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

My .bash_profile file and how I used grep:

If the PATH environment variable includes my two bin directories, don't append them,

# .bash_profile
# Get the aliases and functions
if [ -f ~/.bashrc ]; then
    . ~/.bashrc
fi

U=~/.local.bin:~/bin

if ! echo "$PATH" | grep -q "home"; then
    export PATH=$PATH:${U}
fi

Answer 2

I found to need this functionality quite frequently, so I'm using a home-made shell function in my .bashrc like this which allows me to reuse it as often as I need to, with an easy to remember name:

function stringinstring()
{
    case "$2" in
       *"$1"*)
          return 0
       ;;
    esac
    return 1
}

To test if $string1 (say, abc) is contained in $string2 (say, 123abcABC) I just need to run stringinstring "$string1" "$string2" and check for the return value, for example

stringinstring "$str1" "$str2"  &&  echo YES  ||  echo NO

Answer 3

You should remember that shell scripting is less of a language and more of a collection of commands. Instinctively you think that this "language" requires you to follow an if with a [ or a [[. Both of those are just commands that return an exit status indicating success or failure (just like every other command). For that reason I'd use grep, and not the [ command.

Just do:

if grep -q foo <<<"$string"; then
    echo "It's there"
fi

Now that you are thinking of if as testing the exit status of the command that follows it (complete with semi-colon), why not reconsider the source of the string you are testing?

## Instead of this
filetype="$(file -b "$1")"
if grep -q "tar archive" <<<"$filetype"; then
#...

## Simply do this
if file -b "$1" | grep -q "tar archive"; then
#...

The -q option makes grep not output anything, as we only want the return code. <<< makes the shell expand the next word and use it as the input to the command, a one-line version of the << here document (I'm not sure whether this is standard or a Bashism).

Answer 4

This Stack Overflow answer was the only one to trap space and dash characters:

# For null cmd arguments checking   
to_check=' -t'
space_n_dash_chars=' -'
[[ $to_check == *"$space_n_dash_chars"* ]] && echo found

Answer 5

grep -q is useful for this purpose.

The same using awk:

string="unix-bash 2389"
character="@"
printf '%s' "$string" | awk -vc="$character" '{ if (gsub(c, "")) { print "Found" } else { print "Not Found" } }'

Output:

Not Found

string="unix-bash 2389"
character="-"
printf '%s' "$string" | awk -vc="$character" '{ if (gsub(c, "")) { print "Found" } else { print "Not Found" } }'

Output:

Found

Original source: http://unstableme.blogspot.com/2008/06/bash-search-letter-in-string-awk.html

Answer 6

case $string in (*foo*)
  # Do stuff
esac

This is the same answer as https://stackoverflow.com/a/229585/11267590. But simple style and also POSIX Compliant.