Saving a < /dev/null result from remote host to local machine in text file
I have the following code, which retrieves data from a remote host and display on local machine display.
if [ $(nc -z 192.168.80.180 22; echo $?) -eq 0 ]; then
ssh root@$192.168.80.180 'df -h; free -m' < /dev/null
echo /dev/null | cat - $var.txt
fi
How can I capture the result and save to a file, I tried echo but it didn't work.
Thank You
bash scripting
asked Nov 27 '18 at 20:58
Huud RychHuud Rych
65
add a comment |
I have the following code, which retrieves data from a remote host and display on local machine display.
if [ $(nc -z 192.168.80.180 22; echo $?) -eq 0 ]; then
ssh root@$192.168.80.180 'df -h; free -m' < /dev/null
echo /dev/null | cat - $var.txt
fi
How can I capture the result and save to a file, I tried echo but it didn't work.
Thank You
bash scripting
asked Nov 27 '18 at 20:58
Huud RychHuud Rych
65
add a comment |
I have the following code, which retrieves data from a remote host and display on local machine display.
if [ $(nc -z 192.168.80.180 22; echo $?) -eq 0 ]; then
ssh root@$192.168.80.180 'df -h; free -m' < /dev/null
echo /dev/null | cat - $var.txt
fi
How can I capture the result and save to a file, I tried echo but it didn't work.
Thank You
bash scripting
asked Nov 27 '18 at 20:58
Huud RychHuud Rych
65
I have the following code, which retrieves data from a remote host and display on local machine display.
if [ $(nc -z 192.168.80.180 22; echo $?) -eq 0 ]; then
ssh root@$192.168.80.180 'df -h; free -m' < /dev/null
echo /dev/null | cat - $var.txt
fi
How can I capture the result and save to a file, I tried echo but it didn't work.
Thank You
bash scripting
bash scripting
asked Nov 27 '18 at 20:58
Huud RychHuud Rych
65
asked Nov 27 '18 at 20:58
Huud RychHuud Rych
65
asked Nov 27 '18 at 20:58
Huud RychHuud Rych
65
asked Nov 27 '18 at 20:58
Huud RychHuud Rych
65
asked Nov 27 '18 at 20:58
Huud RychHuud Rych
65
65
add a comment |
add a comment |
1 Answer
1
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oldest
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< /dev/null
Binds the process standard output with /dev/null file.
Saving a < /dev/null result ...
/dev/null is a file and does not produce a result.
ssh root@$192.168.80.180 'df -h; free -m' < /dev/null
Runs ssh command with specified parameters and binds it's standard input with /dev/null.
/dev/null is a magic file. It always has size equal to zero. You can write anything to it. It's size still will be zero. You can't read anything from it. Cause it's size is always zero. Expression < /dev/zero is used to "close" a commands standard input.
For saving a process output it produces on standard output you can use command substitution:
var=$(ssh root@$192.168.80.180 'df -h; free -m' < /dev/null)
or you can save the standard output of a process by binding it with a file:
ssh root@$192.168.80.180 'df -h; free -m' < /dev/null > result.txt
You can read more about bash redirections.
The line
if [ $(nc -z 192.168.80.180 22; echo $?) -eq 0 ]; then
is just strange. Just:
if nc -z 192.168.80.180 22; then
The if expression is true if the command returns zero status. Comparing commands return status with zero [ $(command; echo $?) -eq 0 ] is just strange.
More about if.
Also always quote any expansions (unless you know you don't have to). So quote command substitution [ "$(nc -z ...; echo $?)" -eq 0 ].
answered Nov 27 '18 at 21:06
Kamil CukKamil Cuk
11.9k1529
add a comment |
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1 Answer
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active
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1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
< /dev/null
Binds the process standard output with /dev/null file.
Saving a < /dev/null result ...
/dev/null is a file and does not produce a result.
ssh root@$192.168.80.180 'df -h; free -m' < /dev/null
Runs ssh command with specified parameters and binds it's standard input with /dev/null.
/dev/null is a magic file. It always has size equal to zero. You can write anything to it. It's size still will be zero. You can't read anything from it. Cause it's size is always zero. Expression < /dev/zero is used to "close" a commands standard input.
For saving a process output it produces on standard output you can use command substitution:
var=$(ssh root@$192.168.80.180 'df -h; free -m' < /dev/null)
or you can save the standard output of a process by binding it with a file:
ssh root@$192.168.80.180 'df -h; free -m' < /dev/null > result.txt
You can read more about bash redirections.
The line
if [ $(nc -z 192.168.80.180 22; echo $?) -eq 0 ]; then
is just strange. Just:
if nc -z 192.168.80.180 22; then
The if expression is true if the command returns zero status. Comparing commands return status with zero [ $(command; echo $?) -eq 0 ] is just strange.
