Shell – Using sed to convert newlines into spaces

sedshell

Say I have a shell variable $string that holds some text with several newlines, e.g.:

string="this
is 
a test"

I would like to convert this string into a new string new_string where all line breaks are converted into spaces:

new_string="this is a test"

I tried:

print $string | sed 's/\n/ /g'

but it didn't work

I'm also wondering if there is a way of doing this using perl -0777 's/\n/ /g' or maybe the command tr ?

Best Answer

If you only want to remove the new lines in the string, you don't need to use sed. You can use just

$  echo "$string" | tr '\n' ' '

as others had pointed.

But if you want to convert new lines into spaces on a file using sed, then you can use:

$ sed -i ':a;N;$!ba;s/\n/\t/g' file_with_line_breaks

or even awk:

$ awk '$1=$1' ORS=' ' file_with_line_breaks > new_file_with_spaces

Related Solutions

How to strip multiple spaces to one using sed

The use of grep is redundant, sed can do the same. The problem is in the use of * that match also 0 spaces, you have to use \+ instead:

iostat | sed -n '/hdisk1/s/ \+/ /gp'

If your sed do not supports \+ metachar, then do

iostat | sed -n '/hdisk1/s/  */ /gp'

Shell – Write variable containing large text with \n to a file with common shell interpreters. How to do it

You can make a here document and use cat:

$ cat <<EOT >output
$a
EOT
$ wc -l output
40000

I don't know exactly how powerful your Busybox's ash is (it's configurable), but that should work anywhere, even with no builtins at all. It expands the variable value into a quasi-file, which is then given to cat, rather than putting the value itself into the command line.

Since you seem to have literal "\n" in your string that you want to get rid of, you can also use string replacement during parameter subsitution. This can be configured out of Busybox's ash, in which case you'll have to go to sed. If you do have this (non-POSIX) extension, you can use ${var//\\\n/$NEWLINE}:

$ busybox ash
$ foo="x\ny\nz"
$ echo "$foo"
x\ny\nz
$ NEWLINE="
"
$ echo "${foo//\\\n/$NEWLINE}"
x
y
z

This is the same syntax as Bash; ${var/pattern/replacement}, where pattern is global if it starts with /. It seems your ash has a lot configured out of it, so this might not be there at all. In that case you're probably going to have to go with sed, although I guess judicious use of IFS and read would let you work around that and reconstruct a correct string.

Best Answer

Related Solutions

How to strip multiple spaces to one using sed

Shell – Write variable containing large text with \n to a file with common shell interpreters. How to do it

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