cat and grep in a bash script do not show results desired.

okos · 11-08-2009, 10:39 PM

Hello
I am writing a script and I ran into a snag.
I want to see if contents in a file exist. Ive been fiddling with this for hours but still no success.

In this example I made, I have a file "doc.txt"
In the file I have:

Quote:

John
Frank
Fred

I wrote this script but there seems to be a problem with the syntax.

Code:

#!/bin/bash
N=1
while test "$N" -le "10" ; do
echo "enter name"; read x
if [ "$(cat doc.txt | grep '$x')" = "" ] ; then
echo "$x does not exist in doc.txt"
else
echo "$x exists in doc.txt"
fi
done
exit

It does not matter what name I enter in I still get the same results.

Quote:

enter name
Joe
Joe does not exist in doc.txt
enter name
John
John does not exist in doc.txt
enter name

There is a problem with

Code:

if [ "$(cat doc.txt | grep '$x')" = "" ] ; then

Any suggestions on how to correct this?

wfh · 11-08-2009, 10:48 PM

There are many ways to do this other than the way you're doing it, however, try changing your script like so:

Code:

  if [ `grep $x doc.txt` ] ; then
    echo "$x exists in doc.txt"
  else
    echo "$x does not exist in doc.txt"
  fi

Note the back-quotes. You're executing what comes in between.

See here for Command Substitution in LDP abs guide.

ghostdog74 · 11-08-2009, 10:57 PM

Code:

grep text file 1>/dev/null && echo "exists" || echo "no"

okos · 11-08-2009, 11:35 PM

wfh,

Quote:

if [ `grep $x doc.txt` ] ; then

is missing a condition and did not work.

Quote:

Originally Posted by ghostdog74

Code:

grep text file 1>/dev/null && echo "exists" || echo "no"

Thanks a bunch it works.

Could you explain && and ||

Here is my actual script: (This is what did not work)

Quote:

########### Add cifs to fstab
if [ "$(cat /etc/fstab | grep '${NAME[$N]}/$LIST')" = "" ] ; then

echo "//${IP[$N]}/$LIST /home/server/${NAME[$N]}/$LIST cifs credentials=/etc/samba/.smbpass,_netdev,uid=1000,gid=1000 0 0" >> /etc/fstab
fi

Perhaps if I change it to:

Quote:

grep grep '${NAME[$N]}/$LIST' /etc/fstab 1>/dev/null && \
echo "//${IP[$N]}/$LIST /home/server/${NAME[$N]}/$LIST cifs credentials=/etc/samba/.smbpass,_netdev,uid=1000,gid=1000 0 0" >> /etc/fstab

bigrigdriver · 11-08-2009, 11:39 PM

Action && condition 1 || condition 2
translates as
Action AND condition OR condition 2