Why not used standart SQL commands?

Hello, I'm seeing \dt used for "show tables", \l used for "show databases". Why not standart SQL syntax words? Why specified PostgreSQL commands? I can't figure out that. Ali

How are md5.h: pg_md5_hash() function and below functions working?

I can't understand functions in md5.h, these are seemingly little bit weird. Such as: /* Utilities common to all the MD5 implementations, as of md5_common.c */ extern bool pg_md5_hash(const void *buff, size_t len, char *hexsum); extern bool pg_md5_binary(const voi