Execute shell command in a variable

hankta · 08-24-2011, 08:10 PM

I am trying to write a shell script to grab the filename in a directory with that has a specific pattern but having problem when piping grep.

For example:
Patvar=`date +"%Y%m%d" # pattern for grep to search
Fname=`ls /home/abc/ | grep ${Patvar}`
echo " the file is: $Fname"

it returned an empty string!!!
if I used I enter a fix string it will work but not as a variable!

What did I do wrong?

chrism01 · 08-24-2011, 08:33 PM

You missed the final backquote there on the first line.
` cmd ...`

You might find it easier to use the alternate version $(cmd ...)

Code:

Patvar=$(date +"%Y%m%d") # pattern for grep to search
Fname=$(ls /home/abc/ | grep $Patvar )
echo " the file is: $Fname"

The {} in the 2nd line were redundant in this instance.

Tinkster · 08-24-2011, 09:20 PM

Hi, welcome to LQ!

If this is your actual script you're missing a closing back-tick on the
first line. If it's not there's something else not quite right...

Code:

Patvar=$(date +"%Y%m%d")
touch test$(date +"%Y%m%d").txt
Fname=$(ls  | grep ${Patvar})
echo ${Fname}
test20110825.txt

This behaves the same w/ back-ticks.

Cheers,
Tink

P.S.: Darn, I was AFK for too long on that one ;D

hankta · 08-25-2011, 12:10 AM

Thank you - it is working now.

David the H. · 08-25-2011, 01:06 AM

In general, variables are for holding data, not code. That's what functions are for. See here:

http://mywiki.wooledge.org/BashFAQ/050

Also, you should never parse ls for file names. Use find, or globbing, or some other technique.

http://mywiki.wooledge.org/ParsingLs

So a more proper solution would be something like this:

Code:

findbydate() {
	local searchvar=$( date +"%Y%m%d" )
	echo -n /home/abc/*$searchvar*

	# or with find
	#find /home/abc -maxdepth 1 -name "*$searchvar*" -print
}

Fname="$( findbydate )"
echo " the file is: $Fname"