Finding contents of one file in another file

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grep itself is able to do so. Simply use the flag -f:

grep -f <patterns> <file>

<patterns> is a file containing one pattern in each line; and <file> is the file in which you want to search things.

Note that, to force grep to consider each line a pattern, even if the contents of each line look like a regular expression, you should use the flag -F, --fixed-strings.

grep -F -f <patterns> <file>

If your file is a CSV, as you said, you may do:

grep -f <(tr ',' '\n' < data.csv) <file>

As an example, consider the file “a.txt”, with the following lines:

alpha
0891234
beta

Now, the file “b.txt”, with the lines:

Alpha
0808080
0891234
bEtA

The output of the following command is:

grep -f "a.txt" "b.txt"
0891234

You don’t need at all to for-loop here; grep itself offers this feature.

Now using your file names:

#!/bin/bash
patterns="/home/nimish/contents.txt"
search="/home/nimish/another_file.csv"
grep -f <(tr ',' '\n' < "${patterns}") "${search}"

You may change ',' to the separator you have in your file.

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