> $ strace uptime 2>&1 | grep open
Instead, you should do `strace -e open uptime` to select that system call. Like Useless Use of Cat[0], this could be considered a Useless Use of Grep.
[0] https://en.wikipedia.org/wiki/Cat_%28Unix%29#Useless_use_of_...
Edit: Heh, when I went back to continue reading the article this was mentioned on the following line. Oops :)
Meanwhile, strace's -e filter will find exact matches of syscalls that are named on the command line.
Obviously the author wants the second one, but it is hardly useless to grep. And, once you know how to use grep, you know how to do this sort of search for every program ever written. It is nice that strace has its own budget string matching built in... but knowing how strace works only tells you how strace works. Knowing how grep works lets you do this sort of thing to any program that outputs text.
(A lot of work has been done to try and make something as good as "strace -e" but generically; for example, Powershell's Select-Object cmdlet. I have never managed to get that to do anything useful, but they did manage to break grep, erm ... Select-String, in the process. Great work!)
You could always do things the quick-and-dirty way, but does that help you grow as a programmer? You could write Python code that looks like C, like many people do when they come from a C background, or you could learn how to write Pythonic code by reading the documentation and examples.
> Knowing how grep works lets you do this sort of thing to any program that outputs text.
It's worth noting that I could say the same about strace. Once you know strace, you could run it against any program that uses system calls, which by the way, is many. :-)
If you have filenames with newlines you may have other - less nasty - stuff too.
So you either get a reasonable answer in 1s (or 2s if you have short look at the output before counting). Or you spend 1h+ discussing requirements and carefully writing a program that gives a precise answer.
Things to consider:
- how to treat symlinks
- how to treat hardlinks
- what if files are added/removed to/from the directory tree while you scan
- how to react to missing read permissions
- is your regex on the whole path or just on the basename
- ...
As a real-world example for those who are curious, running mkdir twice yields errno 17, EEXIST, which is "File exists"[1]:
root@vbox:~# mkdir directory
root@vbox:~# mkdir directory
mkdir: cannot create directory ‘directory’: File exists
[0] https://en.wikipedia.org/wiki/Everything_is_a_file
[1] https://elixir.bootlin.com/linux/latest/source/include/uapi/...
Speaking as someone who is using Unix-like systems since the days of Santa Cruz Operation and Linux on a 50 MB disk partition - not everything that is permissible is auspicious.
And most often that's because the permissions were too lax to begin with. That's what you get when a bunch of pot-smoking hippies (X) draw your OS specifications.
I avoid using even spaces in file names, for this specific reason.
---
(X) - and I say that in the best way possible, though some may be inclined to disagree.
"...he and brethren were attempting to make a small fortune for themselves by secreting away an item - a printed book - that was easy enough to get in 1640 but near impossible to get in Tristan's age, making it of great worth."
"So you're thieves and chancers," said I approvingly.
"No," he objected.
-- The Rise And Fall Of D.O.D.O. by Neal Stephenson and Nicole Galland
strace -e trace=process
$ strace uptime 2>&1 | grep open
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/proc/uptime", O_RDONLY) = 3
...
$ strace -e open uptime
10:12:14 up 2 days, 18:52, 1 user, load average: 1.22, 1.30, 1.71
+++ exited with 0 +++
$
After digging in the documentation, I finally found something working:
$ strace -e trace=openat uptime
$ strace -e openat uptimeIs probably easier to remember. You can filter from there.