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shell problem: sending variable with multiple flags to a cmd

Answer 1

+2 A:

Don't put the quotes around the variable if you want the words in that variable to be interpreted as separate arguments to the command.

Instead of this:

/usr/sbin/tmpwatch "$flags"

Use this:

/usr/sbin/tmpwatch $flags

Re your comments:

It makes no difference if the script is run from cron. The script is interpreted by sh not cron.

Single-quotes in the shell prevent variable expansion. Otherwise, variables do expand -- whether they're within double-quotes or unquoted. Try it:

$ food=banana
$ echo $food      # echoes banana
$ echo "$food"    # echoes banana
$ echo '$food'    # echoes $food literally

The other effect of quotes, whether single or double, is to make a string be passed to the command as a single word instead of multiple words separated by any whitespace that was in the expanded variable value.

Bill Karwin 2009-08-25 03:35:29

Thanks Bill. The original script (from RedHat) had the quotes (before the passenger directories line was added). Anyhow, I thought the quotes were needed to trigger variable interpolation. Now I know better. Does it make any difference that the script is in /etc/cron.daily for use by crontab? Thanks again, Larry

Larry K 2009-08-25 12:13:03

Answer 2

A:

What Bill said. Here's a crazier to write this, by the way, if you're using bash:

#!/bin/bash    

# Store file names in an array variable. Same as (`ls -d /tmp/passenger*`),
# by the way, but the ls is unnecessary.
files=(/tmp/passenger*)

# Add each file name to $flags, adding -x in front of each.
# "/#/-x " means search for an empty string at the beginning of
# each array item, and replace it with "-x ". Effectively, that
# just prepends "-x " to each.
flags="-umc -v -v ${files[*]/#/-x }"

# No quotes around $flags, so each word is passed as a separate
# command-line argument to tmpwatch.
/usr/sbin/tmpwatch $flags -x /tmp/.X11-unix -x /tmp/.XIM-unix \
    -x /tmp/.font-unix -x /tmp/.ICE-unix -x /tmp/.Test-unix 240 /tmp

From the bash man page:

${parameter/pattern/string}

The pattern is expanded to produce a pattern just as in pathname expansion. Parameter is expanded and the longest match of pattern against its value is replaced with string. If pattern begins with /, all matches of pattern are replaced with string. Normally only the first match is replaced. If pattern begins with #, it must match at the beginning of the expanded value of parameter. If pattern begins with %, it must match at the end of the expanded value of parameter. If string is null, matches of pattern are deleted and the / following pattern may be omitted. If parameter is @ or *, the substitution operation is applied to each positional parameter in turn, and the expansion is the resultant list. If parameter is an array variable subscripted with @ or *, the substitution operation is applied to each member of the array in turn, and the expansion is the resultant list.

John Kugelman 2009-08-25 04:20:15

Thanks John. I'm modifying a RH-supplied system cron file so my assumption is /bin/sh is being used.

Larry K 2009-08-25 12:16:23

`sh` is really `bash` on Red Hat, but you can add `#!/bin/bash` at the top to pick your shell explicitly.

John Kugelman 2009-08-25 15:57:39

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