What does colon (':') in bash variable resolution syntax mean?

Question

I need to decode this assignment:

jvm_xmx=${jvm_xmx:-1024}

Yep, seems like a duplicate. But original topic title makes it unsearchable. — user1065145, Jul 08 '15 at 08:56

score 12 · Accepted Answer · answered Jul 08 '15 at 09:01

12

man page for bash:

${parameter:-word}
          Use Default Values.  If parameter is unset or null, the expansion of
          word is substituted.  Otherwise, the value of parameter is substituted.

So if jvm_xmx is already set to something, it is left unchanged.
If it is not already set to something, it is set to 1024.

Example:

$ echo $jvm_xmx

$ jvm_xmx=${jvm_xmx:-1024}
$ echo $jvm_xmx
1024
$ jvm_xmx=2048
$ jvm_xmx=${jvm_xmx:-1024}
$ echo $jvm_xmx
2048
$

answered Jul 08 '15 at 09:01

steve

21,892

Thanks for answer. What does it mean when parameter is @ ? For example: ${@:10} – Atul Dec 05 '19 at 11:06
1

Best to submit a whole new question for that, if the man page doesn't cover it for you. – steve Dec 06 '19 at 09:53

What does colon (':') in bash variable resolution syntax mean?

1 Answers1