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Enclosing characters in double quotes (‘"’) preserves the literal value of all characters within the quotes, with the exception of ‘$’, ‘`’, ‘\’, and, when history expansion is enabled, ‘!When the shell is in POSIX mode (see Bash POSIX Mode), the ‘!’ has no special meaning within double quotes, even when history expansion is enabled. The dollar sign ( $ ) and backticks ( ` ) characters can able to keep their special meaning within double quotes. This is convenient when you do not want to use the escape characters to change the way the bash interprets the input string. Single Quotes. All characters within single quotes are interpreted as a string character. Double quotes. No character in the single quote has special meaning. This allows us to use old-style command substitution with backticks and variable substitution (dollar sign) within double quoted strings: Double quotes ( ” ) is another way to preserve the literal value of the characters. Double Quotes. All characters within are interpreted as regular characters except for $ or ` which will be expanded on the shell. In the meantime, all my notes are in the attached text file. Single Quotes First, bash parse the right hand side of assignment to one long string $( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd ) because double quote can appear inside double quotes. This works inside double quotes, or in the absence of quotes. Inserting two double quotes in the middle of the string will cancel out one of them. Bash double quotes inside backticks. In fact, with $() instead of backticks, you should be able to keep the inner double quotes: grep "$(date +"%b %d")" A double quote may be quoted within double quotes by preceding it with a backslash. This can be seen in columns 2 and 3 in the example above. Putting \ in front of a metacharacter removes its special meaning. Backticks within backticks? Double quotes escape most characters, except the double quote " the backtick `, the dollar sign $, the backslash \, and the exclamation mark !. Bash escape quotes – Linux Hint, grep "$(date +'%b %d')". Use when you want to enclose variables or use shell expansion inside a string. All behaviour being studied can be explained by the documentation except for escaping double quotes in an inner backticks string inside a double quoted string. I was at first worried that `date '+%m'` would return a string but apparently expr does the math okay normally, so the problem is how to get it to evaluate an inner set of backticks within the outer set of backticks. Wrapping single quotes inside of double quotes will cancel out the expected behavior of the single quotes in the MySQL Query and instead treat it as part of the string. After then, bash start parsing the command substitution. How can I tell it to evaluate an expression within another expression evaluation? And thus ends the lesson of the quotes. (There are slight differences between the shells on this.) Backslash ( ) can also retain its value when it is used by following backticks, double quote and backslash. Here is an example where backticks and $() behave differently: $ echo "$(echo \"test\")" "test" $ echo "`echo \"test\"`" test My understanding was this is because "backslashes (\) inside backticks are handled in a non-obvious manner" But it seems like this is something else because when I remove outer double quotes the results became similar: 3.1.2.3 Double Quotes. It does not work inside single quotes. I'm sufficiently disturbed by this that instead of coding a fix for the lexer, I will ask the bash maintainers about it first. Addition to the accepted answer: While I generally agree with @l0b0's answer here, I suspect the placement of bare backticks in the "worst to best" list is at least partly a result of the assumption that $(...) is available everywhere. 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