In shell, inside of double quotes only a select few chars should be
escaped. If other chars are escaped this has no effect. Correct the list
of chars that need such escaping.
Also, make sure we can read back the stuff we wrote out without loss.
Fixes: #16788
This is partially a refactoring, but also makes many more places use
unlocked operations implicitly, i.e. all users of fopen_temporary().
AFAICT, the uses are always for short-lived files which are not shared
externally, and are just used within the same context. Locking is not
necessary.
Fixes#10659.
This changes the behaviour of parsing environment files to more closely
follow POSIX shell standards.
This has the effect that these variables defined in a file:
VAR1='\value'
VAR2="\value"
Are now interpreted as `\value` instead of interpreting the `\`
character and interpreting them as `value`.
For more information about the behaviour followed, see:
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_02
