I have a bash variable: agent1.ip with 192.168.100.137 as its value. When I refer to it in echo like this:
echo $agent1.ip
the result is:
.ip
How can I access the value?
UPDATE: my variables are:
6 Answers
Bash itself doesn't understand variable names with dots in them, but that doesn't mean you can't have such a variable in your environment. Here's an example of how to set it and get it all in one:
env 'agent1.ip=192.168.100.137' bash -c 'env | grep ^agent1\\.ip= | cut -d= -f2-'
3 Comments
Dettorer
Then you can assign that value to a valid bash variable name.
drizzt
The grep regex is wrong, please quote the \ or it will also accept agent1_ip or agent1-ip, etc
John Zwinck
@drizzt: you're right, I added another `` to properly escape the pattern.
Since bash.ip is not a valid identifier in bash, the environment string bash.ip=192.168.100.37 is not used to create a shell variable on shell startup.
I would use awk, a standard tool, to extract the value from the environment.
bash_ip=$(awk 'BEGIN {print ENVIRON["bash.ip"]}')
Comments
The cleanest solution is:
echo path.data | awk '{print ENVIRON[$1]}'
2 Comments
Nate Anderson
Both answers use the awk's
ENVIRON variable, more here , here and here and here. I guess it's not a duplicate of the other answer in that: a) this answer is "shorter" and b) does something different (echos, vs assigns)Is your code nested, and using functions or scripts that use ksh?
Dotted variable names are an advanced feature in ksh93. A simple case is
$ a=1
$ a.b=123
$ echo ${a.b}
123
$ echo $a
1
If you first attempt to assign to a.b, you'll get
-ksh: a.b=123: no parent
IHTH
Comments
Try this:
export myval=`env | grep agent1.port | awk -F'=' '{print $2}'`;echo $myval
1 Comment
John Zwinck
Note that
. in grep means "any character," so this will behave badly if there is e.g. agent1Sport. Likewise flagent1.port or blagent1Sportier. See my answer for a more exact expression.For accessing the environment variable in a readable way, I'd make a shell function of it:
getenv() {
awk 'BEGIN {print ENVIRON[ARGV[1]]}' "$1";
}
You can then use it as
$ getenv agent1.ip
192.168.100.137
$ myvar=$(getenv agent1.ip)
$ echo "$myvar"
192.168.100.137
Differences with the accepted answer are:
- robustness: supports also newlines in the variable value (
grepandcutwork on lines) - efficiency: only one fork (
awk) instead of 3 (env,grep,cut) in a pipeline (which also has to set up i/o buffers)
There is also another question about Exporting a variable with dot (.) in it.
Short answer: you can't, but you needn't, except for calling another executable. In that case use env.
.in the variable name in the first place?bash.ip=192.168.100.137is a perfectly valid string to include in the environment. It's just not a string whichbashcan automatically turn into a variable.