How to append a value to the output after using sed command?

Shell Programming and Scripting
1

Hi All,

I have a file where I am converting newlines to comma separated values but I would like to append zero if the output is empty

Here is the command I am using

sed -n -e 'H;${x;s/\n/,/g;s/^,//;p;}' test1.txt

test1.txt will have comma seperated values but sometimes this file can be empty so I wanted to append 0 to this file how could I do this.

I appreciate your help.

Regards,
raj

2

I am not clear what you are asking, but maybe this will be helpful to you:
bash has -s test for non-empty files,

if [ ! -s empty_file ]; then echo "EMPTY"; else echo "Not Empty"; fi

So you could do

echo "0" > empty_file

if the file is empty.

3

I wanted to do like this echo "0" >> sed command please let me know if this works and output file should have 0 in it. how do i do this approach

Regards,
raj

4

What @Migurus told is the easiest way!

5

Another approach using awk:

awk 'NF{s = s ? s OFS $0 : $0; f = 1 }END{ if (f) print s; else print "0" }' OFS=, test1.txt
6

Hi Yoda,

I tried using awk command but its just showing as 0 at unix command prompt but not appended to the file

awk 'NF{s = s ? s OFS $0 : $0; f = 1 }END{ if (f) print s; else print "0" }' OFS=, test1.txt

Please let me know if I am wrong somewhere

Thanks
Raj

7

Me too, I'm not clear what you want to achieve. Do you want the original file to contain a single "0" char after the operation if before it is empty?