How to use line that read from file in grep command

Question

I'm sorry for my poor English, first. I want to read a file (tel.txt) that contains many tel numbers (a number per line) and use that line to grep command to search about the specific number in the source file (another file)!

I wrote this code :

dir="/home/mujan/Desktop/data/ADSL_CDR_Text_Parts_A"
file="$dir/tel.txt"
datafile="$dir/ADSL_CDR_Like_Tct4_From_960501_to_97501_Part0.txt"

while IFS= read -r line
do
    current="$line"
    echo `grep -F $current "$datafile" >> output.txt`
done < $file

the tel file sample :

44001547
44001478
55421487

but that code returns nothing! when I declare 'current' variable with literals it works correctly! what happened?!

It is also quite possible that your input file contains DOS carriage returns. If so, this is a duplicate of https://stackoverflow.com/questions/39527571/are-shell-scripts-sensitive-to-encoding-and-line-endings — tripleee, Feb 13 '19 at 13:13
Paste into https://www.shellcheck.net/ for line by line advice. Then use tripleee's solution. All you need is `grep` (and maybe love. ;) — Paul Hodges, Feb 13 '19 at 14:19

tripleee · Accepted Answer · 2019-02-13T13:17:08.210

6

Your grep command is redirected to write its output to a file, so you don't see it on the terminal.

Anyway, you should probably be using the much simpler and faster

grep -Ff "$file" "$datafile"

Add | tee -a output.txt if you want to save the output to a file and see it at the same time.

echo `command` is a buggy and inefficient way to write command. (echo "`command`" would merely be inefficient.) There is no reason to capture standard output into a string just so that you can echo that string to standard output.

edited Feb 13 '19 at 13:17

answered Feb 13 '19 at 13:09

tripleee

175,061
34
275
318

1

Might also want to use grep's `-x` option (if it's available) to make these "full-line" expressions. – ghoti Feb 13 '19 at 13:22
@ghoti Good addition, though it's not clear from the question whether the OP simply forgot to mention this, or if they need something else. – tripleee Feb 13 '19 at 13:23

score 0 · Answer 2 · answered Feb 13 '19 at 13:10

0

Why don't you search for the line var directly? I've done some tests, this script works on my linux (CentOS 7.x) with bash shell:

#!/bin/bash
file="/home/mujan/Desktop/data/ADSL_CDR_Text_Parts_A/tel.txt"

while IFS= read -r line
do
    echo `grep "$line" /home/mujan/Desktop/data/ADSL_CDR_Text_Parts_A/ADSL_CDR_Like_Tct4_From_960501_to_97501_Part0.tx >> output.txt`
done < $file

Give it a try... It shows nothing on the screen since you're redirecting the output to the file output.txt so the matching results are saved there.

answered Feb 13 '19 at 13:10

Bogdan Stoica

4,349
2
23
38

This preserves many of the antipatterns and inefficiencies in the original code. The [useless use of `echo`](http://www.iki.fi/era/unix/award.html#ercho) is particularly sad. – tripleee Feb 13 '19 at 13:11
I know, thank you for pointing it out. I was trying to keep the script in the initial form... But I'll agree, your approach is better – Bogdan Stoica Feb 13 '19 at 13:13

score 0 · Answer 3 · answered Feb 14 '19 at 12:49

You should use file descriptors when reading with while loop.instead use for loop to avoid false re-directions

dir="/home/mujan/Desktop/data/ADSL_CDR_Text_Parts_A"
file="$dir/tel.txt"
datafile="$dir/ADSL_CDR_Like_Tct4_From_960501_to_97501_Part0.txt"

for line in `cat $file`
do
    current="$line"
    echo `grep -F $current "$datafile" >> output.txt`
done

How to use line that read from file in grep command

3 Answers3