Shell program to just open a character driver and wait
What inspired this question is that I am testing the functionality of watchdog device and I was thinking if there is a shell inbuilt command to just open the device and do nothing/wait until terminated?
Echo/touch seem to just open and close the device immediately after performing the operation. Cat does not seem to work.
I am using a C application to do the same but was wondering if shell script has some provision for it
linux bash shell-script
asked Dec 10 at 13:14
yashC
557
add a comment |
What inspired this question is that I am testing the functionality of watchdog device and I was thinking if there is a shell inbuilt command to just open the device and do nothing/wait until terminated?
Echo/touch seem to just open and close the device immediately after performing the operation. Cat does not seem to work.
I am using a C application to do the same but was wondering if shell script has some provision for it
linux bash shell-script
asked Dec 10 at 13:14
yashC
557
add a comment |
What inspired this question is that I am testing the functionality of watchdog device and I was thinking if there is a shell inbuilt command to just open the device and do nothing/wait until terminated?
Echo/touch seem to just open and close the device immediately after performing the operation. Cat does not seem to work.
I am using a C application to do the same but was wondering if shell script has some provision for it
linux bash shell-script
asked Dec 10 at 13:14
yashC
557
What inspired this question is that I am testing the functionality of watchdog device and I was thinking if there is a shell inbuilt command to just open the device and do nothing/wait until terminated?
Echo/touch seem to just open and close the device immediately after performing the operation. Cat does not seem to work.
I am using a C application to do the same but was wondering if shell script has some provision for it
linux bash shell-script
linux bash shell-script
asked Dec 10 at 13:14
yashC
557
asked Dec 10 at 13:14
yashC
557
asked Dec 10 at 13:14
yashC
557
asked Dec 10 at 13:14
yashC
557
asked Dec 10 at 13:14
yashC
557
557
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
In Bourne-like shells,
exec 3< "$device"
Opens the device on file descriptor 3 of the shell.
That would be more or less equivalent to C's:
fd = open(device, O_RDONLY);
if (fd < 0) handler_error(...);
if (fd != 3) { dup2(fd, 3); close(fd); }
(ksh93 also does a fcntl(3, F_SETFD, FD_CLOEXEC) on that fd).
To close it: exec 3<&-
In zsh, ksh93 and bash, the equivalent of fd = open(device, O_RDONLY) could also be written as:
exec {fd}< "$device"
Where the file descriptor would be the first free one above 9 and stored in $fd.
To close it: exec {fd}<&-
Replace < with > for O_WRONLY|O_CREAT|O_TRUNC, and with <> for O_RDWR|O_CREAT and >> for O_WRONLY|O_CREAT|O_APPEND.
zsh also has a sysopen builtin (in the zsh/system module) where you can specify the flags exactly.
Note that in POSIX compliant shells, exec being a special builtin, if the file can't be opened, it's a fatal error when non-interactive (it exits the script). You can disabled that by using the command command.
if command exec 3< "$device"; then
do-what-you-need-to-do
else
handle-the-error-yourself
fi
answered Dec 10 at 13:18
Stéphane Chazelas
298k54563910
add a comment |
while sleep 3600; do :; done >/dev/your_watchdog
I gather (from the echo and touch working and the cat failing) that the device should be open in write only mode.
answered Dec 10 at 14:45
pizdelect
31216
sleep 1e99 >/dev/your_watchdogwould also work, assuming you're not planning on being after 10 to the 91 years or so...
– Digital Trauma
Dec 10 at 20:38
sleep: invalid number '1e99';-)
– pizdelect
Dec 11 at 2:03
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
In Bourne-like shells,
exec 3< "$device"
Opens the device on file descriptor 3 of the shell.
That would be more or less equivalent to C's:
fd = open(device, O_RDONLY);
if (fd < 0) handler_error(...);
if (fd != 3) { dup2(fd, 3); close(fd); }
(ksh93 also does a fcntl(3, F_SETFD, FD_CLOEXEC) on that fd).
