How to parse /proc/pid/cmdline

Question

I\'m trying to split the cmdline of a process on Linux but it seems I cannot rely on it to be separated by \'\\0\' characters. Do you know why sometimes the \'\\0\' character is

Answer 1

use strings

$ cat /proc/self/cmdline | strings -1
cat
/proc/self/cmdline

Answer 2

The /proc/PID/cmdline is always separated by NUL characters.

To understand spaces, execute this command:

cat -v /proc/self/cmdline "a b" "c d e"

EDIT: If you really see spaces where there shouldn't be any, perhaps your executable (intentionally or inadvertently) writes to argv[], or is using setproctitle()?

When the process is started by the kernel, cmdline is NUL-separated, and the kernel code simply copies the range of memory where argv[] was at process startup into the output buffer when you read /proc/PID/cmdline.

Answer 3

The command line arguments in /proc/PID/cmdline are separated by null bytes. You can use tr to replace them by new lines:

tr '\0' '\n' < /proc/"$PID"/cmdline

Answer 4

Use

cat /proc/2634/cmdline | tr "\0" " "

to get the args separated by blanks, as you would see it on a command line.

Answer 5

Have a look at my answer here. It covers what I found when trying to do this myself.

Edit: Have a look at this thread on debian-user for a bash script that tries its best to do what you want (look for version 3 of the script in that thread).

Answer 6

Super-simple (but for only one process, not bulk parsing, etc):

$ cat /proc/self/cmdline "a b" "cd e" | xargs -0

How it works: by default, xargs just echo'es its input, and switch -0 allows it to read null-separated lines rather than newline-separated ones.