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<code> , Operator Description , ! EXPRESSION The EXPRESSION is false. , -n STRING The length of STRING is greater than zero. , -z STRING The lengh of STRING is zero (ie it is empty). , STRING1 = STRING2 STRING1 is equal to STRING2 , STRING1 != STRING2 STRING1 is not equal to STRING2 , INTEGER1 -eq INTEGER2 INTEGER1 is numerically equal to INTEGER2 , INTEGER1 -gt INTEGER2 INTEGER1 is numerically greater than INTEGER2 , INTEGER1 -lt INTEGER2 INTEGER1 is numerically less than INTEGER2 , -d FILE FILE exists and is a directory. , -e FILE FILE exists. , -r FILE FILE exists and the read permission is granted. , -s FILE FILE exists and its size is greater than zero (ie. it is not empty). , -w FILE FILE exists and the write permission is granted. , -x FILE FILE exists and the execute permission is granted. , , $0 - The name of the Bash script. , $1 - $9 - The first 9 arguments to the Bash script. (As mentioned above.) , $# - How many arguments were passed to the Bash script. , $@ - All the arguments supplied to the Bash script. , $? - The exit status of the most recently run process. , $$ - The process ID of the current script. , $USER - The username of the user running the script. , $HOSTNAME - The hostname of the machine the script is running on. , $SECONDS - The number of seconds since the script was started. , $RANDOM - Returns a different random number each time is it referred to. , $LINENO - Returns the current line number in the Bash script. , , </code>