In radare2, the assembler and disassembler logic is implemented in the r_asm_* API, and can be used with the pa and pad commands from the commandline as well as using .

Rasm2 can be used to quickly copy-paste hexpairs that represent a given machine instruction. The following line is assembling this mov instruction for x86/32.

Apart from the specifying the input as an argument, you can also pipe it to rasm2:

The pa and pad are a subcommands of print, what means they will only print assembly or disassembly. In case you want to actually write the instruction it is required to use or wx commands with the assembly string or bytes appended.

The assembler understands the following input languages and their flavors: x86 (Intel and AT&T variants), olly (OllyDBG syntax), (PowerPC), arm and java. For Intel syntax, rasm2 tries to mimic NASM or GAS.

There are several examples in the rasm2 source code directory. Consult them to understand how you can assemble a raw binary file from a rasm2 description.

Now we can assemble it in place:

Assembling also is accessible in radare2 visual mode through pressing key to insert the assembly in the current offset.

The cool thing of writing assembly using the visual assembler interface that the changes are done in memory until you press enter.