From: Bastien Roucariès <ro...@debian.org> Document PATH resolution, particularly null sequence and empty PATH
Signed-off-by: Bastien Roucariès <ro...@debian.org> --- man7/environ.7 | 42 ++++++++++++++++++++++++++++++++++-------- 1 file changed, 34 insertions(+), 8 deletions(-) diff --git a/man7/environ.7 b/man7/environ.7 index 8fc26bb92..11f30c332 100644 --- a/man7/environ.7 +++ b/man7/environ.7 @@ -68,7 +68,8 @@ The name of the logged-in user (used by some BSD-derived programs). Set at login time, see section NOTES below. .TP .B LOGNAME -The name of the logged-in user (used by some System-V derived programs). +The name of the logged-in user (used by some System-V derived programs +and POSIX.1-2017). Set at login time, see section NOTES below. .TP .B HOME @@ -94,19 +95,27 @@ for further details of the environment variables). .TP .B PATH -The sequence of directory prefixes that -.BR sh (1) -and many other -programs apply in searching for a file known by an incomplete pathname. -The prefixes are separated by \(aq\fB:\fP\(aq. -(Similarly one has +The list of places that shells and other programs look in to find +a command when given an incomplete pathname. Elements on this +colon-separated (\(aq\fB:\fP\(aq) list may be absolute or relative directory +names or the zero-length string (interpreted as meaning the +current directory, see section BUGS below). +.B PATH +is checked element by element (left to right), applying that directory +name as a prefix to the pathname (if it does not already +end in a slash, the expansion will insert one between +the prefix and the filename), +until a file is found with the appropriate name and execution +permissions. +.IP +Similarly one has .B CDPATH used by some shells to find the target of a change directory command, .B MANPATH used by .BR man (1) -to find manual pages, and so on) +to find manual pages, and so on. .TP .B PWD The current working directory. @@ -254,6 +263,9 @@ and are specified by POSIX.1-1996 and should be reasonably portable. +.PP +.B PATH +behavior is specified by POSIX.1-2017. .SH NOTES The .BR prctl (2) @@ -292,6 +304,12 @@ preserves all the variables from the existing shell, and or .I su -l is the recommended way of getting a full root environment. +.PP +The default search path (used when the environment +does not contain the variable \fBPATH\fR) +shows some variation across systems. See +.B execlp (3) +for documentation of the exact behavior. .SH BUGS Clearly there is a security risk here. Many a system command has been @@ -330,6 +348,13 @@ The authors of .I gzip should consider renaming their option to .BR GZIP_OPT . +.PP +A zero-length element in +.B PATH, +which appears as two adjacent colons \(aq\fB::\fP\(aq or as a leading +or trailing colon on the list, is replaced by implicit \(aq\fB.\fP\(aq. +In order to be portable and strictly conformant to POSIX.1-2017, a user +should use instead an explicit \(aq\fB.\fP\(aq. .SH SEE ALSO .BR bash (1), .BR csh (1), @@ -343,6 +368,7 @@ should consider renaming their option to .BR execve (2), .BR clearenv (3), .BR exec (3), +.BR execlp (3), .BR getenv (3), .BR putenv (3), .BR setenv (3), -- 2.29.2
