Store $(java -version) into a bash variable
Why when I do this: $ var=$(java -version) on my bash terminal, var is always empty? Same thing with $ java -version >> version.txt nothing is sent to the version.txt file.
bash java
asked Dec 12 at 17:18
akuma8
1052
add a comment |
Why when I do this: $ var=$(java -version) on my bash terminal, var is always empty? Same thing with $ java -version >> version.txt nothing is sent to the version.txt file.
bash java
asked Dec 12 at 17:18
akuma8
1052
add a comment |
Why when I do this: $ var=$(java -version) on my bash terminal, var is always empty? Same thing with $ java -version >> version.txt nothing is sent to the version.txt file.
bash java
asked Dec 12 at 17:18
akuma8
1052
Why when I do this: $ var=$(java -version) on my bash terminal, var is always empty? Same thing with $ java -version >> version.txt nothing is sent to the version.txt file.
bash java
bash java
asked Dec 12 at 17:18
akuma8
1052
asked Dec 12 at 17:18
akuma8
1052
asked Dec 12 at 17:18
akuma8
1052
asked Dec 12 at 17:18
akuma8
1052
asked Dec 12 at 17:18
akuma8
1052
1052
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
The command usually send such information to STDERR, not STDOUT. So in your case you should use commands like:
java -version >>version.txt 2>&1
and
var=$((java -version) 2>&1)
edited Dec 12 at 22:30
Kamil Maciorowski
23.7k155074
answered Dec 12 at 17:56
Romeo Ninov
1,6641914
1
I don't know why you have put the inner brackets roundjava -version: they are unnecessary and invoke a further subshell needlessly.
– AFH
Dec 12 at 18:30
add a comment |
As Romeo has pointed, java -version writes in stderr, not in stdout, so you should use:
var=$(java -version 2>&1)
If you want to get the version only and not all the output of the java -version command, more convinient for scripting for example, you can use something like:
var=$(java -version 2>&1 | awk -F '"' 'NR==1 {print $2}')
Explanation
java -versionprints java version message into stderr
2>&1redirects stderr to stdout
|takes lefthand command output and use it as input for righthand command
awk -F '"' 'NR==1 {print $2}'is a bit more complicated, but basically it divides the input it receives into parts, allowing you to operate with each part separately (the most knowledgeable probably will throw me to the lions, it is a very bad summary of what is and what awk does).
- The character that
awktakes for the division is specified by the-Foption, in this case it is divided by the character"
- The last part specifies that only the second element (
{print $2}) from the first line (NR==1) of the resulting division must be printed.
- The character that
This will output something like 1.8.0_191.
edited Dec 12 at 22:34
Kamil Maciorowski
23.7k155074
answered Dec 12 at 22:11
Álvaro Orduna León
312
1
Thanks for the explanation. I am wondering why Java uses STDERR instead of STDOUT and how do you know this?
– akuma8
Dec 13 at 8:53
add a comment |
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2 Answers
2
active
oldest
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2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
The command usually send such information to STDERR, not STDOUT. So in your case you should use commands like:
java -version >>version.txt 2>&1
and
var=$((java -version) 2>&1)
edited Dec 12 at 22:30
Kamil Maciorowski
23.7k155074
answered Dec 12 at 17:56
Romeo Ninov
1,6641914
1
I don't know why you have put the inner brackets roundjava -version: they are unnecessary and invoke a further subshell needlessly.
– AFH
Dec 12 at 18:30
add a comment |
The command usually send such information to STDERR, not STDOUT. So in your case you should use commands like:
java -version >>version.txt 2>&1
and
var=$((java -version) 2>&1)
edited Dec 12 at 22:30
Kamil Maciorowski
23.7k155074
answered Dec 12 at 17:56
Romeo Ninov
1,6641914
1
I don't know why you have put the inner brackets roundjava -version: they are unnecessary and invoke a further subshell needlessly.
– AFH
Dec 12 at 18:30
add a comment |
The command usually send such information to STDERR, not STDOUT. So in your case you should use commands like:
java -version >>version.txt 2>&1
and
var=$((java -version) 2>&1)
edited Dec 12 at 22:30
Kamil Maciorowski
23.7k155074
answered Dec 12 at 17:56
Romeo Ninov
1,6641914
The command usually send such information to STDERR, not STDOUT. So in your case you should use commands like:
java -version >>version.txt 2>&1
and
var=$((java -version) 2>&1)
edited Dec 12 at 22:30
Kamil Maciorowski
23.7k155074
answered Dec 12 at 17:56
Romeo Ninov
1,6641914
edited Dec 12 at 22:30
Kamil Maciorowski
23.7k155074
edited Dec 12 at 22:30
Kamil Maciorowski
23.7k155074
edited Dec 12 at 22:30
Kamil Maciorowski
23.7k155074
23.7k155074
answered Dec 12 at 17:56
Romeo Ninov
1,6641914
answered Dec 12 at 17:56
Romeo Ninov
1,6641914
answered Dec 12 at 17:56
Romeo Ninov
1,6641914
1,6641914
1
I don't know why you have put the inner brackets roundjava -version: they are unnecessary and invoke a further subshell needlessly.
– AFH
Dec 12 at 18:30
add a comment |
1
I don't know why you have put the inner brackets roundjava -version: they are unnecessary and invoke a further subshell needlessly.
