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Script to check a file and replace some of the contents

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# 1  
Old 03-23-2009
Script to check a file and replace some of the contents
Hi


I have a file that looks like this:


Code:
 
Line            0
animal         elephant
Line            1
animal         elephant
Line            2
animal         elephant
Line            3
animal         elephant

What i am aiming to do is with a script and an input value of a number between 0-3 is to change the elephant to dog so running the script with ./script.sh 2 will change the file so it looks like this


Code:
 
 
Line            0
animal         elephant
Line            1
animal         elephant
Line            2
animal         dog
Line            3
animal         elephant

So far i have this but it fails on "if [ $i -eq $CHANGE ]; then"


Code:
 
#!/bin/bash
NEXTLINE=0
#change internal field separator 
IFS=$'\n'
for i in $(cat inputfile); 
do
echo $i
if [ $NEXTLINE -eq $CHANGE ]; then
sed s/"animal         elephant"/"animal         dog"/ inputfile
exit 0
fi
if [ $i -eq $CHANGE ]; then
NEXTLINE=1
fi
done

I am not sure how to test if the line with Line 2 actually contains the value 2 in it, i'm guessing grep would be handy but i'm not really a scripter so I am a bit stuck. When the correct line with Line x is found then set NEXTLINE and go to the next line thru the for statement and then use sed to change the value.

I have had the following sugguested
Code:
# awk -v n="2" '/Line/ && $NF==n{print;getline;$NF=n;print;next}1' file

but don't understand how to use it.

Any help would be much appreciated.

Note: I have change the value of the data in the inputfile to something generic.

Thank you
Tara
# 2  
Old 03-23-2009
Code:
awk -v n="2" -v var="dog" '$2 == n {print;getline;sub("elephant","dog")}1' file

Regards
# 3  
Old 03-23-2009
thank you Franklin52

that worked great

cheers Smilie
# 4  
Old 03-24-2009
Hi Franklin,

Could you pls explain a bit on what each component in this line tells,

awk -v n="2" -v var="dog" '$2 == n {print;getline;sub("elephant","dog")}1' file
I know about the -v option, that it assigns a value to program variable but the other components are not clear.
# 5  
Old 03-24-2009
Quote:
Originally Posted by santoshbr4
Hi Franklin,

Could you pls explain a bit on what each component in this line tells,

awk -v n="2" -v var="dog" '$2 == n {print;getline;sub("elephant","dog")}1' file
I know about the -v option, that it assigns a value to program variable but the other components are not clear.
Code:
$2 == n {print;getline;sub("elephant","dog")}1

If the 2nd field is equal to n then print the current line, get the next line and substitute "elephant" with "dog".
The getline function is similar to the next statement but it don't pass the controle back to the top of the script.
The "1" is evaluated as true and the default action of awk is to print the current line, similar to {print}.

Regards
# 6  
Old 03-24-2009
Thank You very much.

Regards,
Santosh
# 7  
Old 03-25-2009
a.sh
Code:
sed -n '/'$1'\s*$/ !{
p
}
/'$1'\s*$/ {
        p
        n
        s/elephant/dog/
        p
}' filename

usage
Code:
./a.sh 2
./a.sh 3

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