CODEWITHSUNDEEP
bashawk
Numpty
Numpty

Reputation: 1481

Bash: If file exists, read line, do this *then* than, then continue to next line

Straight to the point: I need to do the following (psuedo-code):

if [ -f <file_that_exists> ]

then

while read
do


awk '{print "do stuff for " $1}' THEN immediately below it awk '{print "do stuff for" $2}'
Then continue to next line

The file I'm trying to parse has two columns (host pairs if you will):

host_1     host_2
host_3     host_4

What I need the output to look like is the following:

Do stuff for host_1
Do stuff for host_2
Do stuff for host_3
Do stuff for host_4

What I'm trying now looks like:

Do stuff for host_1
Do stuff for host_3
Do stuff for host_5
Do stuff for host_7
then
Do stuff for host_2
Do stuff for host_4
Do stuff for host_6
Do stuff for host_8

I'm not sure if I'm being very clear, so if you need further clarification please let me know.

Thanks!

Upvotes: 0

Views: 243

Answers (2)

glenn jackman
glenn jackman

Reputation: 246774

This is a case where you want to use a for-loop to iterate over the words in your file:

for host in $(< filename); then
    Do something with $host
done

or, read 2 words from each line

while read host_a host_b; do
    Do something with $host_a
    Do something with $host_b
done < filename

Upvotes: 0

Dan Fego
Dan Fego

Reputation: 13994

I believe what you're aiming for can be done in a single awk statement:

awk '{ print "Do stuff for " $1; print "Do stuff for " $2 }' filename

Or alternatively:

awk '{ printf "Do stuff for %s\nDo stuff for %s\n", $1, $2 }' filename

No need to use the shell to read from the file; just pass the file name to awk directly. The key to the above solution is that awk will read from the file, record by record (here: line by line), and have each field (here: host_1, host_2, etc.) in that line be encoded as $1 and $2. If you had a variable number of fields in each line, the solution would be a bit different (possibly involving a loop within awk) but the above is the simple case.

Upvotes: 3

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