Conference turris::digital_unix

8973.0. "CRON does not perform command substitution after > symbol" by NETRIX::"[email protected]" (R.J. Riha") Wed Feb 26 1997 11:06

Versions tested: V3.2G, V4.0B

Have a customer who is trying to perform command line substitution from within
his crontab file:

0 * * * * /usr/users/ao/lnk/lnk.csh > new`date +%a`.log

instead of creating an output file called "newTue.log", it creates "new"

If you do this from the command line (bourne shell), it works:

$ /usr/users/ao/lnk/lnk.csh > new`date +%a`.log
$ ls *.log
newTue.log

It also appears that if the command substitution is performed before the
pipe ">" symbol, it works:

0 * * * * echo The hour is `date`. >/dev/console

Prints:
 The hour is Tue Feb 25 14:00:00 EST 1997 V4.0b system.


According to the Man Page, I see no reason for it not to work on either
side of the pipe symbol:

"Command Substitution

To capture the output of any command as an argument to another command,
  place that command line within ` ` (grave accents).  This concept is known
  as command substitution.  The shell first executes the command or commands
  enclosed within the grave accents, and then replaces the whole expression,
  grave accents and all, with their output.  This feature is often used in
  assignment statements:
     today=`date`

  This statement assigns the string representing the current date to the
  today variable.  The following assignment saves, in the files variable, the
  number of files in the current directory:

       files=`ls | wc -l`

  You perform command substitution on any command that writes to standard
  output by enclosing that command in grave accents.  You can nest command
  substitutions by preceding each of the inside sets of grave accents with a
  \ (backslash):

       logmsg=`echo Your login directory is \`pwd\``"


Thanks,
RJ
[Posted by WWW Notes gateway]

Hi,

Instead of:

	new`date +%a`.log

try:
	new`/usr/bin/date +%a`.log

Cron might not have date in his path.

-Brian
[Posted by WWW Notes gateway]

Re. 1

If cron couldn't find the path to "date", then substituting it into
the command before the pipe symbol should fail also, right?  That is
not the case.  It only fails after the > symbol.

FYI, I did try your suggestion anyway, the behavior (as expected) did
not change.

Thanks

RJ
[Posted by WWW Notes gateway]

Hi

You need a \ before each % symbol! 

0 * * * * /usr/users/ao/lnk/lnk.csh > new`date +\%a`.log

Regards
Lucius
[Posted by WWW Notes gateway]