bash check if a variable starts with 'fatal'

Question

I have a variable in bash:

branchName=$(git branch --show-current)

There are two options for the returned value:

• banch name (e.g. master)
• fatal: not a git repository (or any of the parent directories): .git

I want to check if branchName starts with fatal:

I have tried to check if it starts with master and it works:

if [[ $branchName == master* ]];
    then echo "yes"
fi
echo $branchName

Output:
yes
master

but when I try to check if it starts with fatal: it does not work:

if [[ $branchName == fatal* ]];
    then echo "yes"
fi

Output:
fatal: not a git repository (or any of the parent directories): .git

Answer 1

but when I try to check if it starts with fatal: it does not work:

It's because this is an error message and goes to stderr. What you capture is only the stdout.

A better approach is to check the return value instead. E.g.

if branchName=$(git branch --show-current 2>/dev/null); then
    echo "Branch is: $branchName"
else
    echo "Error: can't get branch name"
fi

(If command succeeds, it'd return 0; any non-zero value is usually treated as failure. The if statement above would be "true" when git return 0).

But if you do want to capture stderr, you can do:

branchName=$(git branch --show-current 2>&1)