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You can always check the man page of your shell. man bash says: Special Parameters # Expands to the number of positional parameters in decimal. Therefore a shell script can check how many parameters are given with code like this: if [ "$#" -eq 0 ]; then echo "you did not pass any parameter" fi
$0-The filename of the current script. $#-The number of arguments supplied to a script. $$-The process number of the current shell. For shell scripts, this is the process ID under which they are executing.
Nov 16, 2018 · If any file argument to one of the primaries is of the form /dev/fd/n, then file descriptor n is checked. If the file argument to one of the primaries is one of /dev/stdin, /dev/stdout, or /dev/stderr, file descriptor 0, 1, or 2, respectively, is checked.
Jul 25, 2017 · $# is the number of positional parameters passed to the script, shell, or shell function. This is because, while a shell function is running, the positional parameters are temporarily replaced with the arguments to the function. This lets functions accept and use their own positional parameters.
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). If it doesn't exist, you should get a number other then 0.
Mar 15, 2023 · In this article, we’ll provide an in-depth guide to all bash special variables, including examples of their usage and common pitfalls to avoid. ` $0 ` – The name of the script being executed. ` $1-$9 ` – The first nine command-line arguments. ` $# ` – The number of command-line arguments.
Aug 1, 2019 · In Linux: when a process calls the exit system call, the kernel stores the value passed to the system call (an int) even after the process dies. The exit system call is called by the exit() ANSI C function, and indirectly when you do return from main.
Aug 5, 2023 · Write a shell script that runs a command or series of commands for a fixed set of files. Run a shell script from the command line. Write a shell script that operates on a set of files defined by the user on the command line. Create pipelines that include shell scripts you, and others, have written.
Mar 31, 2022 · When you first launch the shell, it uses a startup script located in the .bashrc or .bash_profile file which allows you to customize the behavior of the shell. When a shell is used interactively, it displays a $ when it is waiting for a command from the user. This is called the shell prompt.
This is a quick reference guide to the meaning of some of the less easily guessed commands and codes of shell scripts. By their nature, they are also quite difficult to find using search engines. These examples include process management, shell scripts arguments, and shell script test conditions.
