[avar]

:<whatever> means "read it from the <whatever>" file. See the last part of the relevant glibc documentation: https://www.gnu.org/savannah-checkouts/gnu/libc/manual/html_...

However the reason it works without : is that the implementation is being lazy and just ignores the : delimiter and falls back to parsing out a filename either way:

https://sourceware.org/git/?p=glibc.git;a=blob;f=time/tzset....

[rootbear]

You beat me to it. I was answering my own question when one of my users came in with a problem. Stupid users...