okamoto@hpcc01.HP.COM (Jeff Okamoto) (09/28/90)
Two more puzzling questions for patchlevel 18: 1. Why does this construct not do what I think it should? exec "/non-existent-file" || die "Can't exec: $!\n"; 2. Why does this construct not work when this script is called from cron? #!/usr/local/bin/perl eval "exec /usr/local/bin/perl -S $0 $*" if $running_under_some_shell; The output here is a message from cron, saying: sh: <first_file_in_home_directory>: execute permission denied (or something like that). -- \ oo The New Number Who, \____|\mm Jeff Okamoto //_//\ \_\ HP Corporate Computing & Services /K-9/ \/_/ okamoto@ranma.corp.hp.com /___/_____\ ----------- (415) 857-6236
lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall) (09/29/90)
In article <1180002@hpcc01.HP.COM> okamoto@hpcc01.HP.COM (Jeff Okamoto) writes:
: Two more puzzling questions for patchlevel 18:
:
: 1. Why does this construct not do what I think it should?
:
: exec "/non-existent-file" || die "Can't exec: $!\n";
Because exec is a list operator, and thus has a lower precedence than ||.
Say this:
exec("/non-existent-file") || die "Can't exec: $!\n";
or
exec "/non-existent-file";
die "Can't exec: $!\n";
: 2. Why does this construct not work when this script is called
: from cron?
:
: #!/usr/local/bin/perl
: eval "exec /usr/local/bin/perl -S $0 $*"
: if $running_under_some_shell;
I don't have enough to go on here, but bear in mind a coupla three things.
First, cron runs without much of a PATH, and the -S switch above
uses PATH to try to locate the script. Second, cron could conceivably
be feeding the text above to /bin/sh through stdin, in which case $0 isn't
going to be meaningful, and you'd probably try to execute the first argument
of $*. Third, if the arguments you're passing contain any whitespace,
you should instead use
eval 'exec /usr/local/bin/perl -S $0 "${1+$@}"'
if $running_under_some_shell;
Hope that helps. You might just invoke perl directly from cron instead
of relying on the eval-exec hack.
Larryokamoto@hpcc01.HP.COM (Jeff Okamoto) (10/03/90)
lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall) says: > Cron could conceivably be feeding the text above to /bin/sh through > stdin, in which case $0 isn't going to be meaningful, and you'd > probably try to execute the first argument of $*. I suspect this is exactly what is happening. Perhaps cron checks the file type and only force-feeds through sh if it isn't a legitimate executable? > If the arguments you're passing contain any whitespace, you should > instead use > eval 'exec /usr/local/bin/perl -S $0 "${1+$@}"' > if $running_under_some_shell; Fortunately, my arguments are vanilla, but I'll remember this. Perhaps this should become the new standard for non-#! machines? As for the original problem, I've tried all the following cron entries and not only do they not work correctly, but they all give me the same error message from cron: 40 10 * * * * /usr/staff/bin/identck.pl 40 10 * * * * /usr/local/bin/perl /usr/staff/bin/identck.pl 40 10 * * * * /usr/local/bin/perl < /usr/staff/bin/identck.pl I've also tried removing the eval/exec (since my machine does understand #!) and that still doesn't work.... -- \ oo The New Number Who, \____|\mm Jeff Okamoto //_//\ \_\ HP Corporate Computing & Services /K-9/ \/_/ okamoto@ranma.corp.hp.com /___/_____\ ----------- (415) 857-6236
vixie@wrl.dec.com (Paul Vixie) (10/04/90)
# > Cron could conceivably be feeding the text above to /bin/sh through # > stdin, in which case $0 isn't going to be meaningful, and you'd # > probably try to execute the first argument of $*. # # I suspect this is exactly what is happening. Perhaps cron checks the # file type and only force-feeds through sh if it isn't a legitimate # executable? Sounds fishy, and stupid, which means that cron is probably doing it. I recommend use of my cron, which can be had from gatekeeper.dec.com's anonymous FTP, in /pub/misc/vixie. This is the released 2.0 version, which was due in comp.sources.unix last month and may appear in 4.4bsd whenever that comes out. -- Paul Vixie DEC Western Research Lab <vixie@wrl.dec.com> Palo Alto, California ...!decwrl!vixie
aem@mthvax.cs.miami.edu (a.e.mossberg) (10/04/90)
In <1990Oct4.064946.25547@wrl.dec.com> vixie@wrl.dec.com (Paul Vixie) writes: >I recommend use of my cron, which can be had from gatekeeper.dec.com's >anonymous FTP, in /pub/misc/vixie. This is the released 2.0 version, >which was due in comp.sources.unix last month and may appear in 4.4bsd >whenever that comes out. I second the recommendation. Vixie's cron is excellent, and I've been using it for awhile now. It is also available from here (mthvax.cs.miami.edu) as ~ftp/pub/VixieCron.shar.Z aem -- aem@mthvax.cs.miami.edu ....................................................... Rose is a rose is a rose. - Gertrude Stein