How to compare strings in Bash

Question

How do I compare a variable to a string (and do something if they match)?

Answer 1

a="abc"
b="def"

# Equality Comparison
if [ "$a" == "$b" ]; then
    echo "Strings match"
else
    echo "Strings don't match"
fi

# Lexicographic (greater than, less than) comparison.
if [ "$a" \< "$b" ]; then
    echo "$a is lexicographically smaller then $b"
elif [ "$a" \> "$b" ]; then
    echo "$b is lexicographically smaller than $a"
else
    echo "Strings are equal"
fi

Notes:

1. Spaces between if and [ and ] are important
2. > and < are redirection operators so escape it with \> and \< respectively for strings.