4.1. How do I insert a newline into the RHS of a substitution?
Several versions of sed permit '\n' to be typed directly into the
RHS, which is then converted to a newline on output: ssed,
gsed302a+, gsed103 (with the -x switch), sed15+, sedmod, and
UnixDOS sed. The easiest solution is to use one of these
versions.
For other versions of sed, try one of the following:
(a) If typing the sed script from a Bourne shell, use one backslash
"\" if the script uses 'single quotes' or two backslashes "\\" if
the script requires "double quotes". In the example below, note
that the leading '>' on the 2nd line is generated by the shell to
prompt the user for more input. The user types in slash,
single-quote, and then ENTER to terminate the command:
[sh-prompt]$ echo twolines | sed 's/two/& new\
>/'
two new
lines
[bash-prompt]$
(b) Use a script file with one backslash '\' in the script,
immediately followed by a newline. This will embed a newline into
the "replace" portion. Example:
sed -f newline.sed files
# newline.sed
s/twolines/two new\
lines/g
Some versions of sed may not need the trailing backslash. If so,
remove it.
(c) Insert an unused character and pipe the output through tr:
echo twolines | sed 's/two/& new=/' | tr "=" "\n" # produces
two new
lines
(d) Use the "G" command:
G appends a newline, plus the contents of the hold space to the end
of the pattern space. If the hold space is empty, a newline is
appended anyway. The newline is stored in the pattern space as "\n"
where it can be addressed by grouping "\(...\)" and moved in the
RHS. Thus, to change the "twolines" example used earlier, the
following script will work:
sed '/twolines/{G;s/\(two\)\(lines\)\(\n\)/\1\3\2/;}'
(e) Inserting full lines, not breaking lines up:
If one is not changing lines but only inserting complete lines
before or after a pattern, the procedure is much easier. Use the
"i" (insert) or "a" (append) command, making the alterations by an
external script. To insert "This line is new" BEFORE each line
matching a regex:
/RE/i This line is new # HHsed, sedmod, gsed 3.02a
/RE/{x;s/$/This line is new/;G;} # other seds
The two examples above are intended as "one-line" commands entered
from the console. If using a sed script, "i\" immediately followed
by a literal newline will work on all versions of sed. Furthermore,
the command "s/$/This line is new/" will only work if the hold
space is already empty (which it is by default).
To append "This line is new" AFTER each line matching a regex:
/RE/a This line is new # HHsed, sedmod, gsed 3.02a
/RE/{G;s/$/This line is new/;} # other seds
To append 2 blank lines after each line matching a regex:
/RE/{G;G;} # assumes the hold space is empty
To replace each line matching a regex with 5 blank lines:
/RE/{s/.*//;G;G;G;G;} # assumes the hold space is empty
(f) Use the "y///" command if possible:
On some Unix versions of sed (not GNU sed!), though the s///
command won't accept '\n' in the RHS, the y/// command does. If
your Unix sed supports it, a newline after "aaa" can be inserted
this way (which is not portable to GNU sed or other seds):
s/aaa/&~/; y/~/\n/; # assuming no other '~' is on the line!
