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2. What is the $? (dollar question mark) variable in shell...

   stackoverflow.com/questions/6834487

   344. $? is used to find the return value of the last executed command. Try the following in the shell: ls somefile. echo $? If somefile exists (regardless whether it is a file or directory), you will get the return value thrown by the ls command, which should be 0 (default "success" return value).

3. What is the purpose of "&&" in a shell command? - Stack Overflow

   stackoverflow.com/questions/4510640

   In shell, when you see. $ command one && command two. the intent is to execute the command that follows the && only if the first command is successful. This is idiomatic of Posix shells, and not only found in Bash. It intends to prevent the running of the second process if the first fails.

4. shell - How can I compare numbers in Bash? - Stack Overflow

   stackoverflow.com/questions/18668556

   To make it shorter for use, use this function: compare_nums() {. # Function to compare two numbers (float or integers) by using AWK. # The function will not print anything, but it will return 0 (if the comparison is true) or 1. # (if the comparison is false) exit codes, so it can be used directly in shell one liners.

5. scripting - What is the difference between $@ and $* in shell...

   stackoverflow.com/questions/2761723

   A key difference from my POV is that "$@" preserves the original number of arguments. It's the only form that does. For that reason it is very handy for passing args around with the script. For example, if file my_script contains: echo 'MAIN sees ' $# ' args'. and I run it like this:

6. Automate scp file transfer using a shell script - Stack Overflow

   stackoverflow.com/questions/1346509

   Automating SSH and running SCP and other commands in shell scripting. 4. Bash Script for Secure transfer. 1.

7. shell - How do I split a string on a delimiter in Bash ... -...

   stackoverflow.com/questions/918886

   For instance: on my Debian GNU/Linux, there is a standard shell called dash; I know many people who like to use another shell called ksh; and there is also a special tool called busybox with his own shell interpreter . For posix shell compatible answer, go to last part of this answer! Requested string. The string to be split in the above ...

8. string - Extract substring in Bash - Stack Overflow

   stackoverflow.com/questions/428109

   In case someone wants more rigorous information, you can also search it in man bash like this. $ man bash [press return key] /substring [press return key] [press "n" key] [press "n" key] [press "n" key] [press "n" key] Result: ${parameter:offset}

9. How to use double or single brackets, parentheses, curly braces

   stackoverflow.com/questions/2188199

   In Bash, test and [ are shell builtins. The double bracket [[, which is a shell keyword, enables additional functionality. For example, you can use && and || instead of -a and -o and there's a regular expression matching operator =~. Also, in a simple test, double square brackets seem to evaluate quite a lot quicker than single ones.

10. regex - Meaning of "=~" operator in shell script - Stack Overflow

    stackoverflow.com/questions/12454731

    An additional binary operator, =~, is available, with the same precedence as == and !=. When it is used, the string to the right of the operator is considered an extended regular expression and matched accordingly (as in regex (3)). The return value is 0 if the string matches the pattern, and 1 otherwise.

11. Shell scripting: -z and -n options with if - Unix & Linux Stack...

    unix.stackexchange.com/questions/109625

    To extend terdon's answer, I found that Unix / Linux - Shell Basic Operators on Tutorials Point also includes file-related operators (as well as other useful ones). -b file Checks if file is a block special file; if yes, then the condition becomes true.