Bash script creates a file which it shouldn't be

This following script will creates a file named "Happy", i couldn't figure out why, can someone try this script and tell me what is happening? Thanks!

#!/bin/bash

str1=""
str2="Sad"
str3="Happy"

if [ "$str2">"$str3" ]
    then echo "$str2 is greater than $str3"
elif [ "$str2"<"$str3" ]
    then echo "$str2 is less than $str3"
fi

Solution

[ is just a (silly) alias for the test command; everything following it (including the mandatory closing ]) is an argument. (What you have is treated the same as if test "$str2">"$str3".)

There are two issues:

The operands and the operators need to be separated by whitespace.
```
# still not quite right, but ...
if [ "$str2" > "$str3" ]
```
Since > and < are interpreted as redirection operators by the shell, they have to be escaped so that they are passed as arguments to [.
```
if [ "$str2 \> "$str3" ]
```

(You might think just escaping the operator would be sufficient; however, "$str2"\>"$str3" would be treated as a single string argument to test rather than three separate arguments which test will interpret as an expression. test "$str2"\>"$str3" would simply check if the single argument is empty or not.)

Since you are using bash, it's far simpler to just use [[ instead of [. [[ is not a regular command; it's special syntax recognized by bash, so that normal processing rules don't apply. Most relevant here is that > is a string comparison operator, not a redirection operator, so it doesn't need to be escaped.

    if [[ $str2 > $str3 ]]