Difference between single and double quotes in Bash

Question

In Bash, what are the differences between single quotes (`''`) and double quotes (`""`)?

Accepted Answer

Single quotes won't interpolate anything, but double quotes will. For example: variables, backticks, certain `\` escapes, etc.

Example:

```
$ echo "$(echo "upg")"
upg
$ echo '$(echo "upg")'
$(echo "upg")
```

The Bash manual has this to say:

3.1.2.2 Single Quotes

Enclosing characters in single quotes (`'`) preserves the literal value of each character within the quotes. A single quote may not occur between single quotes, even when preceded by a backslash.

3.1.2.3 Double Quotes

Enclosing characters in double quotes (`"`) preserves the literal value of all characters within the quotes, with the exception of `$`, ```, `\`, and, when history expansion is enabled, `!`. The characters `$` and ``` retain their special meaning within double quotes (see Shell Expansions). The backslash retains its special meaning only when followed by one of the following characters: `$`, ```, `"`, `\`, or newline. Within double quotes, backslashes that are followed by one of these characters are removed. Backslashes preceding characters without a special meaning are left unmodified. A double quote may be quoted within double quotes by preceding it with a backslash. If enabled, history expansion will be performed unless an `!` appearing in double quotes is escaped using a backslash. The backslash preceding the `!` is not removed.

The special parameters `*` and `@` have special meaning when in double quotes (see Shell Parameter Expansion).

Difference between single and double quotes in Bash

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