• ls -l folder/ - means we are executing the program /bin/ls with arguments [‘l’, ‘folder/’]

• Arguments will consists of mixture of flags and regular strings. Flags can be identified because they are prceded by dash (-) or double-dash (- -).

• single dash flags can be grouped like,

  ls -l -a is equivalent

What is the shell?

Shell is a textual interface. Terminal is the virtual interface to a shell. In linux and macos, it is called bash (Bourne Again SHell).

Navigating in the shell

• The prompt we see in a terminal when we open it for the first time looks like below,

  rashid:~$

  Here rashid the machine and the current directory is ~ (short for “home”). The $ tells you that you are not the root user. ~ is called tilde.

  Eg:

  rashid:~$ date
January 8, 2026 1:15:24 AM

  rashid:~$ echo hello
hello

• The command “cd” means change directory. The command “pwd” means present working directory.

What is available in the shell?

• When the shell is asked to execute a command, it consult an environment variable called $PATH. The command “ls” lists all the files in the directory.

• cat - content of the file

• echo is the argument parsing.

• “man” (manual) is the program that explain how to use a program. or we can use -- help after writing the program name. for eg: date --help.

• tool: ZOxide tool which remember all the paths we cd into.

• Double tapping the tab key after enetering the first letter , it will show all the possible options.

• rashid@LAPTOP-G15TMEFH:~$ which -a sh /usr/bin/sh /bin/sh

• head -n1 data , for print 1st line.

• grep is a powerful command-line utility used for searching plain-text data for lines that match a specific pattern, which is typically a regular expression. Its name stands for "global regular expression print".
  grep [OPTION...] PATTERNS [FILE...]

• sed

• glob is for path, like */*.md

• find for finding the files. For eg:
  rashid@LAPTOP-G15TMEFH:~/assignments$ find -type f -mtime +15
./test2.txt
./New Rich Text Format.rtf
./test1.txt
  here, we are trying to find files which are more than 15 days old.

• rashid:~$ find ~/Downloads -type f -name "*.zip" -mtime +30
  Finds ZIP files in the download directory that are older than 30 days.

• awk program is used to parse data

• ls -l file.sh give more details about the file including its permission.

• chmod +x file.sh means, change the mode, make it executable.

The shell language (bash)

The pipes ( | ) let you string together output of one program with the input of another.

The command >file let you take the output and write it to file. The command »file let you take the output and append it to file.

#!/bin/bash is the shebang and specifies that the script should be executed using the Bash shell located at the path /bin/bash.

1. https://tom.preston-werner.com/2009/05/19/the-git-parable.html

2. https://learngitbranching.js.org/

Under the condition of unprecedented, transformative, and surprising change, the quantitative models and methods may become counterproductive or insufficient.

Predictions are not always true.

Robust Decision Making (RDM), informs good decisions without requiring confidence in and agreement on predictions. The basic idea of RDM is that, instead of reliying upon models and data, hundreds to thousand of scenarios are generated using models to describe how plans prforms in these plausible futures. Then, future conditions in which the plans perform well is distinguished using visualizationa and statistical analysis.

The traditional predict-then-act framework may leads to gridlock or overconfidence, when the predictions are in accurate or controversial.

Analytics - the discovery and communication of meaningful patterns in quantitative information.

Deep uncertainty - when the parties to a decision do not know or agree on the best model for relating actions to consequences or the model to represent the future or the likelihood of the future events.

RDM put forward the backward analysis, that is beginning with a proposed decision or plan and testing the plan against many different plausible futures.

RDM combines two approaches, scenrios and probablistic analysis. The steps involved in the RDM analysis are, decision structuring, case generation, scenario discovery, and then trad-off analysis.

Robsutness and flexibility can provide the best response to deeply uncertain future conditions.