如何使用su -c和bash脚本引用psql语句？

Question

I am trying the following statement in a bash script:

su -c  "psql -d myDB-c 'SELECT count(*) AS number, date_trunc('day'::text, users.registerdate) AS registerdate FROM users;'" postgres

The Problem is the 'day' parameter which needs to be quoted, but inside the quotes it doesn't work.

Answer 1

You seem to be attempting to wrap single quotes inside single quotes, which of course you cannot do. 'this'and'that' parses into 'this' followed by an unquoted and followed by 'that' , not into a quoted string this'and'that .

The usual solution is to wrap single quotes in double quotes, or vice versa, so "this'and'that" or 'this"and"that' if substituting double quotes inside the quoted string is acceptable; but here, you already have both, so you can't do that (straightforwardly).

Assuming psql can read commands from stdin, the simple workaround here is to use a here document .

su -c "psql -d myDB-c <<'____HERE' 
    SELECT count(*) AS number,
           date_trunc('day'::text, users.registerdate) AS registerdate
    FROM users;
____HERE" postgres