Single statements will not insert anything, yet twofold statements will. For instance: factors, backticks, certain \ get away, and so on.
$ reverberation "$(echo "upg")"
$ reverberation '$(echo "upg")'
The Bash manual has this to say:
220.127.116.11 Single Quotes
Encasing characters in single statements (') jelly the exacting worth of each person inside the statements. A solitary statement may not happen between single statements, in any event, when gone before by an oblique punctuation line.
18.104.22.168 Double Quotes
Encasing characters in twofold statements (") jelly the exacting worth of all characters inside the statements, except for $, ', \, and, when history extension is empowered, !. The characters $ and ' hold their exceptional significance inside twofold statements (see Shell Expansions). The oblique punctuation line holds its extraordinary significance just when followed by one of the accompanying characters: $, ', ", \, or newline. Inside twofold statements, oblique punctuation lines that are trailed by one of these characters are taken out. Oblique punctuation lines going before characters without a unique importance are left unmodified. A twofold statement might be cited inside twofold statements by going before it with an oblique punctuation line. Whenever empowered, history extension will be performed except if a ! showing up in twofold statements is circumvented utilizing an oblique punctuation line. The oblique punctuation line going before the ! isn't eliminated.
The unique boundaries * and @ have extraordinary importance when in twofold statements (see Shell Parameter Expansion).