The /proc/PID/cmdline file on procfs-enabled systems contains the NULL-delimited command line arguments used to invoke the specified process (PID).
% cat /proc/self/cmdline /tmp/foo|xxd cat: /tmp/foo: No such file or directory 00000000: 6361 7400 2f70 726f 632f 7365 6c66 2f63 cat./proc/self/c 00000010: 6d64 6c69 6e65 002f 746d 702f 666f 6f00 mdline./tmp/foo.