Issue 7049027: A less wordy version of r85947 and r85948

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Issue 7049027: A less wordy version of r85947 and r85948 (Closed)

Created:
9 years, 7 months ago by Mark Mentovai

Modified:
9 years, 7 months ago

Reviewers:
TVL

CC:
chromium-reviews

Base URL:
svn://svn.chromium.org/chrome/trunk/src/

Visibility:
Public.

Description

A less wordy version of r85947 and r85948. BUG=83180 TEST=none Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=86039

Patch Set 1 #

Total comments: 2

Created: 9 years, 7 months ago

Download [raw] [tar.bz2]

		Unified diffs	Side-by-side diffs	Delta from patch set	Stats (+3 lines, -3 lines)			Patch
	M	chrome/installer/mac/dirdiffer.sh	View		1 chunk	+2 lines, -2 lines	2 comments	Download
	M	chrome/installer/mac/keystone_install.sh	View		1 chunk	+1 line, -1 line	0 comments	Download

Messages

Total messages: 3 (0 generated)

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TVL

lg http://codereview.chromium.org/7049027/diff/1/chrome/installer/mac/dirdiffer.sh File chrome/installer/mac/dirdiffer.sh (right): http://codereview.chromium.org/7049027/diff/1/chrome/installer/mac/dirdiffer.sh#newcode164 chrome/installer/mac/dirdiffer.sh:164: : ${DIRDIFFER_NO_DIFF:=} i'll trust you on this syntax, ...

9 years, 7 months ago (2011-05-20 02:14:01 UTC) #2

Mark Mentovai

9 years, 7 months ago (2011-05-20 02:26:35 UTC) #3

http://codereview.chromium.org/7049027/diff/1/chrome/installer/mac/dirdiffer.sh
File chrome/installer/mac/dirdiffer.sh (right):

http://codereview.chromium.org/7049027/diff/1/chrome/installer/mac/dirdiffer....
chrome/installer/mac/dirdiffer.sh:164: : ${DIRDIFFER_NO_DIFF:=}
TVL wrote:
> i'll trust you on this syntax, it isn't one I've seen before.

:= does an assignment within the expansion if the variable is unset or empty.
The : up front just tells the shell to throw away the result of the expansion.
So the shell does the expansion, which does the assignment, and then chucks it
out. If the variable started off as unset (or empty), it’ll wind up set (or
reset) to empty. Exactly what we want.

mark@rj bash$ declare -p VAR && echo "${VAR}"
-bash: declare: VAR: not found
mark@rj bash$ : ${VAR:=}
mark@rj bash$ declare -p VAR && echo "${VAR}"
declare -- VAR=""

mark@rj bash$ VAR=yes
mark@rj bash$ : ${VAR:=}
mark@rj bash$ declare -p VAR && echo "${VAR}"
declare -- VAR="yes"
yes

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