CODEWITHSUNDEEP
linuxshell
Genelia D'souza
Genelia D'souza

Reputation: 125

Assignment of variables in shell scripting

I am trying to write a shell script to simulate the following problem:

File A contains some entries like 

a  
b  
c

and File B contains 

a  
g  
d  
t  
q  
c

the final file should have
(contents of file b which are not there in file a) 

g  
d  
t  
q

I was trying something like this but it's not working:

for i in `cat b` ; do if[ (grep $i a) != $i ] then echo $i; done

Upvotes: 0

Views: 115

Answers (4)

Vijay
Vijay

Reputation: 67301

pearl.260> cat file3
i
a
b
c
pearl.261> cat file4
a
g
d
t
q
c
pearl.262> nawk 'FNR==NR{a[$1];next}!($1 in a)' file3 file4
g
d
t
q
pearl.263>

Upvotes: 0

xuqin1019
xuqin1019

Reputation: 202

You code has some errors:

  1. forgot the closure of if statement : fi

  2. "grep $i a" must be interpreted as a command , such as $(grep $i a) or `grep $i a`

  3. You must add some characters around $(grep $i a) avoid empty string comparasion , such as ":" or something else, whatever.

Solution:

for i in `cat b` ; do if [ :$(grep $i a) != :$i ] ;then echo $i;fi; done

Upvotes: 2

Jonathan Leffler
Jonathan Leffler

Reputation: 755016

Sort the files and then use comm. In bash:

comm -13 <(sort a) <(sort b)

This assumes you have a sufficiently recent bash (version 3.2 on Mac OS X 10.7.3 is not new enough; 4.1 is OK), and that your files are a and b. The <(sort a) is process substitution; it runs sort on a and the output is sent to comm as the first file; similarly for <(sort b). The comm -13 option suppresses the lines only in the first file (1, aka a) and in both files (3), thus leaving the lines only in 2 or b.

Your command:

for i in `cat b` ; do if[ (grep $i a) != $i ] then echo $i; done

shows a number of problems — four separate syntactic issues:

  1. Space before [
  2. Dollar before (
  3. Semicolon before echo
  4. fi; before done

Fixing them gives:

for i in `cat b`; do if [ $(grep $i a) != $i ]; then echo $i; fi; done

You could also use:

for i in `cat b`
do
    if grep $i a > /dev/null
    then : in both files
    else echo $i
    fi
done

Upvotes: 2

Shiplu Mokaddim
Shiplu Mokaddim

Reputation: 57690

Assuming A and B is your files, it can be done by diff

diff A B | grep '^>' | cut -d ' ' -f 2-

Upvotes: 1

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