[shell] How do you tell if a string contains another string in POSIX sh?

I want to write a Unix shell script that will do various logic if there is a string inside of another string. For example, if I am in a certain folder, branch off. Could someone please tell me how to accomplish this? If possible I would like to make this not shell specific (i.e. not bash only) but if there's no other way I can make do with that.

#!/usr/bin/env sh

if [ "$PWD" contains "String1" ]
then
    echo "String1 present"
elif [ "$PWD" contains "String2" ]
then
    echo "String2 present"
else
    echo "Else"
fi

Pure POSIX shell:

#!/bin/sh
CURRENT_DIR=`pwd`

case "$CURRENT_DIR" in
  *String1*) echo "String1 present" ;;
  *String2*) echo "String2 present" ;;
  *)         echo "else" ;;
esac

Extended shells like ksh or bash have fancy matching mechanisms, but the old-style case is surprisingly powerful.

If you want a ksh only method that is as fast as "test", you can do something like:

contains() # haystack needle
{
    haystack=${1/$2/}
    if [ ${#haystack} -ne ${#1} ] ; then
        return 1
    fi
    return 0
}

It works by deleting the needle in the haystack and then comparing the string length of old and new haystacks.

#!/usr/bin/env sh

# Searches a subset string in a string:
# 1st arg:reference string
# 2nd arg:subset string to be matched

if echo "$1" | grep -q "$2"
then
    echo "$2 is in $1"
else 
    echo "$2 is not in $1"
fi

case $(pwd) in
  *path) echo "ends with path";;
  path*) echo "starts with path";;
  *path*) echo "contains path";;
  *) echo "this is the default";;
esac

test $(echo "stringcontain" "ingcon" |awk '{ print index($1, $2) }') -gt 0 && echo "String 1 contain string 2"

--> output: String 1 contain string 2

There's Bash regular expressions. Or there's 'expr':

 if expr "$link" : '/.*' > /dev/null; then
    PRG="$link"
  else
    PRG=`dirname "$PRG"`/"$link"
  fi

Here is a link to various solutions of your issue.

This is my favorite as it makes the most human readable sense:

The Star Wildcard Method

if [[ "$string" == *"$substring"* ]]; then
    return 1
fi
return 0

In special cases where you want to find whether a word is contained in a long text, you can iterate through the long text with a loop.

found=F
query_word=this
long_string="many many words in this text"
for w in $long_string; do
    if [ "$w" = "$query_word" ]; then
          found=T
          break
    fi
done

This is pure Bourne shell.

Sadly, I am not aware of a way to do this in sh. However, using bash (starting in version 3.0.0, which is probably what you have), you can use the =~ operator like this:

#!/bin/bash
CURRENT_DIR=`pwd`

if [[ "$CURRENT_DIR" =~ "String1" ]]
then
 echo "String1 present"
elif [[ "$CURRENT_DIR" =~ "String2" ]]
then
 echo "String2 present"
else
 echo "Else"
fi

As an added bonus (and/or a warning, if your strings have any funny characters in them), =~ accepts regexes as the right operand if you leave out the quotes.

See the manpage for the 'test' program. If you're just testing for the existence of a directory you would normally do something like so:

if test -d "String1"; then
  echo "String1 present"
end

If you're actually trying to match a string you can use bash expansion rules & wildcards as well:

if test -d "String*"; then
  echo "A directory starting with 'String' is present"
end

If you need to do something more complex you'll need to use another program like expr.