Unable to understand this strange MySql client behavior.

Question

I'm not sure what's going on here with the line art output by /usr/bin/mysql here.

The problem: I'm unable to redirect the line art (used in creating the table columns) to a file!

First, I do this on my terminal.

[sd@host:~/tmp]
$ mysql -usd sd -e 'select * from loan;'
+---------+--------------+--------+
| loan_no | branch_name  | amount |
+---------+--------------+--------+
| L-11    | Round Hill   |    900 | 
| L-14    | Downtown     |   1500 | 
| L-15    | Perryridge   |   1500 | 
| L-16    | Perryridge   |   1300 | 
| L-17    | Downtown     |   1000 | 
| L-23    | Redwood      |   2000 | 
| L-93    | Mianus       |    500 | 
+---------+--------------+--------+

Now, I want this whole blessed thing printed above captured, so I redirect stdout and stderr to the file 'out', like so:

[sd@host:~/tmp]
$ mysql -usd sd -e 'select * from loan;' >out 2>&1

As you can see below, the line art is completely missing!

[sd@host:~/tmp]
$ cat out
loan_no branch_name amount
L-11    Round Hill 900
L-14    Downtown 1500
L-15    Perryridge 1500
L-16    Perryridge 1300
L-17    Downtown 1000
L-23    Redwood 2000
L-93    Mianus 500

More proof that the line art is REALLY missing! (The -T option prints tabs, if any.)

[sd@host:~/tmp]
$ cat -T out
loan_no^Ibranch_name^Iamount
L-11^IRound Hill^I900
L-14^IDowntown^I1500
L-15^IPerryridge^I1500
L-16^IPerryridge^I1300
L-17^IDowntown^I1000
L-23^IRedwood^I2000
L-93^IMianus^I500

So, my question is, how the heck does mysql know who -- whether a terminal or a text file -- is sucking its output from 'its rear end' :-) ?

Answer 1

Program can determine whether output stream is terminal or not using isatty (3) function.

MySQL uses this information to change its output (see man mysql, "-t" option produces table output for non-interactive mode too)

Answer 2

It knows

The situation is analogous to

$ ls
tom   dick   harry

and

$ ls > out
$ cat out
tom
dick
harry