To close it: exec 3<&-
In zsh, ksh93 and bash, the equivalent of fd = open(device, O_RDONLY) could also be written as:
exec {fd}< "$device"
Where the file descriptor would be the first free one above 9 and stored in $fd.
To close it: exec {fd}<&-
Replace < with > for O_WRONLY|O_CREAT|O_TRUNC, and with <> for O_RDWR|O_CREAT and >> for O_WRONLY|O_CREAT|O_APPEND.
zsh also has a sysopen builtin (in the zsh/system module) where you can specify the flags exactly.
Note that in POSIX compliant shells, exec being a special builtin, if the file can't be opened, it's a fatal error when non-interactive (it exits the script). You can disabled that by using the command command.
if command exec 3< "$device"; then
do-what-you-need-to-do
else
handle-the-error-yourself
fi
answered Dec 10 at 13:18
Stéphane Chazelas
298k54563910
add a comment |
In Bourne-like shells,
exec 3< "$device"
Opens the device on file descriptor 3 of the shell.
That would be more or less equivalent to C's:
fd = open(device, O_RDONLY);
if (fd < 0) handler_error(...);
if (fd != 3) { dup2(fd, 3); close(fd); }
(ksh93 also does a fcntl(3, F_SETFD, FD_CLOEXEC) on that fd).
To close it: exec 3<&-
In zsh, ksh93 and bash, the equivalent of fd = open(device, O_RDONLY) could also be written as:
exec {fd}< "$device"
Where the file descriptor would be the first free one above 9 and stored in $fd.
To close it: exec {fd}<&-
Replace < with > for O_WRONLY|O_CREAT|O_TRUNC, and with <> for O_RDWR|O_CREAT and >> for O_WRONLY|O_CREAT|O_APPEND.
zsh also has a sysopen builtin (in the zsh/system module) where you can specify the flags exactly.
Note that in POSIX compliant shells, exec being a special builtin, if the file can't be opened, it's a fatal error when non-interactive (it exits the script). You can disabled that by using the command command.
if command exec 3< "$device"; then
do-what-you-need-to-do
else
handle-the-error-yourself
fi
answered Dec 10 at 13:18
Stéphane Chazelas
298k54563910
add a comment |
In Bourne-like shells,
exec 3< "$device"
Opens the device on file descriptor 3 of the shell.
That would be more or less equivalent to C's:
fd = open(device, O_RDONLY);
if (fd < 0) handler_error(...);
if (fd != 3) { dup2(fd, 3); close(fd); }
(ksh93 also does a fcntl(3, F_SETFD, FD_CLOEXEC) on that fd).
To close it: exec 3<&-
In zsh, ksh93 and bash, the equivalent of fd = open(device, O_RDONLY) could also be written as:
exec {fd}< "$device"
Where the file descriptor would be the first free one above 9 and stored in $fd.
To close it: exec {fd}<&-
Replace < with > for O_WRONLY|O_CREAT|O_TRUNC, and with <> for O_RDWR|O_CREAT and >> for O_WRONLY|O_CREAT|O_APPEND.
zsh also has a sysopen builtin (in the zsh/system module) where you can specify the flags exactly.
Note that in POSIX compliant shells, exec being a special builtin, if the file can't be opened, it's a fatal error when non-interactive (it exits the script). You can disabled that by using the command command.
if command exec 3< "$device"; then
do-what-you-need-to-do
else
handle-the-error-yourself
fi
answered Dec 10 at 13:18
Stéphane Chazelas
298k54563910
In Bourne-like shells,
exec 3< "$device"
Opens the device on file descriptor 3 of the shell.
That would be more or less equivalent to C's:
fd = open(device, O_RDONLY);
if (fd < 0) handler_error(...);
if (fd != 3) { dup2(fd, 3); close(fd); }
(ksh93 also does a fcntl(3, F_SETFD, FD_CLOEXEC) on that fd).
