grep -v while loop

bobo · #1 (**permalink**) 01-25-2007

alist contain:
a
b
c
d
e

blist contain:
a
b
c

the code:

#!/usr/bin/ksh
cat blist | while read line
do
grep -V "$line" alist > data
done

I expect to get

d
e

for my result but I don't. What is wrong?

reborg · #2 (**permalink**) 01-25-2007

Quote:

Originally Posted by bobo

alist contain:
a
b
c
d
e

blist contain:
a
b
c

the code:

#!/usr/bin/ksh
cat blist | while read line
do
grep -V "$line" alist > data
done

I expect to get

d
e

for my result but I don't. What is wrong?

I would expect you output to be:
b
c
d
e
f
a
c
d
e
f
a
b
d
e

and have no Idea why you are doing something so convoluted, since you appear to be attempting to replicate the behaviour of fgrep -v (or grep -vf)

bobo · #3 (**permalink**) 01-25-2007

What I try to do is to get the different between alist and blist; in this case the result should be:

d
e

My alist is unknown list of data and so is blist. Let's say my alist contains:

e
b
c
a
d

and my blist contains:

c
a
b

Using the code that I have:

#!/usr/bin/ksh
cat blist | while read line
do
grep -V "$line" alist > data
done

What do I have to do to have a data file that contain:

e
d

Please advise! I tried "diff" it is not worked!

ghostdog74 · #4 (**permalink**) 01-25-2007

maybe you have a typo?? its supposed to be grep -v with small 'v', not 'V' ??

milhan · #5 (**permalink**) 01-26-2007

Quote:

Originally Posted by bobo

Using the code that I have:

Code:

#!/usr/bin/ksh
cat blist | while read line
do
  grep -V "$line" alist > data
done

What do I have to do to have a data file that contain:

e
d

Please advise! I tried "diff" it is not worked!

Try this:

Code:

#!/usr/bin/ksh

# mydiff: gets the diff of two files and writes
# the difference to a third file.

cp alist data

cat blist |
while read line
do
  grep -v "$line" data > /tmp/data
  mv /tmp/data data
done

# end mydiff

bobo · #6 (**permalink**) 01-26-2007

It works! Thanks! Are there other ways??? any else?
thanks!

anbu23 · #7 (**permalink**) 01-26-2007

Quote:

Originally Posted by bobo

It works! Thanks! Are there other ways??? any else?
thanks!

Code:

comm -3 file1 file2

Sort the files and then use the above command

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