mjhjmtu

I'm trying to write a script that uses sed to process lines in a text file to generate sample documentation. I've got most of the script working but I'm stuck with one edge case. Consider the following file

line-1
line-2, part2
line-3-should-be-a-very-long,
 line-3-continued
line-4

The problem is that some, but not all, lines end in a special token (it happens to be a comma). The token indicates that the line should be concatenated with following one to produce one long line.

So in my example line-3-should-be-a-very-long, should be concatenated with line-3-continued to give me line-3-should-be-a-very-long, line-3-continued (I do want to keep the comma). There is no special action on line 2 even though it contains a comma which is NOT at the end of the line.

The rest of the processing is done by piping a few sed and grep commands together, so a sed solution would fit well.

$ sed '/,$/N;s/n//;' file
line-1
line-2
line-3-should-be-a-very-long, line-3-continued
line-4

If the blanks should be deleted:

$ sed '/,$/N;s/n[[:blank:]]*//;' file
line-1
line-2
line-3-should-be-a-very-long,line-3-continued
line-4

(if you want a single space to remain between the lines, replace // in the code by / /)

If lines can be continued multiple times, as in

line-1
line-2
line-3-should-be-a-very-long,
 line-3-continued,
 line-3-continued-further
line-4

then,

$ sed '/,$/:loop;N;s/n[[:blank:]]*//;/,$/bloop;' file
line-1
line-2
line-3-should-be-a-very-long,line-3-continued,line-3-continued-further
line-4

This last sed script explained with annotations:

/,$/ # if the current line ends with a comma, then...
 :loop # define label "loop"
 N # append next line from input (a newline will be inserted in-between)
 s/n[[:blank:]]*// # delete that newline and any blanks (tabs or spaces) directly after it
 /,$/bloop # if the line now ends with comma, branch to the "loop" label

# implicit output of (possibly) modified line at end

sed '/,$/N;s/n[[:blank:]]+/ /' file

When you see a line ending with a comma, read in the next line then replace the newline and leading whitespace of the next line with a single space.