I've the following bash script:
------- begin --------
#!/usr/bin/env bash
nohup while :; do
if some-cond; then
nohup some-command &>/dev/null &
fi
sleep 5
done &>/dev/null &
------- end --------
It seems that the first “nohup” in the script is
unnecessary/superfluous, i.e., the same effect can be achieved
with or without it - after I exit the terminal, the process still
keeps running.
On Thu, 23 Dec 2021 01:21:45 -0800 (PST)
"hongy...@gmail.com" <hongy...@gmail.com> wrote:
I've the following bash script:
------- begin --------
#!/usr/bin/env bash
nohup while :; do
if some-cond; then
nohup some-command &>/dev/null &
fi
sleep 5
done &>/dev/null &
------- end --------
It seems that the first “nohup” in the script is unnecessary/superfluous, i.e., the same effect can be achievedI don't think that nohup is a shell builtin. So if you were to try your construct with actual commands , BASH would print some error message due
with or without it - after I exit the terminal, the process still
keeps running.
to being unable to parse the code. Perhaps you wouldn't see the error message due to the redirections you make but my guess is that you would.
It would have been best if you had actually posted the code with which
you did your experiments instead of replacing it with a generic version.
A generic version which shows the general rule you think applies would
have been fine but *in addition* to actual running code.
[...]On Thu, 23 Dec 2021 01:21:45 -0800 (PST)
"hongy...@gmail.com" <hongy...@gmail.com> wrote:
[...]It seems that the first “nohup” in the script is
unnecessary/superfluous, i.e., the same effect can be achieved
with or without it - after I exit the terminal, the process still
keeps running.
See the following:
#!/usr/bin/env bash
nohup while :; do
if ! lsof -i :18080 &>/dev/null; then
nohup socat -v -d -d TCP4-LISTEN:18080,fork,reuseaddr PROXY:my.domain.com:10.8.10.100:80,proxyport=6002 &>/dev/null &
fi
sleep 5
done &>/dev/null &
"hongy...@gmail.com" <hongy...@gmail.com> writes:
[...]
[...]On Thu, 23 Dec 2021 01:21:45 -0800 (PST)
"hongy...@gmail.com" <hongy...@gmail.com> wrote:
[...]It seems that the first “nohup” in the script is
unnecessary/superfluous, i.e., the same effect can be achieved
with or without it - after I exit the terminal, the process still
keeps running.
See the following:
#!/usr/bin/env bash
nohup while :; doYes, I see it. What about it? Did you run it? What happened?
if ! lsof -i :18080 &>/dev/null; then
nohup socat -v -d -d TCP4-LISTEN:18080,fork,reuseaddr PROXY:my.domain.com:10.8.10.100:80,proxyport=6002 &>/dev/null &
fi
sleep 5
done &>/dev/null &
In your initial post, you say the first "nohup" is superfluous, that the same effect is achieved with or without it. But when I try to run your most recent script, I get the result I expected:
./tmp.bash: line 3: syntax error near unexpected token `do'
./tmp.bash: line 3: `nohup while :; do'
Either you got the same error message and didn't bother to mention it,
or you didn't get the same error message and something very strange is
going on (perhaps the script you posted doesn't match the script you
ran). Which is it?
I've the following bash script:
------- begin --------
#!/usr/bin/env bash
nohup while :; do
if some-cond; then
nohup some-command &>/dev/null &
fi
sleep 5
done &>/dev/null &
------- end --------
It seems that the first “nohup” in the script is unnecessary/superfluous, i.e., the same effect can be achieved with or without it - after I exit the terminal, the process still keeps running.
Are there any tips for this behavior of the bash shell?
Regards,
HZ
On 23/12/2021 09:21, hongy...@gmail.com wrote:
I've the following bash script:
------- begin --------
#!/usr/bin/env bash
nohup while :; do
if some-cond; then
nohup some-command &>/dev/null &
fi
sleep 5
done &>/dev/null &
------- end --------
It seems that the first “nohup” in the script is unnecessary/superfluous, i.e., the same effect can be achieved with or without it - after I exit the terminal, the process still keeps running.
