CODEWITHSUNDEEP
bashgrep
Vlad Mikhailov
Vlad Mikhailov

Reputation: 13

grep from file doesn't write result to an output file

I'm trying to grep strings from file2.csv using existing strings from file1.csv and write matched lines to result.csv file. A have a following bash script:

cat file1.csv | while read line; do
    grep $line ./file2.csv > result.csv
done

But afterall the result.csv is always empty. When I do manual grep from file2.csv everything works fine. What I do wrong?

file1.csv:

15098662745072
15098662745508

file2.csv:

";"0";"15098662745072";"4590";"4590";"
";"0";"15098662745508";"6400";"6400";"
";"0";"15098662745515";"6110";"6110";"
";"0";"15098662745812";"7970";"7970";"

expected result (result.csv):

";"0";"15098662745072";"4590";"4590";"
";"0";"15098662745508";"6400";"6400";"

Upvotes: 1

Views: 378

Answers (2)

Ed Morton
Ed Morton

Reputation: 203324

You should be using awk for this, not grep, because:

a) grep does not by default look for strings, it looks for regular expressions. You need to use fgrep or grep -F or awk instead of grep to search for strings.

b) You really only want to match the numbers from file1.csv when they appear as a full specific field in file2.csv, not wherever they occur on the line.

awk -F'";"' 'NR==FNR{a[$0];next} $3 in a' file1.csv file2.csv > result.csv

Upvotes: 1

dogbane
dogbane

Reputation: 274562

> keeps overwriting the file. Use >> to append to it.

Instead of using a loop, you can simply use the -f option in grep to make grep read patterns from the file.

grep -f file1.csv file2.csv > result.csv

If you have to use a loop, use the following approach:

while read line; do
    grep "$line" ./file2.csv
done < file1.csv > result.csv

Upvotes: 4

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