mjhjmtu

JavaScript has a function for this:

'world'.startsWith('w')
true

How can I test this with shell? I have this code:

if [ world = w ]
then
 echo true
else
 echo false
fi

but it fails because it is testing for equality. I would prefer using a builtin,
but any utilities from this page would be acceptable:

http://pubs.opengroup.org/onlinepubs/9699919799/idx/utilities.html

If your shell is bash: within double brackets, the right-hand side of the == operator is a pattern unless fully quoted:

if [[ world == w* ]]; then
 echo true
else
 echo false
fi

Or more tersely: [[ world == w* ]] && echo true || echo false [*]

If you are not targetting bash specifically: use the case statement for pattern matching

case "world" in
 w*) echo true ;;
 *) echo false ;;
esac

[*] but you need to be careful with the A && B || C form because C will be executed if either A fails or B fails. The if A; then B; else C; fi form will only execute C if A fails.

set world

Then:

if [ "$1%%w*" ]
then
 echo false
else
 echo true
fi

1. Aggressively remove substring starting with w from source string


2. If anything left, then source string does not start with second string

Or:

if [ "$1" = "$1#w" ]
then
 echo false
else
 echo true
fi

1. Remove w from source string


2. Compare with source string


3. If equal, then source string does not start with second string