How to check if a string contains a substring in Bash

Question

I have a string in Bash:

string=\"My string\"

How can I test if it contains another string?

if [ $string ?? \'foo\' ]; then         


        

Answer 1

So there are lots of useful solutions to the question - but which is fastest / uses the fewest resources?

Repeated tests using this frame:

/usr/bin/time bash -c 'a=two;b=onetwothree; x=100000; while [ $x -gt 0 ]; do TEST ; x=$(($x-1)); done'

Replacing TEST each time:

[[ $b =~ $a ]]           2.92 user 0.06 system 0:02.99 elapsed 99% CPU

[ "${b/$a//}" = "$b" ]   3.16 user 0.07 system 0:03.25 elapsed 99% CPU

[[ $b == *$a* ]]         1.85 user 0.04 system 0:01.90 elapsed 99% CPU

case $b in *$a):;;esac   1.80 user 0.02 system 0:01.83 elapsed 99% CPU

doContain $a $b          4.27 user 0.11 system 0:04.41 elapsed 99%CPU

(doContain was in F. Houri's answer)

And for giggles:

echo $b|grep -q $a       12.68 user 30.86 system 3:42.40 elapsed 19% CPU !ouch!

So the simple substitution option predictably wins whether in an extended test or a case. The case is portable.

Piping out to 100000 greps is predictably painful! The old rule about using external utilities without need holds true.

Answer 2

I like sed.

substr="foo"
nonsub="$(echo "$string" | sed "s/$substr//")"
hassub=0 ; [ "$string" != "$nonsub" ] && hassub=1

Edit, Logic:

• Use sed to remove instance of substring from string

• If new string differs from old string, substring exists

Answer 3

I am not sure about using an if statement, but you can get a similar effect with a case statement:

case "$string" in 
  *foo*)
    # Do stuff
    ;;
esac

Answer 4

The accepted answer is best, but since there's more than one way to do it, here's another solution:

if [ "$string" != "${string/foo/}" ]; then
    echo "It's there!"
fi

${var/search/replace} is $var with the first instance of search replaced by replace, if it is found (it doesn't change $var). If you try to replace foo by nothing, and the string has changed, then obviously foo was found.

Answer 5

Bash 4+ examples. Note: not using quotes will cause issues when words contain spaces, etc. Always quote in Bash, IMO.

Here are some examples Bash 4+:

Example 1, check for 'yes' in string (case insensitive):

    if [[ "${str,,}" == *"yes"* ]] ;then

Example 2, check for 'yes' in string (case insensitive):

    if [[ "$(echo "$str" | tr '[:upper:]' '[:lower:]')" == *"yes"* ]] ;then

Example 3, check for 'yes' in string (case sensitive):

     if [[ "${str}" == *"yes"* ]] ;then

Example 4, check for 'yes' in string (case sensitive):

     if [[ "${str}" =~ "yes" ]] ;then

Example 5, exact match (case sensitive):

     if [[ "${str}" == "yes" ]] ;then

Example 6, exact match (case insensitive):

     if [[ "${str,,}" == "yes" ]] ;then

Example 7, exact match:

     if [ "$a" = "$b" ] ;then

Example 8, wildcard match .ext (case insensitive):

     if echo "$a" | egrep -iq "\.(mp[3-4]|txt|css|jpg|png)" ; then

Enjoy.

Answer 6

msg="message"

function check {
    echo $msg | egrep [abc] 1> /dev/null

    if [ $? -ne 1 ];
    then 
        echo "found" 
    else 
        echo "not found" 
    fi
}

check

This will find any occurance of a or b or c