More about if.
Also always quote any expansions (unless you know you don't have to). So quote command substitution [ "$(nc -z ...; echo $?)" -eq 0 ].
answered Nov 27 '18 at 21:06
Kamil CukKamil Cuk
11.9k1529
add a comment |
< /dev/null
Binds the process standard output with /dev/null file.
Saving a < /dev/null result ...
/dev/null is a file and does not produce a result.
ssh root@$192.168.80.180 'df -h; free -m' < /dev/null
Runs ssh command with specified parameters and binds it's standard input with /dev/null.
/dev/null is a magic file. It always has size equal to zero. You can write anything to it. It's size still will be zero. You can't read anything from it. Cause it's size is always zero. Expression < /dev/zero is used to "close" a commands standard input.
For saving a process output it produces on standard output you can use command substitution:
var=$(ssh root@$192.168.80.180 'df -h; free -m' < /dev/null)
or you can save the standard output of a process by binding it with a file:
ssh root@$192.168.80.180 'df -h; free -m' < /dev/null > result.txt
You can read more about bash redirections.
The line
if [ $(nc -z 192.168.80.180 22; echo $?) -eq 0 ]; then
is just strange. Just:
if nc -z 192.168.80.180 22; then
The if expression is true if the command returns zero status. Comparing commands return status with zero [ $(command; echo $?) -eq 0 ] is just strange.
More about if.
Also always quote any expansions (unless you know you don't have to). So quote command substitution [ "$(nc -z ...; echo $?)" -eq 0 ].
answered Nov 27 '18 at 21:06
Kamil CukKamil Cuk
11.9k1529
add a comment |
< /dev/null
Binds the process standard output with /dev/null file.
Saving a < /dev/null result ...
/dev/null is a file and does not produce a result.
ssh root@$192.168.80.180 'df -h; free -m' < /dev/null
Runs ssh command with specified parameters and binds it's standard input with /dev/null.
/dev/null is a magic file. It always has size equal to zero. You can write anything to it. It's size still will be zero. You can't read anything from it. Cause it's size is always zero. Expression < /dev/zero is used to "close" a commands standard input.
For saving a process output it produces on standard output you can use command substitution:
var=$(ssh root@$192.168.80.180 'df -h; free -m' < /dev/null)
or you can save the standard output of a process by binding it with a file:
ssh root@$192.168.80.180 'df -h; free -m' < /dev/null > result.txt
You can read more about bash redirections.
The line
if [ $(nc -z 192.168.80.180 22; echo $?) -eq 0 ]; then
is just strange. Just:
if nc -z 192.168.80.180 22; then
The if expression is true if the command returns zero status. Comparing commands return status with zero [ $(command; echo $?) -eq 0 ] is just strange.
More about if.
Also always quote any expansions (unless you know you don't have to). So quote command substitution [ "$(nc -z ...; echo $?)" -eq 0 ].
answered Nov 27 '18 at 21:06
Kamil CukKamil Cuk
11.9k1529
< /dev/null
Binds the process standard output with /dev/null file.
Saving a < /dev/null result ...
/dev/null is a file and does not produce a result.
ssh root@$192.168.80.180 'df -h; free -m' < /dev/null
Runs ssh command with specified parameters and binds it's standard input with /dev/null.
/dev/null is a magic file. It always has size equal to zero. You can write anything to it. It's size still will be zero. You can't read anything from it. Cause it's size is always zero. Expression < /dev/zero is used to "close" a commands standard input.
For saving a process output it produces on standard output you can use command substitution:
var=$(ssh root@$192.168.80.180 'df -h; free -m' < /dev/null)
or you can save the standard output of a process by binding it with a file:
ssh root@$192.168.80.180 'df -h; free -m' < /dev/null > result.txt
You can read more about bash redirections.
The line
if [ $(nc -z 192.168.80.180 22; echo $?) -eq 0 ]; then
is just strange. Just:
if nc -z 192.168.80.180 22; then
The if expression is true if the command returns zero status. Comparing commands return status with zero [ $(command; echo $?) -eq 0 ] is just strange.
More about if.
Also always quote any expansions (unless you know you don't have to). So quote command substitution [ "$(nc -z ...; echo $?)" -eq 0 ].
answered Nov 27 '18 at 21:06
Kamil CukKamil Cuk
11.9k1529
answered Nov 27 '18 at 21:06
Kamil CukKamil Cuk
11.9k1529
answered Nov 27 '18 at 21:06
Kamil CukKamil Cuk
11.9k1529
answered Nov 27 '18 at 21:06
Kamil CukKamil Cuk
11.9k1529
11.9k1529
add a comment |
add a comment |
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