Path Isn't Real on Linux
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Path Isn't Real on Linux
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Re: Path Isn't Real on Linux
#2This actually helps explain some behaviors I’ve encountered. It was never a serious issue, since the answer is to use a full path. But is slightly annoying none the less. Understanding helps a lot.
Re: Path Isn't Real on Linux
#3Why would the author think that the PATH environment variable is being used by the kernel? What an odd assumption.
Re: Path Isn't Real on Linux
#4Why would the author think that the PATH environment variable is being used by the kernel? What an odd assumption.
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Re: Path Isn't Real on Linux
#5Path globbing, pipes, redirection, job control (fg/bg), and all shell variables -- not just $PATH -- are all handled by the shell.
The kernel has no idea what the current process' environment $PATH is, and doesn't even parse any process environment variables at all.
Re: Path Isn't Real on Linux
#6Using "#!sh" at the top of the file does work, but not predictably. It may execute sh in your current directory, which is what Linux does, but your shell may override that (zsh does if the first attempt fails). So it works, but not the way you want it to.
And I'm sure other kernels do other things too.
Re: Path Isn't Real on Linux
#7Why would strace cat be useful here? By the time cat runs, it was obviously already found.
It is basic knowledge that PATH is used by a command interpreter to locate the pathname of binaries. This is true for Window's cmd.exe as well. I never heard of a system where locating files for execution was performed by a kernel.
Re: Path Isn't Real on Linux
#8It's real, it's just implemented by the shell -- same as all Unix-like operating systems. Heck, same as Windows.
Re: Path Isn't Real on Linux
#9Why would the author think that the PATH environment variable is being used by the kernel? What an odd assumption.
Well, execve(2) and execvp(3) are both "system" functions. C (which is already black magic for some people) invokes both by calling into functions exported from libc. If you're not super dorky^Wfamiliar with low-level systems stuff, you might guess that the two functions are implemented in the same place and in the same way. That the latter is just a libc wrapper around the former that does a PATH search is arcane detail you don't have to care about 99% of the time.
It's hard to appreciate how the world looks before you learn a fact. You can't unsee things.
Re: Path Isn't Real on Linux
#10Why would the author think that the PATH environment variable is being used by the kernel? What an odd assumption.
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