sed (in bash) works with [ \t] but not with \s?

Question

I want to search-replace something containing whitespace on a bash command line, and I assumed sed would be the easiest way to go.

Using [ \t] denoting either tab or space, to match the whitespace, works as intended:

echo "abc xyz" | sed "s/[ \t]xyz/123/"
abc123

But using \s instead of [ \t] does not, to my surprise:

echo "abc xyz" | sed "s/\sxyz/123/"
abc xyz

I'm fairly new to bash so I might be missing something trivial, but no matter what I do, I can't get this to work. Using \\s instead of \s, using single quotes (' instead of "), putting the whitespace marker inside square brackets (like [\s] or even [\\s]), nothing seems to help..?

(edit) in case it differs from one sed / bash version to another: I'm working on OS X here.

Additionally, I noticed that when I add a + after the [ \t] whitespace part, to optionally grab multiple space/tab characters if present, it doesn't work anymore either...??

echo "abc xyz" | sed "s/[ \t]+xyz/123/"
abc xyz

(and again, also tried with \+ instead of +, and single quotes instead of double quotes, nothing helps)

Myxomycete

Interesting and related: How to match whitespace in sed?. Basically, For POSIX compliance, use the character class [[:space:]] instead of \s, since the latter is a GNU sed extension So you are probably working in a non-GNU sed. Could you provide the output of sed --version? – Pompeii

on sed here, it works as expected; as @Pompeii suggest, it is gnu sed indeed – Excursion

have you thoroughly read the sed man page on your system? It should document what does and does not work. Type man sed at a command prompt. – Trovillion

Ah, thanks, sed --version says illegal option -- - so I guess it's not GNU :) – Myxomycete

Answer 1

As seen in SuperUser's How to match whitespace in sed?:

For POSIX compliance, use the character class [[:space:]] instead of \s, since the latter is a GNU sed extension

So you are probably running a non-GNU sed version, hence \s not working to you.

You have two solutions:

• To use (space) and \t together, like you were doing.
• To use [[:space:]].

Pompeii

Confirmed, thanks, it works with [[:space:]] However, the + modifer still doesn't work, any ideas? Note that [[:space:]]\{1,999\} does work, but [[:space:]]+ or [[:space:]]\+ do not. – Myxomycete

To use + normally you need either to escape it: \+ or to use -r for extended regex: sed -r "s/[[:space:]]+/X/" – Pompeii

@Myxomycete the POSIX-compliant syntax for one or more matches Is \{1,\} - anything else is an extension. – Caldarium

@TomFenech that is no longer true. the most recent spec defines + when using sed -E (not -r) flag. It even specifies reluctant operators (+?, *?, ??) – Siana

Answer 2

echo 'abc xyz<>abcxyz' | sed 's/[[:space:]]xyz/123/g'
abc123<>abcxyz
echo 'abc xyz<>abcxyz' | sed "s/[[:space:]]xyz/123/g"
abc123<>abcxyz

doesn't work on very old sed version but fine on GNU sed as posix complaint (AIX, ...)

Vera