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Some Special Array Variables Only Kind Of Initialized


From: John R. Graham
Subject: Some Special Array Variables Only Kind Of Initialized
Date: Fri, 10 Jan 2014 18:06:45 -0500 (GMT-05:00)

Some of the automagically created special array variables (GROUPS and DIRSTACK 
for soer; perhaps others) appear to not be fully initialized. Their values 
don't appear correctly in some corner cases until they've been referenced with 
parameter expansion (I think that's the triggering criteria, anyway). The 
following shell dialog illustrates:
~ $ # Start a new shell.
~ $ bash
~ $ bash --version | head -n1
GNU bash, version 4.2.45(1)-release (i686-pc-linux-gnu)
~ $ # Look at some array variables with 'set'.
~ $ set | grep 'GROUPS\|DIRSTACK'
DIRSTACK=()
GROUPS=()
~ $ # Hmm. Empty? Really?
~ $ echo address@hidden
1000 11 14 18 19 20 27 35 80 85 100 250 995 996 10 1003 1013
~ $ echo address@hidden
~
~ $ # Okay, not empty.
~ $ # Look at 'em again with set.
~ $ set | grep 'GROUPS\|DIRSTACK'
DIRSTACK=([0]="~")
GROUPS=([0]="1000" [1]="11" [2]="14" [3]="18" [4]="19" [5]="20" [6]="27" 
[7]="35" [8]="80" [9]="85" [10]="100" [11]="250" [12]="995" [13]="996" 
[14]="10" [15]="1003" [16]="1013")
~ $ # Hmm again. Now shown correctly.
~ $ exit
exit

So far the Bash source code is a somewhat abstruse to me so I thought I'd ask 
for a little help.

Thanks in advance.

- John





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