What Does the -T Flag Mean in a Shell Script If Statement?
I'm Not Sure What the -T Flag Means for Unix Shell Scripts Since I Can't Find Any Mention of It Online. I Ran into an If Statement for a Bash Shell Shell...
I'm not sure what the -t flag means for unix shell scripts since I can't find any mention of it online.
I ran into an if statement for a bash shell shell script. I've included a sanitized snippet:
source "${BASH_SOURCE%/*}"/some_script
if [[ ! -t 0 ]] && [[ $(id -u) == 0 ]]; then
echo 'got here'
else
echo 'no get here'
fi
I don't understand what the "-t" flag in the test command. I assume it doesn't have anything to do with testing files since it didn't appear with the other file testing flags I found and because 0 is not a file.
Thanks in advance.
1 Answer
-t means:
True if file descriptor is open and refers to a terminal.
In this case, file descriptor 0 is standard input, so it's checking to see if standard input is coming from the terminals.
For a complete list of these file descriptors, run man bash and search for "CONDITIONAL EXPRESSIONS".
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