How do I use: cat << EOF

Question

I am little confused and not sure, how to add the cat << EOF style to my script. Would really appreciate a little feedback and help.

Here is my script

!/bin/sh
#This is a disk mailer script for hdfs    
DU_RESULTS_HOME=$(sudo -u hdfs hadoop fs -du -s /user/* | sort -r -k 1 -g | awk '{ suffix="KMGT"; for(i=0; $1>1024 && i < length(suffix); i++) $1/=1024; print int($1) substr(suffix, i, 1), $3; }'| head -n 22 |awk '{ print $1"\t\t\t" $2 }')

DF_RESULTS_HOME=$(sudo -u hdfs hadoop fs -df -h /user)
HOSTNAME=$(hostname -s)

MESSAGE_SUBJECT="Disk usage"
MESSAGE_SENDER="xyz"
MESSAGE_EMAIL="abc"

DU_RESULTS_HEADER_USER="Dir size             User"

MESSAGE_BODY="Team:

High level Disk Usage Report for: /user

Please take a moment to clean out any old data, and write temp files to an appropriate filesystem, such as /tmp.

Thanks

if [[ --debug == "$1" ]]; then
    echo debug on 
    printf '%s\n\n\n\n%s\n\n%s\n%s\n\n\n\n\n%s\n%s\n%s' "$MESSAGE_BODY" "$DF_RESULTS_HOME" "$DU_RESULTS_HEADER_USER" "$DU_RESULTS_HOME"
else                 
    echo debug off

    printf '%s\n\n\n\n%s\n\n%s\n%s\n\n\n\n\n%s\n%s\n%s' "$MESSAGE_BODY" "$DF_RESULTS_HOME" "$DU_RESULTS_HEADER_USER" "$DU_RESULTS_HOME" | /bin/mail -s "$MESSAGE_SUBJECT" -r "$MESSAGE_SENDER" "$MESSAGE_EMAIL"                        
fi

Solution

The << is the heredoc. Anything that follows the << acts as the delimiter for the heredoc

cat <<EOF
This is first line
So, this is 2nd
Again, another line
EOF

Enter

So if you would like to store the three lines to a variable do it like below :

from the command line

$ var="$(cat <<EOF
> Bingo
> Gotcha
> Enough
> EOF
> )"

Enter

$ echo "$var" #double quotes are important
Bingo
Gotcha
Enough

from inside the script

#!/bin/bash
var="$(cat <<EOF
Bingo
Gotcha
Enough
EOF
)"
echo "$var"

Comments

[steve]

As it stands, the script needs a quote " after Thanks, to terminate the string.

[ilkkachu]

The << EOF thingy is called a "here document". See here, here and here. I'm not sure what you are asking about those two dozen lines of shell script, so I can't comment on that.

[G-Man Says 'Reinstate Monica']

If you're going to point people to references, please point them to this one.

[Mayur Narang]

so i can do DU_RESULTS_HOME="$(cat <<EOF sudo -u hdfs hadoop fs -du -s /user/* | sort -r -k 1 -g | awk '{ suffix="KMGT"; for(i=0; $1>1024 && i < length(suffix); i++) $1/=1024; print int($1) substr(suffix, i, 1), $3; }'| head -n 22 |awk '{ print $1"\t\t\t" $2 }') sudo -u hdfs hadoop fs -df -h /user EOF )"

[sjsam]

<< is meant for strings like I've demonstrated, not commands. Do you want to execute tall the commands and store the results to DU_RESULTS_HOME?

[Mayur Narang]

no, so in my script i am using so many variables, so i am trying to learn the cat << eof technique to reduce the number of variables.. and probably avoid using print format, which is printf '%s\n\n\n\n%s\n\n%s\n%s\n\n\n\n\n%s\n%s\n%s' "$MESSAGE_BODY" "$DF_RESULTS_HOME" "$DU_RESULTS_HEADER_USER" "$DU_RESULTS_HOME" | /bin/mail -s "$MESSAGE_SUBJECT" -r "$MESSAGE_SENDER" "$MESSAGE_EMAIL"