Delete first line of file if it's empty

Question

How can I delete the first (!) line of a text file if it\'s empty, using e.g. sed or other standard UNIX tools. I tried this command:

sed \'/^$/d\' < somefile         


        

Answer 1

If you don't have to do this in-place, you can use awk and redirect the output into a different file.

awk '{if (NR==1 && NF==0) next};1' somefile

This will print the contents of the file except if it's the first line (NR == 1) and it doesn't contain any data (NF == 0).

NR the current line number,NF the number of fields on a given line separated by blanks/tabs

E.g.,

$ cat -n data.txt
     1  
     2  this is some text
     3  and here
     4  too
     5  
     6  blank above
     7  the end

$ awk '{if (NR==1 && NF==0) next};1' data.txt | cat -n
     1  this is some text
     2  and here
     3  too
     4  
     5  blank above
     6  the end

and

cat -n data2.txt
     1  this is some text
     2  and here
     3  too
     4  
     5  blank above
     6  the end

$ awk '{if (NR==1 && NF==0) next};1' data2.txt | cat -n
     1  this is some text
     2  and here
     3  too
     4  
     5  blank above
     6  the end

Update:

This sed solution should also work for in-place replacement:

sed -i.bak '1{/^$/d}'  somefile

The original file will be saved with a .bak extension