SED - insert a blank line after every input line that consists of capital letters and spaces - linux

Question

I have a text file and I need a command using sed to insert a blank line after every line that that consists of capital letters and spaces only.

Answer 1

This might work for you (GNU sed):
sed '/^[[:blank:][:upper:]][[:blank:][:upper:]]*$/G' file
This appends the hold space (by default it contains a newline) to lines containing at least one or more whitespace or uppercase characters.

Answer 2

Given:
$ cat file
LINE LINE LINE
Line Line Line
Line 1
LINE 2
END!
====
You can use s/// to add a \n to the line:
With POSIX sed, use a literal new line in the sed script:
$ sed 's/^\([[:upper:][:blank:]]*\)$/\1\
/' file
LINE LINE LINE
Line Line Line
Line 1
LINE 2
END!
====
With GNU sed, you can use the representation of \n:
$ sed 's/^\([[:upper:][:blank:]]*\)$/\1\n/' file
You can also use a\ to append in sed. I have tried to get sed append to work but cannot reliably with POSIX, BSD and GNU sed since POSIX and BSD do not support \n
With GNU sed (note space after a\):
$ sed '/^[[:upper:][:blank:]]*$/a\ ' file
BSD:
$ sed '/^[[:upper:][:blank:]]*$/a\
\
' file
Those are not exactly equivalent since the GNU version has a space on the blank line.
The version of POSIX sed I have did not work with either of those...
Given the platform and version differences of sed, you might consider awk to do this since simple awk's are easier to make universal.
This works on every awk I have:
$ awk '1; /^[[:upper:][:blank:]]*$/{print ""}' file
With awk you can also make it so that blank lines are not doubled by making sure there is at least non blank like so:
$ awk '1; /^[[:upper:][:blank:]]+$/ && NF>1 {print ""}' file

Answer 3

Sure. Just insert lines with a:
sed '/^[[:blank:]A-Z]*$/a\'
The a command inserts the string after it after every matching line (end the string with a backslash). So the above command just inserts an empty line after all lines that contains solely of capital letters and spaces. That's exactly what you want.