awk issue selecting lines between two patterns

Question

"Issue"... The command is doing what is actually instructed to.

Given this mbox format file:

From: [email protected] #identifies the beginning of the first mail    
...
Subject: crcheck.sh #identifies the beginning of the mail body
...
MYVARIABLE="123"
...
From: [email protected] #identifies the beginning of the next mail
...
Subject: crcheck.sh #identifies the beginning of the mail body
...
From: [email protected] #identifies the beginning of next mail
...
Subject: crcheck.sh #identifies the beginning of the mail body
EVILVARIABLE="0.00" #just to mention a value that would cause division by zero errors and crash my main script.
...
From: [email protected] #identifies the beginning of the next mail
...

I need to select all lines between a valid Subject: and the next From:, but the From: preceiding the Subject line should be the $GOODSENDER one.

The code I'm running:

GOODSUBJECT="crcheck.sh"
GOODSENDER="[email protected]"
cat $MBOX |awk "/Subject\: $GOODSUBJECT$/{a=1}/From\:\ $GOODSENDER /{print;a=0}a"|grep $i\=\"

Outputs:

MYVARIABLE="123"
EVILVARIABLE="0.00"

Expected output:

MYVARIABLE="123"

The command is doing what it's instructed to, as those lines are acutally between two of the lines I set as patterns for awk.

But how can I adjust it to have this desidered behaviour?

Answer 1

Try:

$ awk "/Subject:/{a=0} /From:/{a=0; b=0} a && b && /MYVARIABLE=/{print} /Subject: crcheck.sh$/{a=1} /From: [email protected]/{b=1}" mbox
MYVARIABLE="123"

How it works

• /Subject:/{a=0} /From:/{a=0; b=0}

  When we reach a subject or from line, turn all flags false.

• a && b && /MYVARIABLE=/{print}

  If both flags are true and the line includes the string MYVARIABLE=, then print the line.

• /Subject: crcheck.sh$/{a=1}

  If the subject line is good, set flag a to true.

• /From: [email protected]/{b=1}

  If the from line is good, set flag b to true.

Notes

1. It is poor practice to use all caps for shell variables. The system use all caps for its variables and you don't want to accidentally overwrite one of them.

2. cat is unneeded. Awk takes file names as arguments.

3. In regexes, : and space are not special. They don't need to be escaped.

4. In email headers, Subject: and From: are both supposed to start at the beginning of the line. A better regex for each might be /^Subject:/ and /^From:/ where ^ is the regex symbol for start-of-line.

Passing a variable to awk

$ var=MYVARIABLE
$ awk -v x="$var" '/Subject:/{a=0} /From:/{a=0; b=0} a && b && $0 ~ (x"="){print} /Subject: crcheck.sh$/{a=1} /From: [email protected]/{b=1}' mbox
MYVARIABLE="123"

Sample Input

The output above was generated using this as the input file:

$ cat mbox
From: [email protected]
...
Subject: crcheck.sh
...
MYVARIABLE="123"
...
From: [email protected]
...
Subject: crcheck.sh
...
From: [email protected]
...
Subject: crcheck.sh
EVILVARIABLE="0.00"
...
From: [email protected]
...

This is the same as in the question except that, to restore it to mbox format, the added comments have been removed.