On Mon, 26 Jul 2004, David Cary Hart wrote:
Bash is astonishingly fussy about spacing and punctuation.
Here's a (admittedly very inelegant) snippet of code to automatically generate exploit abuse complaints from a cron job.
while read evil freq ; do if [ "$freq" -gt 250 ] ; then a=`host $evil` c=`expr "$a" : '.*\(\..*\.net\)'` evilisp=${c/\./abuse\@} if [ $evilisp > "0" ] ; then . . . . .
Note the use of both ' and ` in the line with the "expr." I find that they are not interchangeable. Assigning a variable to an 'expr' will not work without the "`". In fact, I cut and pasted it from some web docs. I'm not even really sure what character it is.
it's short for "command substitution", which runs the command contained with the ` quotes and produces what's printed to standard output. *very* different from the regular single quotes -- you *bet* they're not interchangeable.
to avoid confusion, you can also identify command substitution with the syntax $(... command ...), which i personally prefer, since it's much clearer. that is, you'd be better off writing:
c=$(expr ... ')
at least, in my opinion.
rday
