diff options
| -rw-r--r-- | lib/m4sugar/m4sh.m4 | 66 |
1 files changed, 57 insertions, 9 deletions
diff --git a/lib/m4sugar/m4sh.m4 b/lib/m4sugar/m4sh.m4 index 3b1e9015..6e145956 100644 --- a/lib/m4sugar/m4sh.m4 +++ b/lib/m4sugar/m4sh.m4 @@ -359,16 +359,64 @@ if test -d /proc/$$/fdinfo; then done else - # Shell redirection operations can only tell whether an fd is open, - # not whether it is readable or writable, so this is a last resort. - # `exec >&n` fails in POSIX sh when fd N is closed, but succeeds - # regardless of whether fd N is open in some old shells, e.g. Solaris - # /bin/sh. We can live with that; at least it never fails when fd N - # is *open*. - if (exec 3>&0) 2>/dev/null; then :; else exec 0</dev/null; fi - if (exec 3>&1) 2>/dev/null; then :; else exec 1>/dev/null; fi - if (exec 3>&2) ; then :; else exec 2>/dev/null; fi + # If lsof is available, we can ask it to print just the information + # we want, in a format that's easy to parse. + # We can't run this command inside backquotes; with some shells that + # may cause the parent shell to have a pipe active on fd 0 right when + # lsof scans its file table. + # lsof may exist but not actually work, e.g. if it's restricted to root. + : > as_fd_status.$$ + if command -v lsof > /dev/null 2>&1; then + lsof -a -p $$ -d 0,1,2 -F fa > as_fd_status.$$ 2> /dev/null || : + fi + as_fd_status=`cat as_fd_status.$$` + + if test -n "$as_fd_status"; then + case "$as_fd_status" in *f0?a[ru]*) ;; *) exec 0</dev/null;; esac + case "$as_fd_status" in *f1?a[wu]*) ;; *) exec 1>/dev/null;; esac + case "$as_fd_status" in *f2?a[wu]*) ;; *) exec 2>/dev/null;; esac + else + # BSD fstat can also print the information we want. The same concerns + # re backquotes and privilege restrictions as above apply. + if command -v fstat > /dev/null 2>&1; then + fstat -p $$ -n > as_fd_status.$$ 2> /dev/null || : + fi + + # fstat's output is a fixed space-separated set of columns, not + # designed for machine parsing: + # USER CMD PID FD DEV INUM MODE SZ|DV R/W. + # Pipes and sockets are formatted differently from regular files + # and device nodes, with an unpredictable number of columns in + # between FD and R/W. We just ignore everything after the fd + # and before the last few characters on the line. + # If there are unexpected spaces in the USER or CMD columns, the + # sed program will output nothing and we will go on to the next + # case. + # The first sed 's' command has hard tabs in its arguments. + as_fd_status="`sed -ne '[ + s/[ ][ ]*/ /g + s/ $// + s/^[^ ]* [^ ]* [0-9]* \([012]\)\**.* \([rw][rw]*\)$/f\1,\2,/p + ]' as_fd_status.$$`" + if test -n "$as_fd_status"; then + case "$as_fd_status" in *f0,r,*|*f0,rw,*) ;; *) exec 0</dev/null;; esac + case "$as_fd_status" in *f1,w,*|*f1,rw,*) ;; *) exec 1>/dev/null;; esac + case "$as_fd_status" in *f2,w,*|*f2,rw,*) ;; *) exec 2>/dev/null;; esac + + else + # Shell redirection operations can only tell whether an fd is open, + # not whether it is readable or writable, so this is a last resort. + # `exec >&n` fails in POSIX sh when fd N is closed, but succeeds + # regardless of whether fd N is open in some old shells, e.g. Solaris + # /bin/sh. We can live with that; at least it never fails when fd N + # is *open*. + if (exec 3>&0) 2>/dev/null; then :; else exec 0</dev/null; fi + if (exec 3>&1) 2>/dev/null; then :; else exec 1>/dev/null; fi + if (exec 3>&2) ; then :; else exec 2>/dev/null; fi + fi + fi + rm -f as_fd_status.$$ fi ]) |