mysqlコマンドラインクライアントって、自分の出力がパイプかどうかどうやって判定してるんだろ

gistfile1.txt

$ strace -e write /usr/mysql/8.0.30/bin/mysql -S /usr/mysql/8.0.30/data/mysql.sock -P 64080 --prompt="mysql80 \C> " -e "SELECT 1"
write(1, "+---+\n", 6+---+
)                  = 6
write(1, "| 1 |\n", 6| 1 |
)                  = 6
write(1, "+---+\n", 6+---+
)                  = 6
write(1, "| 1 |\n", 6| 1 |
)                  = 6
write(1, "+---+\n", 6+---+
)                  = 6
+++ exited with 0 +++

$ strace -e write /usr/mysql/8.0.30/bin/mysql -S /usr/mysql/8.0.30/data/mysql.sock -P 64080 --prompt="mysql80 \C> " -e "SELECT 1" | cat
write(1, "1\n1\n", 41
1
)                   = 4
+++ exited with 0 +++

ここか

https://github.com/mysql/mysql-server/blob/mysql-8.0.30/client/mysql.cc#L1273-L1278