use conditional in bash script to check string argument

Question

What about the shorter :

#!/bin/bash

[[ $1 == A ]] && echo "A" || echo "not A"

?

And a beginner version (identical logic) :

#!/bin/bash

if [[ $1 == A ]]; then
    echo "A"
else
    echo "not A"
fi

Like Scott said, you have a syntax error (missing space).

explanations

I use boolean logic here. [[ $1 == A ]] is executed, and then if its true, echo "A" is executed, and if it’s false, echo "not A" is executed, See http://mywiki.wooledge.org/BashGuide/TestsAndConditionals
[[ is a bash keyword similar to (but more powerful than) the [ command. See http://mywiki.wooledge.org/BashFAQ/031 and http://mywiki.wooledge.org/BashGuide/TestsAndConditionals Unless you’re writing for POSIX sh, I recommend [[.