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Re: Help with C clearenv and setenv




You're welcome, Sam.

Keith

On Wed, May 30, 2018 at 8:22 PM, Sam Habiel <sam.habiel@xxxxxxxxx> wrote:
> Thank you Keith for you reply; but I am actually looking for the C APIs to
> manipulate the environment; esp. to clear it.
>
> On Wed, May 30, 2018 at 6:05 PM, Keith Christian <keith1christian@xxxxxxxxx>
> wrote:
>
>> Sam,
>>
>> Here is a short demonstration of how to detect unset (possibly null,
>> too?) variables in BASH.  Not sure if this is exactly what you are
>> looking for but presented for info.
>>
>> set -x;A_VAR="${RANDOM}";echo "1. ${A_VAR}";echo "2.
>> ${A_VAR:?IS_NOT_SET}";unset A_VAR;set +x
>> + set -x
>> + A_VAR=28641
>> + echo '1. 28641'
>> 1. 28641
>> + echo '2. 28641'
>> 2. 28641
>> + unset A_VAR
>> -bash: A_VAR: IS_NOT_SET
>>
>>
>> Documentation for is in the BASH texinfo docs, read it in a Cygwin
>> terminal by typing "info bash" and go to this section:
>>
>>
>> 3.5.3 Shell Parameter Expansion
>> -------------------------------
>> (( lines deleted ))  (( lines deleted ))  (( lines deleted ))
>> '${PARAMETER:-WORD}'
>>      If PARAMETER is unset or null, the expansion of WORD is
>>      substituted.  Otherwise, the value of PARAMETER is substituted.
>>
>> '${PARAMETER:=WORD}'
>>      If PARAMETER is unset or null, the expansion of WORD is assigned to
>>      PARAMETER.  The value of PARAMETER is then substituted.  Positional
>>      parameters and special parameters may not be assigned to in this
>>      way.
>>
>> '${PARAMETER:?WORD}'
>>      If PARAMETER is null or unset, the expansion of WORD (or a message
>>      to that effect if WORD is not present) is written to the standard
>>      error and the shell, if it is not interactive, exits.  Otherwise,
>>      the value of PARAMETER is substituted.
>>
>> '${PARAMETER:+WORD}'
>>      If PARAMETER is null or unset, nothing is substituted, otherwise
>>      the expansion of WORD is substituted.
>> (( lines deleted ))  (( lines deleted ))  (( lines deleted ))
>>
>> Keith
>>
>> On Wed, May 30, 2018 at 8:48 AM, Sam Habiel <sam.habiel@xxxxxxxxx> wrote:
>> > I have code for a database I am porting to Cygwin.
>> >
>> > Part of that code is a clearenv() then a couple of setenvs. There is
>> > an ifdef for Cygwin, as it doesn't implement clearenv. It just sets
>> > environ = NULL. Well--that really breaks setenv! It returns a "Bad
>> > Poniter" error (-1).
>> >
>> > What is the correct way to clear environment variables in Cygwin?
>> >
>> > --Sam
>> > (About me: http://smh101.com/)
>> >
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