Is there a unix scripting file checking Key?

Question

Is there a key that explains theese letters such as -n, -d, etc all mean ?

Example:

if [[ -d ${directory_name} ]]; then ...; fi

What is the -d or where do I find a key?

Example:

while [[ -n ${variable_name} ]]; do ...; done

what is the -n mean??

Is there a guide that explains what all of these -n, -e, -a, -d, -s, -h, etc?

I do a lot of Unix shell scripting modifications, and I've seen these arguments used inside the loops or if then statements on variables and file locations etc.

I'm looking for a place that explains each of the arguments as mentioned above for scripting.

Answer 1

you want the TLDP page for BASH,

advanced bash: http://www.tldp.org/LDP/abs/html/index.html

beginner bash: http://tldp.org/LDP/Bash-Beginners-Guide/html/index.html

what you were asking is about file test operators and can be found here: http://www.tldp.org/LDP/abs/html/fto.html

and also bash conditional expressions which can found here: http://www.gnu.org/software/bash/manual/html_node/Bash-Conditional-Expressions.html

-d  file is a directory
-f  file is a regular file
-e  file exists
-s  file size is not zero
-b  file is a block device
-h  file is a symbolic link
-w  file has write permissions for user executing this bash statement
{there are more}

#!/bin/bash
if [ -e $1 ] && [ -w $1 ]; then
   echo "the file you entered was "$1" and it exists and you have write permission to it"
else
   echo "condition failed for exist and for write permission"
fi

Answer 2

I believe you should find everything in details in the man page of your shell (e.g. man bash).

Moreover, bash, for one, has a builtin command named help. Just give the command in parameter. Here the command is [[ and help [[ redirects to the command test (a.k.a. [), therefore help test will give you what you need.

Finally, builtins often have their standalone counterparts in /bin and their are generally provided with a manpage => man [ or man test