A bit curious about `mysql -e` output format with & without redirect

问题

Say when I run mysql -u user -p -e 'select id from db.users limit 1', I got:

+------+
| id   |
+------+
| 8434 |
+------+

When I redirect the output/stdout to some file, like mysql -u user -p -e 'select id from db.users limit 1' > /tmp/a.txt, then I cat /tmp/a.txt, I got:

id
8434

So where do those little format strings go? Does it mean that mysql knows when it is redirected, so it returns a different format? I always thought a redirect(>) doesn't concern the previous command, that it doesn't have to know if or where its output is redirected. Or is it another explanation?

回答1:

You'll get same output by adding -B option

    mysql -B -u user -p -e 'select id from db.users limit 1'

then you'll see

 id       
 8434 

Also, mysql command tests if the cout is tty or not, to switch output formatting. As you can see in the source code of mysql command.

回答2:

To get the same fancy table format when redirecting, add the -t flag or --table to your mysql command.

+----+--------+
| id | name   |
+----+--------+
|  1 | Quincy |
+----+--------+

As for your question, mysql uses isatty under the hood to know if you are redirecting output.

来源：https://stackoverflow.com/questions/27812190/a-bit-curious-about-mysql-e-output-format-with-without-redirect