Are there any tips for this behavior of the bash shell?
Regards,Does it really need to check every 5 seconds?
HZ
Why can't you just cron it every minute?
I've the following bash script:while is a built in, no need for that here
------- begin --------
#!/usr/bin/env bash
nohup while :; do
if some-cond; then
nohup some-command &>/dev/null &
fiWhat happens if 'some-cond' always succeeds and
sleep 5
done &>/dev/null &
------- end --------
Are there any tips for this behavior of the bash shell?
nohup here is a builtin too, there is an external nohup
but you need specify something like /usr/bin/nohup
instead.
On 24.12.2021 14:28, John McCue wrote:
nohup here is a builtin too, there is an external nohup
but you need specify something like /usr/bin/nohup
instead.
That's not true.
Janis
nohup here is a builtin too, there is an external nohup[...]
but you need specify something like /usr/bin/nohup
instead.
On 24.12.2021 21:55, John McCue wrote:
Janis Papanagnou <janis_papanagnou@hotmail.com> wrote:
On 24.12.2021 14:28, John McCue wrote:
nohup here is a builtin too, there is an external nohup
but you need specify something like /usr/bin/nohup
instead.
That's not true.
Interesting, for me it is:
which nohup
nohup: shell built-in command.
Out of curiosity; which shell is that?
But I went into bash and it is not, I was not expecting that.
Good to know.
So it depends upon your shell.
Yes, it's up to the shell whether a command is provided as builtin
or not. I've tried with ksh, which has a builtin command that shows
all the builtins, but you can also use an own test (disabling PATH)
$ bash -c '( PATH= ; nohup sleep 1 )'
bash: nohup: No such file or directory
(or use 'which' or 'whence -a' depending on your system environment
or shell). Also in Ksh (and I think in Bash as well) it's possible
to implement a builtin nohup and dynamically load it as builtin, so
it's also no static property of any shell but depends on the actual
system. It boils down to not making any assumptions about builtins,
unless the standardized ones.
"which" is typically an external command and *not* a builtin, so it has
no way of knowing about builtins for the current shell.
For Bourne-like shells, I find "type" or "type -a" (a builtin) to be
much better than "which".
Janis Papanagnou <janis_papanagnou@hotmail.com> wrote:
On 24.12.2021 14:28, John McCue wrote:
nohup here is a builtin too, there is an external nohup
but you need specify something like /usr/bin/nohup
instead.
That's not true.
Interesting, for me it is:
which nohup
nohup: shell built-in command.
But I went into bash and it is not, I was not expecting that.
Good to know.
So it depends upon your shell.
John McCue <jmccue@fuzzball.mhome.org> writes:
[...]
nohup here is a builtin too, there is an external nohup[...]
but you need specify something like /usr/bin/nohup
instead.
nohup is a builtin in csh and tcsh, not in bash, ksh, or zsh.
If you're using csh, it's definitely worth mentioning that fact.
On 24.12.2021 21:55, John McCue wrote:<snip>
Janis Papanagnou <janis_papanagnou@hotmail.com> wrote:
On 24.12.2021 14:28, John McCue wrote:
Out of curiosity; which shell is that?
Janis
Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:
John McCue <jmccue@fuzzball.mhome.org> writes:
[...]
nohup here is a builtin too, there is an external nohup[...]
but you need specify something like /usr/bin/nohup
instead.
nohup is a builtin in csh and tcsh, not in bash, ksh, or zsh.
If you're using csh, it's definitely worth mentioning that fact.
Only on aix, but on systems that come with tcsh, I use that :)
On 24.12.2021 21:55, John McCue wrote:
Janis Papanagnou <janis_papanagnou@hotmail.com> wrote:
On 24.12.2021 14:28, John McCue wrote:
nohup here is a builtin too, there is an external nohup
but you need specify something like /usr/bin/nohup
instead.
