IT Systems, Networks, Security and Education
I recently worked on a migration from OpenVMS to Red Hat Linux, and spent some serious effort porting VMS DCL (Direct Command Line) scripts to Python and Bash. The long-time VMS people were completely unfamiliar with the Linux command line, so we went looking for some good online resources that mapped DCL to Bash. (See …
Continue reading “OpenVMS Commands Mapped to Unix/Linux Equivalents”
This is post 11 of 11 in the series “The Linux Command Line” The first principle of file creation is that when you, as a specific user, create a file, it will be owned by you, and your default group will have some default permissions set on that file. Remember the User – Group – …
Continue reading “Linux: Creating and Deleting Directories and Files”
This is post 10 of 11 in the series “The Linux Command Line” The ls Command ls = List of objects in the current working directory. Typing: ls will bring up a list of files and subdirectories. It may also be flagged to provide some different ways of looking at the list of files, such …
Continue reading “Listing Files and Going Deep Into Filesystems”
This is post 5 of 11 in the series “The Linux Command Line” When you start a shell session, it opens in your home directory. This is true in all OSs, and even the paths are similar. In Windows: C:\Users\username\ In Mac: /Users/username/ In Linux: /home/username/ or /users/username/ Why home? It keeps your stuff segregated …
This is post 3 of 11 in the series “The Linux Command Line” Boot, login, and start Secure Telnet/Secure Shell or PuTTY. Log in with your UNM user name and password. Check Your Shell Command: echo $SHELL Your answer may be: /bin/sh # the Bourne shell /bin/csh # the C shell /bin/bash # the Bourne …
This is post 2 of 11 in the series “The Linux Command Line” Let’s be clear: the structure of directories in any OS is a directory tree. You, I and everyone will want to call it a “file system.” That’s okay, and the other kids usually won’t laugh at you. But formally, a file system …
This is post 13 of 19 in the series “[ Shell Scripting ]” Arguments For our first trick, we’re going to write a script that shows us how arguments are dealt with by scripts. Start a new script called args. (Notice that it doesn’t have to be “args.sh”.) Create the script: #!/bin/bash if [ $# …
This is post 12 of 19 in the series “[ Shell Scripting ]” The Bourne/bash shell supports a variety of conditionals, loops and other flow control operations. You’ll use these often. if The if statement is a simple conditional. Its syntax is: if condition ; then commands [elif condition ; then commands]… [else commands] fi …
This is post 11 of 19 in the series “[ Shell Scripting ]” Redirection Operators These operators redirect: standard input (0), standard output (1) and standard error (2). > redirects standard output to a file ps aux > file_name Creates a file and writes standard output. Clobbers any existing file. >> appends standard output to …
This is post 10 of 19 in the series “[ Shell Scripting ]” Any number of commands can be pipelined together. command1 | command2 The above command creates a pipe: the standard output of command1 is connected to the standard input of command2. Any command that can accept Standard Input and produce Standard Output is …