Extracting string to variable using regex bash

Question

I have a string which is like:

Received-SPF: pass (fake.link.com: Sender is authorized to use '[email protected]' in 'mfrom' identity (mechanism 'include:spf.smtp2go.com' matched)) receiver=pmxlab01.permission.email; identity=mailfrom; envelope-from="[email protected]"; helo=e2i353.smtp2go.com; client-ip=103.2.141.97
MIME-Version: 1.0
From: [email protected]
To: [email protected]
Date: 24 Aug 2021 14:46:30 +0100
Subject: Test Email 2xM9e5Dj
Content-Type: multipart/alternative;
 boundary=--boundary_11_ddba370a-13e2-4ffc-8b36-0eb7a5cde80e
Message-Id: <[email protected]>
Feedback-ID: 575655m:575655aVI_MaS:575655sNpPp5WOdD


----boundary_11_ddba370a-13e2-4ffc-8b36-0eb7a5cde80e
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: quoted-printable

This is a text message
----boundary_11_ddba370a-13e2-4ffc-8b36-0eb7a5cde80e
Content-Type: text/html; charset=us-ascii
Content-Transfer-Encoding: quoted-printable

This is a html message
----boundary_11_ddba370a-13e2-4ffc-8b36-0eb7a5cde80e--

This is stored in a variable called $emailText

I'm trying to use a regex to take the From part out of the text

From: [email protected]

My regex isnt super strong, however my testing looks like this works: (?<=From: ).*.

But when I try and take the text out, it appears I can't get the regex to go through properly.

echo [[ $emailText =~ (?<=From: ).*. ]]

bash regex doesn't support lookbehind or lookahead assertions. — anubhava
– anubhava, Commented Aug 24, 2021 at 14:36
You want to use a language with a proper email parsing library, like Python. Getting the literal value of the header is just the first step an any meaningful email processing. — tripleee
– tripleee, Commented Aug 24, 2021 at 14:46
Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems. :-). — Ed Morton
– Ed Morton, Commented Aug 24, 2021 at 18:32

anubhava · Accepted Answer · 2021-08-24 16:17:41Z

5

bash regex doesn't support lookbehind or lookahead assertions.

It is much easier to use a non-regex approach using awk here:

awk -F ': ' '$1 == "From" {print $2}' <<< "$emailText"

[email protected]

edited Aug 24, 2021 at 16:17

answered Aug 24, 2021 at 14:37

anubhava

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4 Comments

MissCoder87 Over a year ago

Thanks for this, I could be putting it in wrong, but i'm getting the following error ./test.sh: 27: Syntax error: redirection unexpected

Arkadiusz Drabczyk Over a year ago

@MissCoder87: you're not using Bash

anubhava Over a year ago

@MissCoder87: If not using bash then use: echo "$emailText" | awk '$1 == "From:" {print $2}'

MissCoder87 Over a year ago

I see, thank you - i've updated to /bin/bash and it's working perfect thank you

Cyrus · Accepted Answer · 2021-08-24 18:17:59Z

3

With bash:

[[ "$emailText" =~ From:\ ([^$'\n']*) ]] && echo "${BASH_REMATCH[1]}"

Output:

[email protected]

answered Aug 24, 2021 at 18:17

Cyrus

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Comments

RavinderSingh13 · Accepted Answer · 2021-08-25 16:30:00Z

3

With your shown samples, attempts; please try following awk code. Simple explanation would be, checking condition if 1st field is From: then print 2nd field of that line.

awk '$1=="From:"{print $2}' Input_file

2nd solution: In case you have only 1 entry of From: in whole file then try following, where we can use exit function to exit from Input_file after printing the matched line, to stop un-necessary reading of whole Input_file.

awk '$1=="From:"{print $2;exit}' Input_file

answered Aug 25, 2021 at 16:30

RavinderSingh13

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Comments

tripleee · Accepted Answer · 2021-08-24 14:59:03Z

2

Assuming you only want the email terminus, here's a quick and dirty Awk script.

awk '/^$/ { exit 1 }
    /^From: .* <[^<>@]+@[^<>]+>/ {
        split($0, g, /[<>]/); print g[1]; exit }
    /^From: / { print $2; exit }' file.eml

This should work correctly for all these cases:

From: Real Name <[email protected]>
From: "Name, Real" <[email protected]>
From: [email protected]
From: [email protected] (Real Name)
From: =?q?utf-8?Real_N=A3=E4me?= <[email protected]>

As especially the last example should convince you, you will need significantly more work if you also need the full name of the correspondent in normalized form.

answered Aug 24, 2021 at 14:59

tripleee

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Comments

The fourth bird · Accepted Answer · 2021-08-24 15:36:20Z

2

If there should be a mail address present, you can match it first using awk (without the unsupported need for lookarounds)

awk 'match($0, /^From: [^[:space:]@]+@[^[:space:]@]+$/) {
  print $2
}' <<< "$emailText"

Output

[email protected]

edited Aug 24, 2021 at 15:36

answered Aug 24, 2021 at 14:41

The fourth bird

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2 Comments

tripleee Over a year ago

This is only correct for From: fields where the terminus alone is present. Most real-world email looks like From: Real Name <[email protected]> (or, heavens, From: "Victim, Microsoft" <[email protected]>)

The fourth bird Over a year ago

@tripleee Fair point, if that is the case that printing the second field by default is not guaranteed to work and we need a more sophisticated approach.

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