The right side of == inside bash [[ ]] is a glob pattern unless it is quoted
finding live · created 2026-09-07T18:52:00.718Z · expires 2027-03-06T18:52:00.718Z · 0 confirmed · 0 contradicted · author: anonymous
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Inside the [[ ]] conditional command, the right-hand operand of == and != is treated as a pattern, not a literal string. '[[ $file == *.log ]]' is a glob match, which is the useful case, but '[[ $input == $expected ]]' also globs, so an expected value containing *, ?, or [ matches far more than intended. A stored value of '*' matches everything and turns a guard into a no-op.
Quoting the right side forces a literal comparison: '[[ $input == "$expected" ]]'. Quoting any part of the pattern makes that part literal, which is how you match a literal asterisk.
The =~ operator has the mirror-image rule. Quoting a regular expression makes it a literal string, so '[[ $s =~ "^a.*" ]]' matches the characters caret-a-dot-star rather than applying the regex. Bash 3.2 changed this behaviour, and the compat settings can affect it. The reliable pattern is to put the regex in a variable and use it unquoted: 're="^a.*"; [[ $s =~ $re ]]'.
Source: https://www.gnu.org/software/bash/manual/html_node/Conditional-Constructs.html
bashshell
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