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    Note that -eq is arithmetic comparison, so you can even leave the $ out (in [[ .. ]]), and write [[ a -eq b ]]. With string comparison, you need the $, of course, so [[ $a = $b ]] Commented Feb 15, 2019 at 13:05
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    @user000001 good point. Although, of course, it's very possible that you want those expanded. For example, I would expect this to be a match: var1="afoob"; var2="a*b"; [[ $var1 = $var2 ]] && echo match. If you want to use the glob characters without their acting as a glob in a globbing context (such as the [[ ]]) then you need to quote, yes. Commented Feb 15, 2019 at 14:51
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    @ilkkachu, that surprises me. I thought that "bare" variables would only be considered within an array subscript or ((...)) or $((...). It appears to work, but (old grumpy man, enable) I don't like it. Commented Feb 15, 2019 at 16:11
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    @glennjackman, well, sorry to be the one to tell you that, but yeah, the operands to -eq and friends inside [[ ]] are arithmetic contexts, too. :) (Related: Automatic variable expansion inside bash [[ ]] command) Commented Feb 15, 2019 at 16:32
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    For the record, the only universally portable safe places to not quote variables (and other expansions) are the first field of the case statement (but not the patterns to match in the case statement), and in regular variable assignments (but not in variable assignments as part of export). Commented Feb 15, 2019 at 20:09