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Trying to find out where the . (current directory) entry in PATH originates, I've run bash as follows:

$ env -i /bin/bash --norc -c 'echo $PATH'
/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin:.

Surprisingly, current directory is still listed there. I've then tried using strace to find out what files bash reads, but found nothing relevant:

$ env -i strace -fefile /bin/bash --norc -c 'echo $PATH' |& grep -v ' ENOENT '
execve("/bin/bash", ["/bin/bash", "--norc", "-c", "echo $PATH"], 0x7fff02c40550 /* 0 vars */) = 0
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libtinfo.so.5", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libdl.so.2", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/dev/tty", O_RDWR|O_NONBLOCK) = 3
getcwd("/home/ruslan", 4096)            = 13
openat(AT_FDCWD, "/etc/nsswitch.conf", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libnss_compat.so.2", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libnss_nis.so.2", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libnsl.so.1", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libnss_files.so.2", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin:.
+++ exited with 0 +++

So, where does bash take this default value for PATH?

Ruslan
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  • @muru actually this question doesn't ask what the default values are, it asks where they come from. Neither the question you're marked as duplicating, not any of the answers there discuss this. – Ruslan Oct 22 '18 at 11:27
  • you sure? One answer lists one possible source; `/etc/environment` (which is one candidate, since PATH isn't set in bashrc in Ubuntu by default anyway - so norc is mostly irrelevant), and another suggests it's hardcored in the binary, like you do. – muru Oct 22 '18 at 11:30
  • @muru well, `/etc/environment` is irrelevant because `strace` here doesn't mention it. And OK, I do now see that answer which _supposes_ that the value is hard-coded, although doesn't show direct evidence of this (which could be done either via `strings` or by source code inspection). Point of this question was to know for sure where the value comes from. – Ruslan Oct 22 '18 at 12:29
  • again, you sure? The answer which gives the hard coded value uses `strings`. And no, `/etc/environment` is only irrelevant in this specific invocation. Bash *never* reads it itself. Other applications do, and then start bash with that environment, that's why you'll never see PATH being *set* in any file bash sources in Ubuntu (they all merely add to it). – muru Oct 22 '18 at 13:30
  • @muru notice the `env -i` I used to start `strace`. No one here had any chance of reading `/etc/environment` (unless `strace` did, but that would be strange). As for `strings` — well, yes, I've been too inattentive when reading, sorry. – Ruslan Oct 22 '18 at 14:18

1 Answers1

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It's hard-coded in the bash source code, and is unrelated to any Ubuntu-specific patches. Namely, it's located in config-top.h in the root of the bash source tree:

/* The default value of the PATH variable. */
#ifndef DEFAULT_PATH_VALUE
#define DEFAULT_PATH_VALUE \
  "/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin:."
#endif
Ruslan
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