From: Keith Christian <keith1christian@gmail.com>
To: cygwin@cygwin.com
Subject: Re: Help with C clearenv and setenv
Date: Thu, 31 May 2018 21:53:00 -0000 [thread overview]
Message-ID: <CAFWoy7FyhOF65S_wQ4DEYM=cMn7p0vsTpYJP73UZaQhGCUkXnA@mail.gmail.com> (raw)
In-Reply-To: <CABHT9632LBGQZmRQjyifmd2vWLu24XCP8oJEaMYWu8qHsvpP+A@mail.gmail.com>
You're welcome, Sam.
Keith
On Wed, May 30, 2018 at 8:22 PM, Sam Habiel <sam.habiel@gmail.com> 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@gmail.com>
> 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@gmail.com> 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/)
>> >
>> > --
>> > Problem reports: http://cygwin.com/problems.html
>> > FAQ: http://cygwin.com/faq/
>> > Documentation: http://cygwin.com/docs.html
>> > Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
>> >
>>
>> --
>> Problem reports: http://cygwin.com/problems.html
>> FAQ: http://cygwin.com/faq/
>> Documentation: http://cygwin.com/docs.html
>> Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
>>
>>
>
> --
> Problem reports: http://cygwin.com/problems.html
> FAQ: http://cygwin.com/faq/
> Documentation: http://cygwin.com/docs.html
> Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
>
--
Problem reports: http://cygwin.com/problems.html
FAQ: http://cygwin.com/faq/
Documentation: http://cygwin.com/docs.html
Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
next prev parent reply other threads:[~2018-05-31 14:34 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-30 16:55 Sam Habiel
2018-05-31 3:56 ` Keith Christian
2018-05-31 8:58 ` Sam Habiel
2018-05-31 21:53 ` Keith Christian [this message]
2018-05-31 9:38 ` Marco Atzeri
2018-05-31 13:22 ` Eliot Moss
2018-05-31 17:57 ` Eric Blake
2018-06-04 19:39 ` Ken Brown
2018-06-04 20:22 ` Sam Habiel
2018-06-06 13:02 ` Sam Habiel
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAFWoy7FyhOF65S_wQ4DEYM=cMn7p0vsTpYJP73UZaQhGCUkXnA@mail.gmail.com' \
--to=keith1christian@gmail.com \
--cc=cygwin@cygwin.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).