In Linux:
1) find where is sqlplus located,
[oracle@LINUX db_1]$ `which sqlplus`
/app/oracle/product/11.2.0/db_1/bin/sqlplus
2) Determine the file type,
[oracle@LINUX db_1]$ file /app/oracle/product/11.2.0/db_1/bin/sqlplus
/app/oracle/product/11.2.0/db_1/bin/sqlplus: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs). For GNU/Linux 2.6.18, not stripped.