gz)
    XERCES=(http://apache.mirrors.nublue.co.uk//xerces/c/3/sources/  xerces-c-3.2.1 .tar.gz)
    XMLSEC=(http://apache.mirror.anlx.net/santuario/c-library/  xml-security-c-2.0.1 .tar.gz)
    XMLTOOL=(http://shibboleth.net/downloads/c++-opensaml/latest/  xmltooling-3.0.2 .tar.gz)
    OPENSAML=(http://shibboleth.net/downloads/c++-opensaml/latest/  opensaml-3.0.0 .tar.gz)
    
    typeset -n x
    for x in XERCES XMLSEC XMLTOOL OPENSAML SHIBB; do
      url="${x}" app="${x}" ext="${x}"
      [ -f "./${app}${ext}" ] || wget "${url}${app}${ext}"
      tar -xf "./${app}${ext}"
      cd "./${app}" && ./configure && make -j2 && make install && ldconfig
      cd ..
    done
                        

Asked by NarūnasK (2525 rep)

Sep 4, 2018, 08:03 PM
Last activity: Oct 15, 2018, 08:03 PM

How to access further members of an array when using bash variable indirection?

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