How can I replace a newline with its escape sequence?

Using sed to make text that contains certain characters suitable for use in string literals is straightforward:

sed "s/\\\\/\\\\\\\\/g"
sed "s/\\\"/\\\\\\\"/g"

But how can I do something similar with a text file containing newline characters?

1

7 Answers

If you're dealing with a pipelined command, then I like @vossad01's answer. However, in a multi-line script, I prefer normal Bash parameter expansion, which is both more efficient (doesn't need to fork a new process for sed or create any pipes) and perhaps a bit easier to read:

${varName//$'\n'/\\n}

Reader's guide:

• ${...} - Interpret the internal stuff using parameter expansion
• varName - Name of the variable containing the content
• // - Replace all instances of...
• $'\n' - The literal newline character (we're turning the escape into the literal here)
• / - Replace with...
• \\n - The newline escape sequence ("\n"): note that we had to escape the backslash itself

Example:

$ foo="$(printf '%s\n' $(seq 1 3))"
$ echo "$foo"
1
2
3
$ echo "${foo//$'\n'/\\n}"
1\n2\n3

Use:

sed ':a;N;$!ba;s/\n/\\n/g'

Which uses the answer from How can I replace a newline (\n) using sed? substituting an escaped newline character as the replacement to match the question here.

1

I solved this one with:

sed 's/$/\\n/g' | tr -d'\n'

sed puts '\\n' at the end of every line, then tr removes the newlines.

1

sed is line based, and this can cause issues when trying to replace newline characters.

the official documentation for sed makes a specific reference to newline characters and states they are stripped off before being passed to sed.

I would suggest that 'tr' would probably be a better fit here.

as an example, to replace newline characters with spaces:

tr '\n' ' ' < inputfile

6

I'd like to extend David Moytan's solution:

cat /etc/passwd | perl -e 'while(<>) { $_ =~ s/[\r\n]/__NEWLINE__/g; print "$_" }'

I had this problem too.

You can use the \a function to start every newline with the proper escape sequence, then pipe the resulting function into echo -n which suppresses newlines.

echo -n $(sed '\a
\\n');

Stick whatever you're sed-ing in the parentheses before the sed command.

This awk solution worked for me:

$ awk 1 ORS='\\n' file.txt

Credit goes to this excellent answer.

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