sed command to replace multiple spaces into single spaces

Question

I tried to replace multiple spaces in a file to single space using sed.

But it splits each and every character like below. Please let me know what the problem is ...

$ cat test.txt
 iiHi Hello   Hi
this   is   loga

$

$ cat test.txt | tr [A-Z] [a-z]|sed -e "s/ */ /g"
 i i h i h e l l o h i
 t h i s i s l o g a

Possible duplicate of [How to remove extra spaces in bash?](https://stackoverflow.com/q/13092360/608639) — jww, May 26 '19 at 22:46

score 28 · Accepted Answer · answered Apr 08 '14 at 14:02

28

Your sed command does the wrong thing because it's matching on "zero or more spaces" which of course happens between each pair of characters! Instead of s/ */ /g you want s/ */ /g or s/ +/ /g.

answered Apr 08 '14 at 14:02

John Zwinck

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just for clarify, space must be scaped, so it is: `s/\ \ */\ /g` or `s/\ +/\ /g` – Iván Rodríguez Torres Mar 04 '17 at 02:22
Only if the argument to sed isn't surrounded by quotes – Gijs Oct 15 '20 at 11:21

score 24 · Answer 2 · answered Apr 08 '14 at 14:48

24

Using tr, the -s option will squeeze consecutive chars to a single one:

tr -s '[:space:]' < test.txt

 iiHi Hello Hi
this is loga

To downcase as well: tr -s '[:space:]' < test.txt | tr '[:upper:]' '[:lower:]'

answered Apr 08 '14 at 14:48

glenn jackman

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This should have been more upvoted! Never heard of this utility. – Evan Zamir Feb 19 '16 at 00:05

Amos Baker · Answer 3 · 2020-07-30T19:33:38.647

12

sed 's/ \+/ /g' test.txt | tr [A-Z] [a-z]

or

sed 's/\s\+/ /g' test.txt | tr [A-Z] [a-z]

Good grief that was terse, because * matches zero or more it inserted a space after every character, you want + which matches one or more. Also I switched the order because in doing so you don't have to cat the file.

edited Jul 30 '20 at 19:33

answered Dec 04 '15 at 18:08

Amos Baker

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sed must be with '-r', otherwise regexps would not work `sed -r 's/\s\+/ /g' test.txt` – Temak Nov 23 '20 at 17:00
@Temak - that must be dependent on the flavor of sed, with GNU sed 4.4 I did not need the flag. – Amos Baker Dec 16 '20 at 21:03
`$ man sed | grep s\/reg -A1 s/regexp/replacement/ Attempt to match regexp against the pattern space. If successful, replace that portion matched with replacement. The replacement may contain the special character & to` – Amos Baker Jun 22 '22 at 20:57

score 3 · Answer 4 · answered Apr 08 '14 at 15:02

3

You can use awk to solve this:

awk '{$0=tolower($0);$1=$1}1' test.txt
iihi hello hi
this is loga

answered Apr 08 '14 at 15:02

Jotne

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score 0 · Answer 5 · answered Apr 08 '14 at 14:00

0

Maybe you can match the following regex for multiple spaces:

'\s+'

and replace with just one space as follows:

' '

answered Apr 08 '14 at 14:00

sshashank124

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This needs the `-E`-flag for extended regexes. – FelixJN Jun 24 '21 at 20:19

sed command to replace multiple spaces into single spaces

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