got up to python scripts

_subsections/lesson-02.org

@@ -8,6 +8,9 @@
 - [[../toc.org][TOC | Missing Semester]]
 - [[https://www.youtube.com/playlist?list=PLyzOVJj3bHQuloKGG59rS43e29ro7I57J][Playlist: Missing Semester]]
 
+- Curr: https://youtu.be/kgII-YWo3Zw?si=Hy3Vic8blG1mOc7F&t=1357
+
+
 *** timestamps
 :PROPERTIES:
 :CUSTOM_ID: timestamp
@@ -16,7 +19,7 @@
 #+attr_html: :class playlist
 + [[https://www.youtube.com/watch?v=kgII-YWo3Zw&t=54s][00:54 - control flow functions]]
 + [[https://www.youtube.com/watch?v=kgII-YWo3Zw&t=227s][03:47 - sequential execution]]
-+ [[https://www.youtube.com/watch?v=kgII-YWo3Zw&t=425s][07:05 - standard input]] *current*
++ [[https://www.youtube.com/watch?v=kgII-YWo3Zw&t=425s][07:05 - standard input]]
 + [[https://www.youtube.com/watch?v=kgII-YWo3Zw&t=444s][07:24 - error code]]
 + [[https://www.youtube.com/watch?v=kgII-YWo3Zw&t=517s][08:37 - logical operators]]
 + [[https://www.youtube.com/watch?v=kgII-YWo3Zw&t=603s][10:03 - concatenate commands]]
@@ -24,7 +27,7 @@
 + [[https://www.youtube.com/watch?v=kgII-YWo3Zw&t=675s][11:15 - process substitution]]
 + [[https://www.youtube.com/watch?v=kgII-YWo3Zw&t=935s][15:35 - comparison operator]]
 + [[https://www.youtube.com/watch?v=kgII-YWo3Zw&t=1173s][19:33 - curly braces]]
-+ [[https://www.youtube.com/watch?v=kgII-YWo3Zw&t=1359s][22:39 - python script]]
++ [[https://www.youtube.com/watch?v=kgII-YWo3Zw&t=1359s][22:39 - python script]] *current*
 + [[https://www.youtube.com/watch?v=kgII-YWo3Zw&t=1707s][28:27 - man command]]
 + [[https://www.youtube.com/watch?v=kgII-YWo3Zw&t=2175s][36:15 - finding files]]
 + [[https://www.youtube.com/watch?v=kgII-YWo3Zw&t=2190s][36:30 - grep]]
@@ -98,7 +101,8 @@ mcd() {
 
 - this will create a new directory and cd into it as per the definied functioned
 
-*** variables
+** error codes
+*** commands to access codes or values
 - $0 -- name of the script we are currently in
   - if you run this in the shell it will display 'bash'
 - $1->$9 -- the first through ninth argument given to a script
@@ -112,3 +116,140 @@ mcd() {
  ls -lah
  sudo !!
  #+end_src
+
+*** code values
+- boolean
+  - true returns an error code of 0
+  - false returns an error code of 1
+
+** using $@ and $*
+- represents all the arguments passed to a script or a function as separate, individual strings. It preserves each argument as a distinct item, even if the argument contains spaces.
+
+*** key points about $@
+1. All Arguments: It refers to all the command-line arguments passed to the script.
+2. Preserves Spaces: If an argument contains spaces, it is treated as a single argument.
+3. Usage: It is commonly used in a loop to iterate over each argument.
+
+*** example
+#+begin_src bash
+./myscript.sh file1.txt "file with spaces.txt" file3.txt
+#+end_src
+
+then $@ will be
+=file1.txt "file with spaces.txt" file3.txt=
+
+*** differences between $*
+- *$@* treats each argument as a sepearte item
+- *$** treats all arguments as a single, combined string
+
+
+** logical operators
+- you can use the error return value in conditionals
+*** example using the OR conditional
+  #+begin_src bash
+  false || echo "Oops fail"
+  "Oops fail"
+  #+end_src
+
+*** example using the AND conditional
+  #+begin_src bash
+  true && echo "this will print"
+  "this will print"
+  #+end_src
+
+** concatenate commands
+- you caoncatinate commands using the semicolon: *;*
+
+  #+begin_src bash
+  false; echo "this prints always"
+  "this prints always"
+  #+end_src
+
+** common substitution
+- take the output of a command and put it in a variable
+ #+begin_src bash
+ foo=$(pwd)
+ echo $foo
+ "/Users/ronny/..."
+ #+end_src
+
+- this can also be done by placing that format in a string and it will expand the string
+  #+begin_src bash
+  echo "the pwd output is: $(pwd)"
+  "the pwd output is: /Users/ronny/..."
+  #+end_src
+
+** process substitution
+*** description
+Bash process substitution is a feature that allows you to use the output of a command or a process as if it were a file. It enables you to redirect input or output between processes in a flexible way without needing intermediate temporary files.
+
+*** Syntax
+- creates a temporary file descriptor for the output of the command, which can be used as an input file in another command.
+  #+begin_src bash
+   <(command)
+  #+end_src
+- creates a temporary file descriptor for writing to the command, which can be used as an output file in another command.
+  #+begin_src bash
+   >(command)
+  #+end_src
+
+*** examples
+- this will take b, a, d, c and sort it so the result is 'a, b, c, d'
+  #+begin_src bash
+  sort <(echo -e "b\na") <(echo -e "d\nc")
+  #+end_src
+
+- this will list the files, send the list to *tee* which will split a portion off to the screen and the rest to grep, followed by text_files.txt
+
+  #+begin_src bash
+  ls | tee >(grep "txt" > text_files.txt)
+  #+end_src
+
+#+begin_src bash
+echo "Starting program at $(date)" # Date will be substituted
+echo "Running program $0 with $# arguments with pid $$"
+
+for file in "$@"; do
+    grep foobar "$file" > /dev/null 2> /dev/null
+
+    # when pattern is not found, grep has exit status 1
+    # we redirect STDOUT and STDERR to a null register since we do not care about them
+
+    if [[ "$?" - ne 0 ]]; then
+        echo "File $file does not have any foober adding one"
+        echo "# foobar" >> "$file"
+     fi
+done
+#+end_src
+
+- *$$* pid given for program
+- *$#* number of arguments
+- *$@* expands to all the arguments
+  - can be used in a for loop
+- *2>* refers to STDERR
+- *>* refers to STDOUT
+
+** test utility
+
+test is a bash utility that you can use to test the condition of a file.  look at the man page for more info
+
+** curly braces
+curly braces are used as a form of program command expansion.
+
+the braces contain a number of arguments seperated by commans that will expand into arguments for the program
+
+*** example
+#+begin_src bash
+touch foo{,1,2,10}
+touch foo foo1 foo2 foo10
+
+cp foo{,.old}
+cp foo foo.old
+#+end_src
+
+*** ranges
+this takes the format {1..20}
+
+#+begin_src bash
+touch directory{1..4}/foo{a..z}.txt
+#+end_src