Обсуждение: [DOCS] How to prompt for a value if a variable is not set

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Page: https://www.postgresql.org/docs/9.2/static/app-psql.html
Description:

I want to make a small script to show the primary key for a table and put
the name into a variable.

Called from another script, the tablename is set in a variable called
tablename.  But if the variable is not set, I want the script to prompt for
it.

Is there a way to do this?
thx,
-r

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But if the variable is not set, I want the script to prompt for
it.