To close it: exec 3<&-
In zsh, ksh93 and bash, the equivalent of fd = open(device, O_RDONLY) could also be written as:
exec {fd}< "$device"
Where the file descriptor would be the first free one above 9 and stored in $fd.
To close it: exec {fd}<&-
Replace < with > for O_WRONLY|O_CREAT|O_TRUNC, and with <> for O_RDWR|O_CREAT and >> for O_WRONLY|O_CREAT|O_APPEND.
zsh also has a sysopen builtin (in the zsh/system module) where you can specify the flags exactly.
Note that in POSIX compliant shells, exec being a special builtin, if the file can't be opened, it's a fatal error when non-interactive (it exits the script). You can disabled that by using the command command.
if command exec 3< "$device"; then
do-what-you-need-to-do
else
handle-the-error-yourself
fi
answered Dec 10 at 13:18
Stéphane Chazelas
298k54563910
edited Dec 10 at 14:08
answered Dec 10 at 13:18
Stéphane Chazelas
298k54563910
answered Dec 10 at 13:18
Stéphane Chazelas
298k54563910
answered Dec 10 at 13:18
Stéphane Chazelas
298k54563910
298k54563910
add a comment |
add a comment |
while sleep 3600; do :; done >/dev/your_watchdog
I gather (from the echo and touch working and the cat failing) that the device should be open in write only mode.
answered Dec 10 at 14:45
pizdelect
31216
sleep 1e99 >/dev/your_watchdogwould also work, assuming you're not planning on being after 10 to the 91 years or so...
– Digital Trauma
Dec 10 at 20:38
sleep: invalid number '1e99';-)
– pizdelect
Dec 11 at 2:03
add a comment |
while sleep 3600; do :; done >/dev/your_watchdog
I gather (from the echo and touch working and the cat failing) that the device should be open in write only mode.
answered Dec 10 at 14:45
pizdelect
31216
sleep 1e99 >/dev/your_watchdogwould also work, assuming you're not planning on being after 10 to the 91 years or so...
– Digital Trauma
Dec 10 at 20:38
sleep: invalid number '1e99';-)
– pizdelect
Dec 11 at 2:03
add a comment |
while sleep 3600; do :; done >/dev/your_watchdog
I gather (from the echo and touch working and the cat failing) that the device should be open in write only mode.
answered Dec 10 at 14:45
pizdelect
31216
while sleep 3600; do :; done >/dev/your_watchdog
I gather (from the echo and touch working and the cat failing) that the device should be open in write only mode.
answered Dec 10 at 14:45
pizdelect
31216
answered Dec 10 at 14:45
pizdelect
31216
answered Dec 10 at 14:45
pizdelect
31216
answered Dec 10 at 14:45
pizdelect
31216
31216
sleep 1e99 >/dev/your_watchdogwould also work, assuming you're not planning on being after 10 to the 91 years or so...
– Digital Trauma
Dec 10 at 20:38
sleep: invalid number '1e99';-)
– pizdelect
Dec 11 at 2:03
add a comment |
sleep 1e99 >/dev/your_watchdogwould also work, assuming you're not planning on being after 10 to the 91 years or so...
– Digital Trauma
Dec 10 at 20:38
sleep: invalid number '1e99';-)
– pizdelect
Dec 11 at 2:03
sleep 1e99 >/dev/your_watchdog would also work, assuming you're not planning on being after 10 to the 91 years or so...– Digital Trauma
Dec 10 at 20:38
sleep 1e99 >/dev/your_watchdog would also work, assuming you're not planning on being after 10 to the 91 years or so...– Digital Trauma
Dec 10 at 20:38
sleep: invalid number '1e99' ;-)– pizdelect
Dec 11 at 2:03
sleep: invalid number '1e99' ;-)– pizdelect
Dec 11 at 2:03
add a comment |
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