How to compare strings in Bash

Question

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

Answer 1

you can also use use case/esac

case "$string" in
 "$pattern" ) echo "found";;
esac

Answer 2

Or, if you don't need else clause:

[ "$x" == "valid" ] && echo "x has the value 'valid'"

Answer 3

The following script reads from a file named "testonthis" line by line and then compares each line with a simple string, a string with special characters and a regular expression. If it doesn't match, then the script will print the line, otherwise not.

Space in Bash is so much important. So the following will work:

[ "$LINE" != "table_name" ] 

But the following won't:

["$LINE" != "table_name"] 

So please use as is:

cat testonthis | while read LINE
do
if [ "$LINE" != "table_name" ] && [ "$LINE" != "--------------------------------" ] && [[ "$LINE" =~ [^[:space:]] ]] && [[ "$LINE" != SQL* ]]; then
echo $LINE
fi
done

Answer 4

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.