Shell Script - can't find string in file using grep

Question

I've come across some weird problem that I can't solve by myself. I've got two files, content as follows:

File1.txt

Butterscotch;lkt+4S7Yhzf/g
Sox;WrWMzN6HD
Table;K4yPIK+SFfTFs
tram;YaY3opP9ie
number;e/WwiF5aihUY
Buttler;Nsadlkt+4S7Yhz
wzahwahwah;PYaY3opP9ieH

File2.txt

Butterscotch;lkt+4S7Yhzf/g
Sox;WrWMzN6HD
Table;K4yPIK+SFfTFs
tram;YaY3opP9ie
number;e/WwiF5aihUY

I need to find differences between those two files but only for entries that are before semicolon, so I first use awk to get those entries:

awk 'BEGIN {FS=";"}; {print $1}' File1.txt > Output1.txt
awk 'BEGIN {FS=";"}; {print $1}' File2.txt > Output2.txt

New files contain entries as follows:

Output1.txt

Butterscotch
Sox
Table
tram
number
Buttler
wzahwahwah

Output2.txt

Butterscotch
Sox
Table
tram
number

Then I use grep -Fxvf Output2.txt Output1.txt > Diff.txt to print out the differences between Output2.txt and Output1.txt so my file looks like this:

Diff.txt

Buttler
wzahwahwah

Now the tricky part. I need to find and print out to another file whole lines from File1.txt that start with entries from Diff.txt. I'm declaring a variable and do something like this:

variable=$(cat Diff.txt)
grep $variable Output1.txt > Delete.txt

So for this example I should get something like this:

Delete.txt

Buttler;Nsadlkt+4S7Yhz
wzahwahwah;PYaY3opP9ieH

But unfortunately I get an error:

grep: wzahwahwah: No such file or directory

File Delete.txt instead of desired data contains:

/home/working/File1.txt:Buttler;Nsadlkt+4S7Yhz

So it's far from what I need to get. What I've noticed is that when I remove from File1.txt

wzahwahwah;PYaY3opP9ieH

I get no errors and my desired file looks like:

Buttler;Nsadlkt+4S7Yhz

Any ideas why this isn't working?

anubhava · Accepted Answer · 2014-10-17 07:30:04Z

4

Instead of your cat and subsequent grep use this grep:

grep -Ff Diff.txt File1.txt
Buttler;Nsadlkt+4S7Yhz
wzahwahwah;PYaY3opP9ieH

answered Oct 17, 2014 at 7:30

anubhava

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4 Comments

anubhava Over a year ago

I believe problem is reading file content in a variable and using that variable unquoted afterwards.

NRG Over a year ago

Only thing that bothers me now is why did grep work for other entries, but didn't work for wzahwahwah;PYaY3opP9ieH. Nevertheless once again - thank you.

NRG Over a year ago

Hi, It's me again ;) Everything was working great 'till today. I've noticed that when inside my Diff.txt I have, for example, only one letter t, my Delete.txt file would have all entries that have that letter (so there would be Butterscotch, tram, Buttler). Is there a way to secure this, so grep would get only whole words?

anubhava Over a year ago

Sure you can use: grep -wFf Diff.txt File1.txt Here -w for whole word match.

glenn jackman · Accepted Answer · 2014-10-17 10:38:15Z

2

When you do this

variable=$(cat Diff.txt)
grep $variable Output1.txt > Delete.txt

After the variable is expanded, since it is unquoted the grep command turns into

grep Buttler wzahwahwah Output1.txt > Delete.txt

Grep only uses the first argument as the pattern, and all following args are filenames. Grep found "Buttler" in Output1.txt, but did not find a file named "wzahwahwah"

answered Oct 17, 2014 at 10:38

glenn jackman

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1 Comment

NRG Over a year ago

Thank You for explanation. I've checked all my other scripts where I use grep as I mentioned above, and I'm using it only on files that contain one variable (eg. 0 or 1 to check if script is running or not). So I've made wrong assumption that this will also work with other variables :)

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