Removing trailing / starting newlines with sed, awk, tr, and friends

Question

I would like to remove all of the empty lines from a file, but only when they are at the end/start of a file (that is, if there are no non-empty lines before them, at the start;

Answer 1

@dogbane has a nice simple answer for removing leading empty lines. Here's a simple awk command which removes just the trailing lines. Use this with @dogbane's sed command to remove both leading and trailing blanks.

awk '{ LINES=LINES $0 "\n"; } /./ { printf "%s", LINES; LINES=""; }'

This is pretty simple in operation.

• Add every line to a buffer as we read it.
• For every line which contains a character, print the contents of the buffer and then clear it.

So the only things that get buffered and never displayed are any trailing blanks.

I used printf instead of print to avoid the automatic addition of a newline, since I'm using newlines to separate the lines in the buffer already.