Question

On Linux (BusyBox, QNAP-NAS) I want to add some extra path to my .bashrc file via script using sed. The relevant part of the file looks as follows:

[...]
export PATH=\
/bin:\
/sbin:\
/usr/bin:\
/usr/sbin:\
/usr/local/bin
[...]

The extra line to be inserted (at position 4 in the original file) is /opt/bin:/opt/sbin:\. To get this done my sed one-liner looks like this:

sed '4i/opt/bin:/opt/sbin:\\' .bashrc > .bashrc.tmp

, correctly escaping the trailing backslash. Somehow sed converts the remaining \' into a newline eating up the trailing backslash, resulting in:

[...]
export PATH=\
/opt/bin:/opt/sbin:

/bin:\
[...]

Adding a third backslash gives me the trailing backslash, but still adds the newline, so

sed '4i/opt/bin:/opt/sbin:\\\' .bashrc > .bashrc.tmp

results into

export PATH=\
/opt/bin:/opt/sbin:\

/bin:\

If I add an extra space in my sed command

sed '4i/opt/bin:/opt/sbin:\\ ' .bashrc > .bashrc.tmp

everything looks fine, but I get the extra space at the end of line as well.

export PATH=\
/opt/bin:/opt/sbin:\  # extra space here

/bin:\

What did the trick for now is a second sed command removing the trailing spaces

#!/bin/sh

sed -e '4i/opt/bin:/opt/sbin:\\ ' .bashrc > .bashrc.tmp
sed -e 's/[ \t]*$//' .bashrc.tmp > .bashrc.tmp2  # change \t to real tab

But still I wonder why sed is transforming \' into a newline, and how to solve the above job with a simple one-liner? How can I insert (or append) a line with a trailing backslash using sed?
Thanks in advance.

Answer 1

Here’s a workaround:

sed '4s|^|/opt/bin:/opt/sbin:\\\n|' .bashrc