CODEWITHSUNDEEP
bashawkpipe
Daniel Klöck
Daniel Klöck

Reputation: 21137

give default string as output if command output is empty

I have a command that may have an empty string as output, I want that when I execute:

myCommand | something 'default'

It either returns the output of myCommand or default if the output was empty

I have tried myCommand |awk '{if(\$0==""){print "default"}}' but it doesn't always work.

Upvotes: 5

Views: 4406

Answers (3)

Walter A
Walter A

Reputation: 20002

You can miss empty lines with

myCommand | grep . || echo 'default'

so you might prefer the comment of @BenjaminW. :

var=$(myCommand)
echo "${var:-default}"

Upvotes: 3

Cyrus
Cyrus

Reputation: 88646

echo foo | sed 's/^$/default/'

Output:

foo

echo | sed 's/^$/default/'

Output:

default

Upvotes: 4

cxw
cxw

Reputation: 17041

Since you mentioned awk, here's one way.

Note this is for empty output, i.e., print the default if myCommand outputs nothing at all. If you want to handle a program that outputs a blank line, that's something different.

myCommand | awk -v def="default" '{print} END { if(NR==0) {print def} }'

{print} passes each input line through. At the end (END{...}), NR is the number of input records, i.e., the number of lines received from myCommand. This will be 0 if no output was printed by myCommand. If so, print the value of def, assigned on the command line by -v def="whatever text you want".

Tests:

$ awk -v def="default" '{print} END {if(NR==0) {print def}}' </dev/null
default
$ awk -v def="default" '{print} END {if(NR==0) {print def}}' <<<'foo'
foo

Upvotes: 4

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