Using grep in a if-else statement

Question

Why my code isn't outputting if a string entered isn't in the file. When I enter a string and it isn't in the file, there's no response back, it re-loops back to the beginning. Can someone tell me what's wrong with my code?

while :
do
echo "Please enter a string"
read input_string
echo "Please enter the file name too see if that string is present in it - (Enter .abw after)"
read input_string1
if grep -q $input_string $input_string1 ; then
echo  "Your string has been found"
fi
done

It was meant to say that a string which you enter, it looks for it in the file and it says if that string is present. I've now realised that I need to enter another bit of code for else. Thanks — Adam Poyser, Sep 22 '14 at 12:46
`input_string` isn't really a speaking variable name, by the way :) — Marian, Sep 22 '14 at 17:12
You need double quote around variable expansions. Read [Why does my shell script choke on whitespace or other special characters?](http://unix.stackexchange.com/questions/131766/why-does-my-shell-script-choke-on-whitespace-or-other-special-characters) — Gilles 'SO- stop being evil', Sep 23 '14 at 23:02

GMaster · Answer 1 · 2014-09-24T05:36:17.230

10

while :
 do
     echo "Please enter a string"
     read input_string
     echo "Please enter the file name too see if that string is present in it - (Enter .abw after)"
     read input_string1
     grep -q "${input_string}" "${input_string1}"                                                                 
     if [ $? -eq 0 ] ; then
         echo  "Your string has been found"
     else 
         echo "Your string has not been found"
     fi
 done

edited Sep 24 '14 at 05:36

answered Sep 22 '14 at 12:46

GMaster

5,992
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1

I've just tried this code and it works thanks! I didn't realise that all my problem was with not having an else statement. Thanks for the quick response – Adam Poyser Sep 22 '14 at 12:53
2

You need to quote grep parameters. Think what would happen if my search string includes `-v`, or there are spaces in the filename. – Ángel Sep 22 '14 at 19:33

score 0 · Answer 2 · edited Sep 22 '14 at 17:13

0

You figured out your missing else-branch, but one suggestion:

instead of using $input_string $input_string1 try ${input_string} ${input_string1} just to make sure you don't get $input_string followed by 1.

edited Sep 22 '14 at 17:13

Ghanima

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answered Sep 22 '14 at 16:56

user85015

9
1

No, your proposed replacement is exactly equivalent to the original. `$input_string1` is the value of the variable `input_string1` (split and globbed, since it isn't quoted), it doesn't involve the variable `input_string`. – Gilles 'SO- stop being evil' Sep 23 '14 at 23:00

Using grep in a if-else statement

2 Answers2

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