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From: | Jan Schampera |
Subject: | Re: set -x output of test operator is irretating |
Date: | Thu, 31 Jul 2008 18:00:22 +0200 |
User-agent: | Mozilla-Thunderbird 2.0.0.14 (X11/20080509) |
Bob Proulx wrote:
Chet Ramey wrote:Toralf Förster wrote:I'm wondering why in the example (see below) the right side is prefixed with a '\' wheras the left side is unchanged....tfoerste@n22 ~ $ echo "1 2 3 4" | while read a b c d; do [[ "$a" = "$b" || "$a" = "$c" || "$a" = "$d" ]] && echo oops; done+ read a b c d + echo '1 2 3 4' + [[ 1 = \2 ]] + [[ 1 = \3 ]] + [[ 1 = \4 ]]Because the ==/!=/= operators are defined to match the rhs as a pattern unless it's quoted. You quoted the original string, and the `set -x' output is supposed to be re-usable as input, so the trace output is quoted appropriately.Of course that makes sense for the "==" and "!=" cases. But is that true even for the "=" case? For the "=" case I thought it was "STRING1 = STRING2" and not "STRING = PATTERN".
"When the == and != operators are used, the string to the right of the operator is considered a pattern [...]"
From the description for [[ ]]. = and == should make have difference in behaviour. J.
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