Is there an unix command to quote input lines?

I'd offer Perl's quotemeta function. Not quite what you asked, because it escapes spaces rather than replacing them with quotes.

But as a fringe benefit, it also handles other special characters (like *):

perl -nle 'print quotemeta'

(Or as noted in the comments, the shorter form: perl -ple '$_=quotemeta')

Which takes your lines and turns them into:

line\ number\ 1
line\ number\ 2
line\ number\ 3

Which should have the same result - as well as handling:

Line number \"`rm -rf *`\"

And similar such shenanigans :)

Not one specifically designed for it but many multi-purpose tools can do this:

• sed 's/^/"/;s/$/"/'

• perl -pe 's/^/"/;s/$/"/' or perl -lne 'print "\"$_\""'

• awk '{printf "\"%s\"\n",$0}'

• while read -r line; do printf '"%s"\n' "$line"; done

(All of these assume that the line doesn't contain a double quote.)

Note that you'd need to add a " at the beginning and end and transform the "s into "\"":

printf '%s\n' 'foo "bar" baz' 'biz' |
  sed 's/"/"\\""/g;s/^/"/;s/$/"/' |
  xargs printf '<%s>\n'

outputs:

<foo "bar" baz>
<biz>

On GNU system, with shell support $'...':

xargs -d$'\n' printf '%s\n' <<\IN            
line number 1
line number 2
line number 3
IN

With standard tools:

:|paste -d'"' - file - | xargs printf '%s\n'

Both of these assumed that your line didn't contain embedded quotes.

If on a GNU system, look into the --delimiter argument to xargs. Since your input is separated by newlines, you needn't rely on quoting at all, or use any additional tools:

cat files.txt | xargs --delimiter=\\n printf "<%s>"

Where files.txt contains your input:

line number 1
line number 2
line number 3

Gives the output:

<line number 1><line number 2><line number 3>

NB: You do not need to store your input in a file and use cat; you may of course pipe directly from another program. I used cat in my example due to its ubiquity and utility in creating self-contained examples such as this.

Even better (and recommended by the xargs manual) is to have your output program separate the entries by the NUL (\0) instead of a newline, and use the --null option instead of --delimiter, but as long as your input strings will never themselves contain newlines, you're OK with the above approach.

{ echo "x1 x2 x3" ; echo "y1 y2 y3"; } | xargs -L1 echo

x1 x2 x3
y1 y2 y3

The -L1 will use each line separately

However the manpage is spoiling it:

A line ending with a space continues to the next non-empty line.

See here:

{ echo "x1 x2 x3 " ; echo "y1 y2 y3"; } | xargs -L1 echo

x1 x2 x3 y1 y2 y3