Exit for loop when a condition is met, for an array

Question

I am working on a script.

The script runs on multiple servers.
It sends an email to the address mentioned in the TO field.
There can be one of the 2 recipients of the mail ([email protected] or [email protected]), depending on the server on which the script is executing.
There's a list of 4 pre-defined servers. If the script is executing on one of these servers, it sends the email to [email protected]. Else, it sends the email to [email protected].

I thought this is correct, but I missed a logic that on every server both if and else condition will be checked.

#!/bin/bash
set -x
SERVER_NAME=$(hostname -s)
FILE_TEMP=/tmp/new.log
echo -e "This is a test from SERVER_NAME" >> $FILE_TEMP
subject="sending file from $SERVER_NAME"

Servers=(flipunix1 flipunix2 flipunix3 flipunix7)
for i in ${Servers[*]}
do
    if [ "$SERVER_NAME" == "$i" ];
    then
        to="[email protected]"
        echo -e "server name picked is $SERVER_NAME and i value is $i "
        break
    else
        to="[email protected]"
        echo -e "server name picked is $SERVER_NAME and i value is $i "
        break
    fi
done

also_to="[email protected]"
mail -s "$subject" "$to" "$also_to" < $FILE_TEMP

David C. Rankin · Accepted Answer · 2020-09-05 02:16:59Z

1

It looks like you want to send to="[email protected]" if the SERVER_NAME is one within the Servers array, and if it isn't, you want to send to="[email protected]". If so, your loop logic sets to="[email protected]" and breaks the loop every time SERVER_NAME does not match -- even if SERVER_NAME may match on the next iteration. You can remedy that by removing the break, e.g.

for i in ${Servers[*]}
do
    if [ "$SERVER_NAME" = "$i" ];
    then
        to="[email protected]"
        echo -e "server name picked is $SERVER_NAME and i value is $i "
        break
    else
        to="[email protected]"
    fi
done

Now to="[email protected]" is set each time, but if the name is found in SERVER_NAME the loop exits with to="[email protected]". Only if there is no match doe the send remain to="[email protected]".

You can simply set to="[email protected]" before the loop and do:

#!/bin/bash
set -x
SERVER_NAME=$(hostname -s)
FILE_TEMP=/tmp/new.log
echo -e "This is a test from SERVER_NAME" >> $FILE_TEMP
subject="sending file from $SERVER_NAME"
to="[email protected]"

Servers=(flipunix1 flipunix2 flipunix3 flipunix7)
for i in ${Servers[*]}
do
    if [ "$SERVER_NAME" = "$i" ];
    then
        to="[email protected]"
        echo -e "server name picked is $SERVER_NAME and i value is $i "
        break
    fi
done

also_to="[email protected]"
mail -s "$subject" "$to" "$also_to" < $FILE_TEMP

That will accomplish the same thing. (you can add an if ... fi and check if [ "$to" = "[email protected]" ] if you want to output a message that that was used.)

You can also eliminate the loop entirely and simply use [[ ... ]] with the array contents and SERVER_NAME, e.g.

#!/bin/bash
set -x
SERVER_NAME=$(hostname -s)
FILE_TEMP=/tmp/new.log
echo -e "This is a test from SERVER_NAME" >> $FILE_TEMP
subject="sending file from $SERVER_NAME"
to="[email protected]"

Servers=(flipunix1 flipunix2 flipunix3 flipunix7)

[[ ${Servers[@]} =~ $SERVER_NAME ]] && {
    to="[email protected]"
    echo -e "server name picked is $SERVER_NAME "
}

also_to="[email protected]"
mail -s "$subject" "$to" "$also_to" < $FILE_TEMP

(same note on checking if [ "$to" = "[email protected]" ] if you want to output something based on that being chosen)

Let me know if I didn't understand correctly.

(note: there is only one = to check string equality in [...])

edited Sep 5, 2020 at 2:16

answered Sep 5, 2020 at 1:52

David C. Rankin

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3 Comments

Erroruploading Over a year ago

This is such a nice logic i missed it , surprisingly i used almost same logic few months ago on a script. But thank you, you showed the simplicity.

Erroruploading Over a year ago

Sure, I gonna do that. I have still some doubts on the answers, once I have them,I will make sure to mark as answered.

David C. Rankin Over a year ago

Okay, that is fine. Generally a day or so is the normal active lifetime for a question. If you edit it will move it back active. Take as long as you like.

Rfroes87 · Accepted Answer · 2020-09-05 02:29:12Z

0

You could try this:

#!/bin/bash
set -x
SERVER_NAME=$(hostname -s)
FILE_TEMP=/tmp/new.log
echo -e "This is a test from SERVER_NAME" >> $FILE_TEMP
subject="sending file from $SERVER_NAME"

Servers=(flipunix1 flipunix2 flipunix3 flipunix7)
for i in ${Servers[*]}
do
if [ "$SERVER_NAME" == "$i" ];
then
to="[email protected]"
echo -e "server name picked is $SERVER_NAME and i value is $i "
break
fi
done

if [ -z "$to" ];
then
to="[email protected]"
echo -e "server name picked is $SERVER_NAME "
fi

also_to="[email protected]"
mail -s "$subject" "$to" "$also_to" < $FILE_TEMP

or (a shorter version)

#!/bin/bash
set -x
SERVER_NAME=$(hostname -s)
FILE_TEMP=/tmp/new.log
echo -e "This is a test from SERVER_NAME" >> $FILE_TEMP
subject="sending file from $SERVER_NAME"

Servers=(flipunix1 flipunix2 flipunix3 flipunix7)

if ! printf "%s\n" "${Servers[@]}" | grep -qw -m 1 "$SERVER_NAME";
then
to="[email protected]"
else
to="[email protected]"
fi

also_to="[email protected]"
mail -s "$subject" "$to" "$also_to" < $FILE_TEMP

edited Sep 5, 2020 at 2:29

answered Sep 5, 2020 at 1:56

Rfroes87

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6 Comments

Erroruploading Over a year ago

if ! printf "%s\n" "${Servers[@]}" | grep -qw -m 1 "$SERVER_NAME"; thank you for the response. Could you help me understand the logic here? Would really help me in understand better.

Rfroes87 Over a year ago

Of course! First, I'm printing all the elements in the Servers array, putting them into separate lines (printf "%s\n" "${Servers[@]}"); with the grep command, we filter by the exact (-w option) first match (-m 1) and suppress the output to stdout (-q). The if statement is a stylized approach to running the command described above in a previous line and constructing the condition as if [ $? != 0 ]; then; it's just the syntax shellcheck recommended by the SC2181 standard. If you have any more questions, let me know!

M. Nejat Aydin Over a year ago

The -m 1 option isn't necessary since the -q causes the grep to exit immediately when a match is found.

Erroruploading Over a year ago

@Rfroes87 thanks for the explanation, the latter one is beneficial to me. And as @M. Nejat Aydin suggested, I have removed -m 1 and see no difference. Any recommendations on it?

Erroruploading Over a year ago

@Rfroes87 I am also thinking, if I want to keep all the servers names in a file on same directory ( say servers_info.txt) , can i read them like below and same works? I am getting error currently .

if ! echo -e servers_info.txt | grep -qw -m 1 "$SERVER_NAME"; then to="[email protected]" else to="[email protected]" fi

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