Shell Programming and Scripting

i need a favour

if ( grep -i adding mpg* | grep -iv equation | ls -ctr | tail -1 ) # if it is not found

echo "log couldnot find "

else
var='grep -i adding mpg* | grep -iv equation | ls -ctr | tail -1'


for the above i am struggling with syntax
could someone please help me in that

The first problem is that tail doesn't consider "no input" a failure, so you can't use that as a condition directly. But pipe that to grep and you should be ready to go.

Code:

if something | tail -1 | grep .; then ...

What exactly do you hope to accomplish by piping grep to ls? You want the file name from grep where the match occurred? Or what? ls doesn't read its standard input, and grep prints the actual matching line, not the file name of the match. This can be worked around, but having your requirements would help.

Assuming you want the latest file which matches "adding" and "equation", we can come up with something like

Code:

var=`grep -il adding mpg* | xargs grep -ivl equation | xargs ls -ctr | tail -1`
case $var in '') echo "Could not find log" >&2;; esac

grep -l says to print the file name of the match instead of the actual match, and xargs is the way to use the output of a command as the command-line arguments in another command. (You could use backticks, too, but they have some problems.)

You probably want to do something more (like, exit the script maybe) if $var is empty.