I am trying to create a dynamic variable and assign 100 to it
#!/bin/bash
.
.
active_id=$p_val
flag_$active_id=100
But I am getting error in doing so, any help ?
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5possible duplicate of Bash dynamic variable namesrkhayrov– rkhayrov2013-08-02 14:06:27 +00:00Commented Aug 2, 2013 at 14:06
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2 Answers
You can use bash's declare directive and indirection feature like this:
p_val="foo"
active_id=$p_val
declare "flag_$active_id"="100"
TESTING:
> set | grep flag
flag_foo=100
UPDATE:
p_val="foo"
active_id="$p_val"
v="flag_$active_id"
declare "$v"="100"
> echo "$v"
flag_foo
> echo "${!v}"
100
Usage in if condition:
if [ "${!v}" -ne 100 ]; then
echo "yes"
else
echo "no"
fi
# prints no
5 Comments
Shivam Agrawal
thanks anubhava, but i am getting error in this code: if [ flag_$active_id -ne 100 ] then ... else ...
anubhava
@ShivamAgrawal: Check my Update section, I have provided an example of its use in
if then ... else ... fi block.Shivam Agrawal
what is the significance of semicolon here "if [ "${!v}" -ne 100 ];"
anubhava
"${!v}" is called indirection which means the real variable name is contained in $v (flag_foo)
phil294
this does not work for assigning an array. solution is here: stackoverflow.com/a/16487405/3779853
I don't know what this should be good for but you can achieve stuff like this with bash's eval statement.
The following code illustrates that.
#!/bin/bash
p_val="TEST"
active_id=$p_val
eval "flag_$active_id=100"
echo $flag_TEST
eval "echo \$flag_$active_id"
The terminating echo's puts
100
100
on the stdout.
1 Comment
JAR.JAR.beans
Just a friendly word of warning, while this will work, eval is a super dangerous, specially on the shell. so never use in anything that comes from user input. ever.