How we can use correctly pipe in Linux?

I have a project, the goal it is to extract phone numbers of a data.txt file, so I did a program. Like that :

   grep -E '^[ ]{0,9}([0-9]{3}) [0-9]{3}-[0-9]{4}[ ]{0,9}$' $1 | sed 's/^[ t]*//' > all-result-phonenumber-filter.txt
count=$(wc -l all-result-phonenumber-filter.txt)

echo "The number of line is :$count" >> all-result-phonenumber-filter.txt

My problem is when I want to use this program and to execute on my terminal I had to use pipe for my terminal command. I tried many different commands on my terminal and the last one is :

cat data.txt | ./all-phone-number-filter.sh | cat all-result-phonenumber-filter.txt

But this command doesn’t work, and I don’t know why. So what is the correct command I had to use with this above format please?

I had to use the following format SDTIN | STDOUT for the pipe.

I give you the data.txt file :

[phone]

[phone]

[phone]

[phone]

[phone]

[phone]

[phone]

[phone]

[phone]

[phone]

les numeros suivants ne sont pas valables pour ce programme :

+512 325

+512 251 2545654654

[phone]

+512546546646564646463313

(314) sgf225-2543

[phone]fsgaf

(314afd) 225-2543

FSd(314) 225-2543

The result I need to have is :

  [phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
The number of line is :10 all-result-phonenumber-filter.txt

Answer

A filter will:

• Read from stdin
• Write to stdout

Your program will:

• Read from stdin
• Write to a hard-coded filename

So your program is not a filter and can not be used similarly to what you want.

The easiest/worst way of turning your program into a filter is to write to a temporary file instead, and then cat that:

#!/bin/sh
# TODO: Rewrite to be a nicer filter that doesn't write to files
tmp=$(mktemp)
grep -E '^[ ]{0,9}([0-9]{3}) [0-9]{3}-[0-9]{4}[ ]{0,9}$' $1 | sed 's/^[ t]*//' > "$tmp"
count=$(wc -l < "$tmp")

echo "The number of line is :$count" >> "$tmp"
cat "$tmp"
rm "$tmp"

Now you can treat it as a filter:

$ cat data.txt | ./all-phone-number-filter.sh | tail -n 3
[phone]
[phone]
The number of line is :10

$ cat data.txt | ./all-phone-number-filter.sh > myfile.txt
(no output)

$ nl myfile.txt | tail -n 5
 7  [phone]
 8  [phone]
 9  [phone]
10  [phone]
11  The number of line is :10