Read lines from File in Bash and parse words into variables for mailx parameters

Question

I have a bash script which reads lines from a text file with 4 columns(no headers). The number of lines can be a maximum of 4 lines or less. The words in each line are separated by SPACE character.

[email protected]   [email protected];[email protected]   Sub1   MailBody1
[email protected]   [email protected];[email protected]   Sub2   MailBody2
[email protected]   [email protected];[email protected]   Sub3   MailBody3
[email protected]   [email protected];[email protected]   Sub4   MailBody4

Currently, I am parsing the file and after getting each line, I am storing each word in every line into a variable and calling mailx four times. Wondering if is there is an elegant awk/sed solution to the below mentioned logic.

• find total number of lines
• while read $line, store each line in a variable
• parse each line as i=( $line1 ), j=( $line2 ) etc
• get values from each line as ${i[0]}, ${i[1]}, ${i[2]} and ${i[3]} etc
• call mailx -s ${i[2]} -t ${i[1]} -r ${i[0]} < ${i[3]}
• parse next line and call mailx
• do this until no more lines or max 4 lines have been reached

Do awk or sed provide an elegant solution to the above iterating/looping logic?

Answer 1

Give this a shot:

head -n 4 mail.txt | while read from to subject body; do
    mailx -s "$subject" -t "$to" -r "$from" <<< "$body"
done

• head -n 4 reads up to four lines from your text file.
• read can read multiple variables from one line, so we can use named variables for readability.
• <<< is probably what you want for the redirection, rather than <. Probably.

Answer 2

The above while loop works well as a simple alternative to sed and awk if you have a lot of control over how to display the lines of text in a file. the read command can use a specified delimiter as well, using the -d flag.

Another simple example:

I had used mysql to grab a list of users and hosts, putting it into a file /tmp/userlist with text as shown:

user1 host1
user2 host2
user3 host3

I passed these variables into a mysql command to get grant info for these users and hosts and append to /tmp/grantlist:

cat /tmp/userlist | while read user hostname;
do
  echo -e "\n\nGrabbing user $user for host $hostname..."
  mysql -u root -h "localhost" -e "SHOW GRANTS FOR '$user'@$hostname" >> /tmp/grantlist
done