Shell Scripting finding text in a text file

Question

i am trying to check for a string in a text file. If string1 does not exisit then add string1 after string 2. Else string1 exists do nothing.

Here is what i have so far:

if [ string1 does not exisit ]  //Stuck at this
then
sed '/string2/ a\ string1' myfile
fi

Also how can include the "/" character in my strings?

Dennis Williamson · Accepted Answer · 2011-03-01 17:30:37Z

4

if grep -qs string1 myfile
then
    sed '/string1/ a\ string2' myfile
fi

However, you could skip the if since sed is testing for the existence of the string anyway. That way, you're only reading the file once instead of twice. Use sed -i if you want the change to be made to the file in-place.

answered Mar 1, 2011 at 17:30

Dennis Williamson

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1 Comment

Matt Over a year ago

Sorry i made a typo, sed should be checking for the existence of string2.

krtek · Accepted Answer · 2011-03-01 17:37:32Z

0

You can use grep, for example like this :

$(grep -q "string1" myfile)
if [ $? -eq 1 ]; then
    sed '/string1/ a\ string2' myfile
fi

edited Mar 1, 2011 at 17:37

answered Mar 1, 2011 at 17:32

krtek

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2 Comments

Dennis Williamson Over a year ago

The brackets and command substitution aren't necessary. The -eq 1 won't pass because the exit code is not output, it's held in $?.

krtek Over a year ago

Yeah, you're right, I'll modify the code. Concerning the bracket, I like to put them even if they aren't necessary, I find the code more readable with them.

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