That's not true.
Interesting, for me it is:
which nohup
nohup: shell built-in command.
Out of curiosity; which shell is that?
But I went into bash and it is not, I was not expecting that.
Good to know.
So it depends upon your shell.
Yes, it's up to the shell whether a command is provided as builtin
or not. I've tried with ksh, which has a builtin command that shows
all the builtins, but you can also use an own test (disabling PATH)
$ bash -c '( PATH= ; nohup sleep 1 )'
bash: nohup: No such file or directory
(or use 'which' or 'whence -a' depending on your system environment
or shell). Also in Ksh (and I think in Bash as well) it's possible
to implement a builtin nohup and dynamically load it as builtin, so
it's also no static property of any shell but depends on the actual
system. It boils down to not making any assumptions about builtins,
unless the standardized ones.
Janis
On 25.12.2021 01:27, John McCue wrote:
Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:
John McCue <jmccue@fuzzball.mhome.org> writes:
[...]
nohup here is a builtin too, there is an external nohup[...]
but you need specify something like /usr/bin/nohup
instead.
nohup is a builtin in csh and tcsh, not in bash, ksh, or zsh.
If you're using csh, it's definitely worth mentioning that fact.
Only on aix, but on systems that come with tcsh, I use that :)
The problem is that the OP used a sh based shell - the shell family
used for programming (as opposed to the csh family, deprecated for
that purpose) -, and so it's misleading to inspect ones interactive
csh based shell to test for the buitin status of a command used in
the actually used shell for programming.
I've the following bash script:while is a built in, no need for that here
------- begin --------
#!/usr/bin/env bash
nohup while :; do
if some-cond; then
nohup some-command &>/dev/null &
John McCue <jmc...@fuzzball.mhome.org> writes:
[...]
nohup here is a builtin too, there is an external nohup[...]
but you need specify something like /usr/bin/nohup
instead.
nohup is a builtin in csh and tcsh, not in bash, ksh, or zsh.
If you're using csh, it's definitely worth mentioning that fact.
--
Keith Thompson (The_Other_Keith) Keith.S.T...@gmail.com
Working, but not speaking, for Philips
void Void(void) { Void(); } /* The recursive call of the void */
On Sat, 25 Dec 2021 01:47:33 +0100
Janis Papanagnou <janis_papanagnou@hotmail.com> wrote:
The problem is that the OP used a sh based shell - the shell family
used for programming (as opposed to the csh family, deprecated for
that purpose) -, and so it's misleading to inspect ones interactive
csh based shell to test for the buitin status of a command used in
the actually used shell for programming.
What shell one uses for programming is up to personal taste
so it's
meaningless to say things like "the shell family used for programming" or "deprecated for that purpose" or "the actually used shell for programming".
On Sat, 25 Dec 2021 01:47:33 +0100
Janis Papanagnou <janis_papanagnou@hotmail.com> wrote:
On 25.12.2021 01:27, John McCue wrote:
Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:
John McCue <jmccue@fuzzball.mhome.org> writes:
[...]
nohup here is a builtin too, there is an external nohup[...]
but you need specify something like /usr/bin/nohup
instead.
nohup is a builtin in csh and tcsh, not in bash, ksh, or zsh.
If you're using csh, it's definitely worth mentioning that fact.
Only on aix, but on systems that come with tcsh, I use that :)
The problem is that the OP used a sh based shell - the shell family
used for programming (as opposed to the csh family, deprecated for
that purpose) -, and so it's misleading to inspect ones interactive
csh based shell to test for the buitin status of a command used in
the actually used shell for programming.
[...]
So it quotes code which explicitly mentions BASH .In such a context , it seems to me that the natural interpretation of "nohup here is a builtin too" is that some version of BASH is being referenced. Since John really meant (t)csh , he should have made that explicit.
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