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Challenging Script

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dave_nithis dave_nithis is offline

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Challenging Script

Nov 16th, 2007

Hi all,

I have two files namely
a.txt
b.txt
a.txt contains 100 records and b.txt contains 9 records.These 9 records in b.txt is also present in a.txt.So,I need a script that compares these two files and outputs the unique 91 records alone in another file.

Thanks to all in advance!!!!

Regards
dave.

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masijade

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Re: Challenging Script

Nov 16th, 2007

Cool. What do you have so far, and what problem are you having with it.

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Re: Challenging Script

Nov 16th, 2007

I am trying to do this.But i dont know how to do the comparison part.

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Re: Challenging Script

Nov 16th, 2007

Also am trying this in microsoft Access.

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masijade

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Re: Challenging Script

Nov 16th, 2007

•

Originally Posted by dave_nithis

Also am trying this in microsoft Access.

What do you mean by this? This forum is for Linux/Unix Shell Scripting, not Windows Batching (unless things have changed).

As far as doing the comparisons, an easy, but not necessarily performant way is a simple grep command.

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eggi

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Re: Challenging Script

Nov 17th, 2007

a's got 100
b's got 9
you need the 91 uniques - I'll put 'em in c.txt

 Help with Code Tags 
 Shell Scripting Syntax (Toggle Plain Text) 
while read line
do
   grep $line b.txt >/dev/null 2>&1               
   if [ $? -ne 0 ]
   then
       echo $line >>c.txt
   fi
done <a.txt
while read line
do
   grep $line b.txt >/dev/null 2>&1               
   if [ $? -ne 0 ]
   then
       echo $line >>c.txt
   fi
done <a.txt

Sorry - just needed to drop a post somewhere - it's been a while

, Mike

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masijade

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Re: Challenging Script

Nov 17th, 2007

•

Originally Posted by eggi

a's got 100
b's got 9
you need the 91 uniques - I'll put 'em in c.txt
Help with Code Tags

Shell Scripting Syntax (Toggle Plain Text)
while read line
do
   grep $line b.txt >/dev/null 2>&1               
   if [ $? -ne 0 ]
   then
       echo $line >>c.txt
   fi
done <a.txt
while read line do grep $line b.txt >/dev/null 2>&1 if [ $? -ne 0 ] then echo $line >>c.txt fi done <a.txt
Sorry - just needed to drop a post somewhere - it's been a while

, Mike

Its actually easier, if with a few more file operations.

 Help with Code Tags 
 Shell Scripting Syntax (Toggle Plain Text) 
cp b.txt /tmp/b1.txt
while read line
do
   grep -v $line /tmp/b1.txt >/tmp/b2.txt 2>/dev/null
   mv -f b2.txt b1.txt
done <a.txt
mv b1.txt c.txt
cp b.txt /tmp/b1.txt
while read line
do
   grep -v $line /tmp/b1.txt >/tmp/b2.txt 2>/dev/null
   mv -f b2.txt b1.txt
done <a.txt
mv b1.txt c.txt

Last edited by masijade; Nov 17th, 2007 at 5:58 am.

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dave_nithis dave_nithis is offline

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Re: Challenging Script

Nov 19th, 2007

Masijade,

I finished the file comparison in MS Access.But I am trying to do the same file comparison using Shell script...Thats why posted you a thread..

I didn't understand this line in your script :
grep -v $line /tmp/b1.txt >/tmp/b2.txt 2>/dev/null

Can you please explain?

Thanks in advance
Regards
dave.....

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dave_nithis dave_nithis is offline

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Re: Challenging Script

Nov 19th, 2007

•

Originally Posted by eggi

a's got 100
b's got 9
you need the 91 uniques - I'll put 'em in c.txt
Help with Code Tags

Shell Scripting Syntax (Toggle Plain Text)
while read line
do
   grep $line b.txt >/dev/null 2>&1               
   if [ $? -ne 0 ]
   then
       echo $line >>c.txt
   fi
done <a.txt
while read line do grep $line b.txt >/dev/null 2>&1 if [ $? -ne 0 ] then echo $line >>c.txt fi done <a.txt
Sorry - just needed to drop a post somewhere - it's been a while

, Mike

Mike,

why are you using ">/dev/null 2>&1" in your script?
What condition you are checking in your "if" loop?

Regards
Dave

Last edited by dave_nithis; Nov 19th, 2007 at 7:57 am.

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masijade

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Re: Challenging Script

#10

Nov 19th, 2007

•

Originally Posted by dave_nithis

Masijade,

I finished the file comparison in MS Access.But I am trying to do the same file comparison using Shell script...Thats why posted you a thread..

I didn't understand this line in your script :
grep -v $line /tmp/b1.txt >/tmp/b2.txt 2>/dev/null

Can you please explain?

Thanks in advance
Regards
dave.....

grep -v means to match everything except the next text (you should probably place $line in quotes) from the the first file listed (b1.txt) and output it to the second file listed ( > b2.txt) and ignore any error messages (2>/dev/null).

The next line then moves b2.txt to b1.txt so you can repeat the procedure with the next line. Once you have gone through all lines, b2.txt contains all lines from b that were not in a.