Test if parameter is set

Test if parameter is set

[Thorsten Kampe]

Hi,

how can I test if a parameter is set?

Like in...

if $VAR_IS_SET; then
    print Variable is set
else
    print Variable is not set
fi

Thorsten

Re: Test if parameter is set

[Frank Terbeck]

Thorsten Kampe wrote:
> how can I test if a parameter is set?
>
> Like in...
>
> if $VAR_IS_SET; then
>     print Variable is set
> else
>     print Variable is not set
> fi

In zsh:

if (( ${+parameters[foo]} )); then
   : set
else
   : unset
fi


In POSIX shells:

if [ x${foo+set} = xset ]; then
   : set
else
   : unset
fi

Regards, Frank

-- 
In protocol design, perfection has been reached not when there is
nothing left to add, but when there is nothing left to take away.
                                                  -- RFC 1925

Re: Test if parameter is set

[Stephane Chazelas]

2011-04-19 18:48:57 +0200, Thorsten Kampe:
> Hi,
> 
> how can I test if a parameter is set?
> 
> Like in...
> 
> if $VAR_IS_SET; then
>     print Variable is set
> else
>     print Variable is not set
> fi
[...]

if (($+VAR))

or portably:

if [ -n "${VAR+x}" ]

-- 
Stephane

Re: Test if parameter is set

[Peter Stephenson]

On Tue, 19 Apr 2011 18:48:57 +0200
Thorsten Kampe <thorsten@thorstenkampe.de> wrote:
> how can I test if a parameter is set?

if (( ${+VAR} )); then
   ...

is the zsh-specific answer.  However, you can do this in a more standard
way, should you wish, with

if [[ -n ${VAR+1} ]]; then
   ...

(note no ":").

-- 
Peter Stephenson <pws@csr.com>            Software Engineer
Tel: +44 (0)1223 692070                   Cambridge Silicon Radio Limited
Churchill House, Cambridge Business Park, Cowley Road, Cambridge, CB4 0WZ, UK


Member of the CSR plc group of companies. CSR plc registered in England and Wales, registered number 4187346, registered office Churchill House, Cambridge Business Park, Cowley Road, Cambridge, CB4 0WZ, United Kingdom

Re: Test if parameter is set

[Peter Stephenson]

On Tue, 19 Apr 2011 18:26:41 +0100
Peter Stephenson <Peter.Stephenson@csr.com> wrote:
> However, you can do this in a more standard way, should you wish,
> with
> 
> if [[ -n ${VAR+1} ]]; then
>    ...

(Not yet *that* standard, in fact, but Frank has covered that.)

-- 
Peter Stephenson <pws@csr.com>            Software Engineer
Tel: +44 (0)1223 692070                   Cambridge Silicon Radio
Limited Churchill House, Cambridge Business Park, Cowley Road,
Cambridge, CB4 0WZ, UK


Member of the CSR plc group of companies. CSR plc registered in England and Wales, registered number 4187346, registered office Churchill House, Cambridge Business Park, Cowley Road, Cambridge, CB4 0WZ, United Kingdom