How to check if a string has spaces in Bash shell

Question

Say a string might be like "a b '' c '' d". How can I check that there is single/double quote and space contained in the string?

Answer 1

You can use regular expressions in bash:

string="a b '' c '' d"
if [[ "$string" =~ \ |\' ]]    #  slightly more readable: if [[ "$string" =~ ( |\') ]]
then
   echo "Matches"
else
   echo "No matches"
fi

Edit:

For reasons obvious above, it's better to put the regex in a variable:

pattern=" |'"
if [[ $string =~ $pattern ]]

And quotes aren't necessary inside double square brackets. They can't be used on the right or the regex is changed to a literal string.

Answer 2

case "$var" in  
     *\ * )
           echo "match"
          ;;
       *)
           echo "no match"
           ;;
esac

Answer 3

You could do this, without the need for any backslashes or external commands:

# string matching

if [[ $string = *" "* ]]; then
  echo "string contains one or more spaces"
else
  echo "string doesn't contain spaces"
fi

# regex matching

re="[[:space:]]+"
if [[ $string =~ $re ]]; then
  echo "string contains one or more spaces"
else
  echo "string doesn't contain spaces"
fi

Based on this benchmark, the string match is much faster than the regex one.

---

Related:

• How to check if a string contains a substring in Bash

Answer 4

[[ "$str" = "${str%[[:space:]]*}" ]] && echo "no spaces" || echo "has spaces"

Answer 5

string="a b '' c '' d"
if [ "$string" == "${string//[\' ]/}" ]
then 
   echo did not contain space or single quote
else
   echo did contain space or single quote
fi

Answer 6

The portable way to do this is with grep:

S="a b '' c '' d"
if echo $S | grep -E '[ "]' >/dev/null
then
  echo "It's a match"
fi

...a bit ugly, but guaranteed to work everywhere.

Answer 7

How about an approach similar to:

$ A="some string"; echo $A | grep \  | wc -l
1
$ A="somestring"; echo $A | grep \  | wc -l
0

?

Answer 8

function foo() {
    echo "String: $*"
    SPACES=$(($#-1))
    echo "Spaces: $SPACES"
    QUOTES=0
    for i in $*; do
        if [ "$i" == "'" ]; then
            QUOTES=$((QUOTES+1))
        fi
    done
    echo "Quotes: $QUOTES"
    echo
}

S="string with spaces"
foo $S
S="single' 'quotes"
foo $S
S="single '' quotes"
foo $S
S="single ' ' quotes"
foo $S

yields:

String: string with spaces
Spaces: 2
Quotes: 0

String: single' 'quotes
Spaces: 1
Quotes: 0

String: single '' quotes
Spaces: 2
Quotes: 0

String: single ' ' quotes
Spaces: 3
Quotes: 2

Answer 9

What about this:

[[ $var == ${var//[ \"]/_} ]] && echo "quotes or spaces not found"

or if you like this:

if [[ $var == ${var//[ \"]/_} ]] ; then  
   echo "quotes or spaces not found" 
else
   echo "found quotes or spaces"
fi

Explanation: I'm evaluating a comparison between the variable ${var} and the variable ${var} itself after a on-the-fly non-destructive string substitution of all the quotes and spaces with an underscore.

Examples:

${var// /_}  # Substitute all spaces with underscores

The following code substitute all characters between the squared brackets (space and quotes) with an underscore. Note that quotes has to be protected with backslash:

${var//[ \"]/_}  

Answer 10

I do wonder why nobody mentioned the [:space:] set. Usually your not only interested in detecting the space character. I often need to detect any white space, e.g. TAB. The "grep" example would look like this:

$ echo " " | egrep -q "[:space:]" && echo "Has no Whitespace" || echo "Has Whitespace"
Has Whitespace
$ echo "a" | egrep -q "[:space:]" && echo "Has no Whitespace" || echo "Has Whitespace"
Has no Whitespace