The radare2 search engine is based on work done by esteve, plus multiple features implemented on top of it. It supports multiple keyword searches, binary masks, hexadecimal. It automatically flags search hit entries to ease future referencing.
Search is initiated by / command.
[0x00000000]> /?
Usage: /[amx/] [arg]
/ foo\x00 search for string `foo\0`
/w foo search for wide string `f\0o\0o\0`
/wi foo search for wide string ignoring case `f\0o\0o\0`
/! ff search for first occurrence not matching
/i foo search for string `foo` ignoring case
/e /E.F/i match regular expression
/x ff0033 search for hex string
/x ff..33 search for hex string ignoring some nibbles
/x ff43 ffd0 search for hexpair with mask
/d 101112 search for a deltified sequence of bytes
/!x 00 inverse hexa search (find first byte != 0x00)
/c jmp [esp] search for asm code (see search.asmstr)
/a jmp eax assemble opcode and search its bytes
/A search for AES expanded keys
/r sym.printf analyze opcode reference an offset
/R search for ROP gadgets
/P show offset of previous instruction
/m magicfile search for matching magic file (use blocksize)
/p patternsize search for pattern of given size
/z min max search for strings of given size
/v[?248] num look for a asm.bigendian 32bit value
// repeat last search
/b search backwards
Because everything is treated as a file in radare2, it does not matter whether you search in a socket, a remote device, in process memory, or a file.