You can compare data using the c command. It accepts an input in various formats and compares the input against the bytes in the current seek.
[0x00404888]> c?
|Usage: c[?dfx] [argument]
| c [string] Compares a plain with escaped chars string
| cc [at] [(at)] Compares in two hexdump columns of block size
| c4 [value] Compare a doubleword from a math expression
| c8 [value] Compare a quadword from a math expression
| cx [hexpair] Compare hexpair string
| cX [addr] Like 'cc' but using hexdiff output
| cf [file] Compare contents of file at current seek
| cg[o] [file] Graphdiff current file and [file]
| cu [addr] @at Compare memory hexdumps of $$ and dst in unified diff
| cw[us?] [...] Compare memory watchers
| cat [file] Show contents of file (see pwd, ls)
| cl|cls|clear Clear screen, (clear0 to goto 0, 0 only)
An example of memory comparision:
[0x08048000]> p8 4
7f 45 4c 46
[0x08048000]> cx 7f 45 90 46
Compare 3/4 equal bytes
0x00000002 (byte=03) 90 ' ' -> 4c 'L'
[0x08048000]>
Another subcommand of c (compare) command is cc which stands for 'compare code'.
[0x4A13B8C0]> cc 0x39e8e089 @ 0x4A13B8C0
[0x08049A80]> cc sym.main2 @ sym.main
c8 compares a quadword from the current seek (0x00000000) from a math expression
[0x00000000]> c8 4
Compare 1/8 equal bytes (0%)
0x00000000 (byte=01) 7f ' ' -> 04 ' '
0x00000001 (byte=02) 45 'E' -> 00 ' '
0x00000002 (byte=03) 4c 'L' -> 00 ' '
The number paramater can of course also be a math expressions using flag names and so on:
[0x00000000]> cx 7f469046
Compare 2/4 equal bytes
0x00000001 (byte=02) 45 'E' -> 46 'F'
0x00000002 (byte=03) 4c 'L' -> 90 ' '
We can use the compare command to compare the current block to a file previously dumped to disk.
r2 /bin/true
[0x08049A80]> s 0
[0x08048000]> cf /bin/true
Compare 512/512 equal bytes