– AFH
Dec 12 at 18:30
1
1
I don't know why you have put the inner brackets round
java -version: they are unnecessary and invoke a further subshell needlessly.– AFH
Dec 12 at 18:30
I don't know why you have put the inner brackets round
java -version: they are unnecessary and invoke a further subshell needlessly.– AFH
Dec 12 at 18:30
add a comment |
As Romeo has pointed, java -version writes in stderr, not in stdout, so you should use:
var=$(java -version 2>&1)
If you want to get the version only and not all the output of the java -version command, more convinient for scripting for example, you can use something like:
var=$(java -version 2>&1 | awk -F '"' 'NR==1 {print $2}')
Explanation
java -versionprints java version message into stderr
2>&1redirects stderr to stdout
|takes lefthand command output and use it as input for righthand command
awk -F '"' 'NR==1 {print $2}'is a bit more complicated, but basically it divides the input it receives into parts, allowing you to operate with each part separately (the most knowledgeable probably will throw me to the lions, it is a very bad summary of what is and what awk does).
- The character that
awktakes for the division is specified by the-Foption, in this case it is divided by the character"
- The last part specifies that only the second element (
{print $2}) from the first line (NR==1) of the resulting division must be printed.
- The character that
This will output something like 1.8.0_191.
edited Dec 12 at 22:34
Kamil Maciorowski
23.7k155074
answered Dec 12 at 22:11
Álvaro Orduna León
312
1
Thanks for the explanation. I am wondering why Java uses STDERR instead of STDOUT and how do you know this?
– akuma8
Dec 13 at 8:53
add a comment |
As Romeo has pointed, java -version writes in stderr, not in stdout, so you should use:
var=$(java -version 2>&1)
If you want to get the version only and not all the output of the java -version command, more convinient for scripting for example, you can use something like:
var=$(java -version 2>&1 | awk -F '"' 'NR==1 {print $2}')
Explanation
java -versionprints java version message into stderr
2>&1redirects stderr to stdout
|takes lefthand command output and use it as input for righthand command
awk -F '"' 'NR==1 {print $2}'is a bit more complicated, but basically it divides the input it receives into parts, allowing you to operate with each part separately (the most knowledgeable probably will throw me to the lions, it is a very bad summary of what is and what awk does).
- The character that
awktakes for the division is specified by the-Foption, in this case it is divided by the character"
- The last part specifies that only the second element (
{print $2}) from the first line (NR==1) of the resulting division must be printed.
- The character that
This will output something like 1.8.0_191.
edited Dec 12 at 22:34
Kamil Maciorowski
23.7k155074
answered Dec 12 at 22:11
Álvaro Orduna León
312
1
Thanks for the explanation. I am wondering why Java uses STDERR instead of STDOUT and how do you know this?
– akuma8
Dec 13 at 8:53
add a comment |
As Romeo has pointed, java -version writes in stderr, not in stdout, so you should use:
var=$(java -version 2>&1)
If you want to get the version only and not all the output of the java -version command, more convinient for scripting for example, you can use something like:
var=$(java -version 2>&1 | awk -F '"' 'NR==1 {print $2}')
Explanation
java -versionprints java version message into stderr
2>&1redirects stderr to stdout
|takes lefthand command output and use it as input for righthand command
awk -F '"' 'NR==1 {print $2}'is a bit more complicated, but basically it divides the input it receives into parts, allowing you to operate with each part separately (the most knowledgeable probably will throw me to the lions, it is a very bad summary of what is and what awk does).
- The character that
awktakes for the division is specified by the-Foption, in this case it is divided by the character"
- The last part specifies that only the second element (
{print $2}) from the first line (NR==1) of the resulting division must be printed.
- The character that
This will output something like 1.8.0_191.
edited Dec 12 at 22:34
Kamil Maciorowski
23.7k155074
answered Dec 12 at 22:11
Álvaro Orduna León
312
As Romeo has pointed, java -version writes in stderr, not in stdout, so you should use:
var=$(java -version 2>&1)
If you want to get the version only and not all the output of the java -version command, more convinient for scripting for example, you can use something like:
var=$(java -version 2>&1 | awk -F '"' 'NR==1 {print $2}')
Explanation
java -versionprints java version message into stderr
2>&1redirects stderr to stdout
|takes lefthand command output and use it as input for righthand command
awk -F '"' 'NR==1 {print $2}'is a bit more complicated, but basically it divides the input it receives into parts, allowing you to operate with each part separately (the most knowledgeable probably will throw me to the lions, it is a very bad summary of what is and what awk does).
- The character that
awktakes for the division is specified by the-Foption, in this case it is divided by the character"
- The last part specifies that only the second element (
{print $2}) from the first line (NR==1) of the resulting division must be printed.
- The character that
This will output something like 1.8.0_191.
edited Dec 12 at 22:34
Kamil Maciorowski
23.7k155074
answered Dec 12 at 22:11
Álvaro Orduna León
312
edited Dec 12 at 22:34
Kamil Maciorowski
23.7k155074
edited Dec 12 at 22:34
Kamil Maciorowski
23.7k155074
edited Dec 12 at 22:34
Kamil Maciorowski
23.7k155074
23.7k155074
answered Dec 12 at 22:11
Álvaro Orduna León
312
answered Dec 12 at 22:11
Álvaro Orduna León
312
answered Dec 12 at 22:11
Álvaro Orduna León
312
312
1
Thanks for the explanation. I am wondering why Java uses STDERR instead of STDOUT and how do you know this?
– akuma8
Dec 13 at 8:53
add a comment |
1
Thanks for the explanation. I am wondering why Java uses STDERR instead of STDOUT and how do you know this?
– akuma8
Dec 13 at 8:53
1
1
Thanks for the explanation. I am wondering why Java uses STDERR instead of STDOUT and how do you know this?
– akuma8
Dec 13 at 8:53
Thanks for the explanation. I am wondering why Java uses STDERR instead of STDOUT and how do you know this?
– akuma8
Dec 13 at 8:53
add a comment |
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