How to remove a plain text protecting single quote from all the selected cells in LibreOffice Calc?

You can remove the leading single quote (which actually isn't part of the string in the cell) using a regex-based search and replace:

• Search for all characters between the start and end of the string ^.*$
• replace with match &

From the "Data" menu, choose "Text to columns".

An attempt for regex replacing of ^.\*$ with & crashed LibreOffice 5. Replacing of .\* with & worked fine.

This problem with the single quote mark still exists in LibreCalc. I tested both solutions and they work.

Text to Columns is probably the easiest to remember:

Data> Text to Columns> Make sure the settings do not actually split the data, then click OK. ...Done.

Search and Replace might be good if you need to get rid of the leading single quote indicator in the entire sheet:

Edit> Find and Replace> Make sure "regular expressions" is selected then search for.* and replace with & ...Done.

You do not need the ^ and $ characters to indicate the start and end of the string. The dot which means "any character" and the asterisk which means "zero or more times" does the trick.

But be careful; Removing the ' text flag opens up your data to auto-reinterpretation. In my experience, (at least with Excel) this leads to data corruption as it is often not correctly predicted which data should be reformatted and how.