Autosave: 2023-03-16 06:58:39

Programming_Languages/Python/Syntax/Functions_in_Python.md

@@ -4,7 +4,7 @@ categories:
 tags: [python]
 ---
 
-# Functions
+# Functions in Python
 
 - Convention is to leave a double line-break after a function definition (but not with nested functions - here, a single linebreak is sufficient)
 - Scope within functions is demarcated by indents, as everything in Python

Programming_Languages/Python/Syntax/Lists_in_Python.md

@@ -91,7 +91,7 @@ print(a_list)
 We distinguish `del` from `remove` when removing elements from lists:
 
 - `del` requires an index value
-- `remove` requires a value reference (i.e. the mame of the element rather than its index)
+- `remove` requires a value reference (i.e. the name of the element rather than its index)
 
 `del` is simple deletion whereas `remove` searches the list. Therefore `del` is more efficient.
 

Programming_Languages/Python/Syntax/Map_and_filter_in_Python.md

@@ -26,6 +26,22 @@ x = list(map(addOne, data))
 # necessary to add `list` to get some output
 ```
 
+### Map returns an object
+
+When you run `map` against a list it returns a map object not a list. This can present problems if you are not aware of it since it is not an entity that you can loop through.
+
+The following map removes whitespaces from elements in a list:
+
+```py
+  lines = map(lambda x: x.strip(), lines)
+```
+
+In order to be able to run list-like operations against the resulting `lines` object we would need to convert it to a list:
+
+```py
+  lines = list(map(lambda x: x.strip(), lines))
+```
+
 ## Filter
 
 ```py

Programming_Languages/Shell/Case_statements_in_Bash.md

@@ -7,23 +7,30 @@ tags:
 
 # Case statements in Bash
 
+Usage against a variable
+
+```sh
+animal="dog"
+case $animal in
+    bird ) echo "Avian";;
+    dog|puppy ) echo "Canine";;
+    * ) echo "No match";;
+esac
+```
+
+Usage as part of a function:
+
 ```bash
 function convertCharToInt {
     case $1 in
         A|X )
-            echo 1
-        ;;
-
+            echo 1 ;;
         B|Y )
-            echo 2
-        ;;
-
+            echo 2 ;;
         C|Z )
-            echo 3
-        ;;
+            echo 3 ;;
         *)
-            echo 0
-        ;;
+            echo ;;
     esac
 }
 ```

Programming_Languages/Shell/Formatting_output_text_in_Bash.md

@@ -0,0 +1,57 @@
+---
+categories:
+  - Programming Languages
+tags:
+  - shell
+---
+
+# Formatting output text in Bash
+
+We can use the `-e` flag with `echo` to have greater control over the output of text. `-e` allows us to use linebreaks, tabs and other formattings within a string.
+
+## Output text in columns
+
+```bash
+echo -e  "Name\t\tNumber"; echo -e "Thomas\t\t123";
+
+Name		Number
+Thomas		123
+```
+
+## Break text over several lines
+
+```bash
+echo -e "This text\nbreaks over\nthree lines"
+
+This text
+breaks over
+three lines
+```
+
+## Colour outputs
+
+![](/_img/terminal_colours.png)
+
+```bash
+echo -e "\033[31;40mColoured Text\033[0m"
+```
+
+The coloured section is prepended by `\033[` and ended with `[0m`. The foreground colour is given first, and then the background colour.
+
+We can also change the text style. We do this by adding an extra value after the first square bracket:
+
+```bash
+echo -e "\033[4;31;40mColoured Text\033[0m"
+```
+
+This underlines the output.
+
+We can create a script that simplifies the construction of colour-formatted text, e.g
+
+```bash
+ulinered="\033[4;31;40m"
+red="\033[31;40m"
+none="\033[0m"
+
+echo -e $ulinered"ERROR:"$none$red" Something went wrong."$none
+```

Programming_Languages/Shell/Functions_in_Bash.md

@@ -7,7 +7,7 @@ tags:
 
 # Functions in Bash
 
-- We don't name function parameters in the function declaration. Instead we have an implied index of arguments: `$1, $2, $3,...`. When the function is called, the first value after the function name becomes `$1` by default.
+We don't name function parameters in the function declaration. Instead we have an implied index of arguments: `$1, $2, $3,...`. When the function is called, the first value after the function name becomes `$1` by default, then the subsequent arguments.
 
 ```bash
 function expandRange() {
@@ -24,3 +24,38 @@ expandedRange=$(expandRange 1 4)
 echo $expandedRange
 # 1 2 3 4
 ```
+
+## Get all arguments as an array
+
+We can access all the arguments passed to a function using the `$@` syntax we encountered before when [passing arguments to scripts](/Programming_Languages/Shell/Passing_arguments_to_scripts.md). (Here a function is a kind of script in miniature so the process is the same.)
+
+```sh
+function numberThings() {
+  i=1
+  for f in "$@"; do
+    echo $i: "$f"
+    (( i++ ))
+  done
+}
+```
+
+## Local variables
+
+```sh
+var1="I'm variable 1"
+
+function myfunction() {
+  var2="I'm variable 2"
+  local var3="I'm variable 3"
+}
+
+myfunction
+echo $var1
+echo $var2
+echo $var3
+
+# I'm variable 1
+# I'm variable 2
+```
+
+> The convention is to put functions at the top of the script, after the shebang and after the global variables

Programming_Languages/Shell/Grep.md

@@ -5,6 +5,8 @@ tags:
   - shell
 ---
 
+# Grep
+
 ## Purpose of `grep`
 
 `grep` stands for “global regular expression print”. It allows you to search plain text data sets for strings which match a regular expression or pattern.

Programming_Languages/Shell/Loops_in_bash.md

@@ -5,18 +5,9 @@ tags:
   - shell
 ---
 
-# Loops in bash
+# Loops in Bash
 
-## Loop through an array
-
-```bash
-for element in "${arr[@]}"
-do
-    echo "$element"
-done
-```
-
-## Traditional for loop with upper and lower increment range
+## Traditional for loop
 
 ```bash
 for (( i=0; i<=5;i++  )); do
@@ -25,3 +16,55 @@ done
 
 # 1 2 3 4 5
 ```
+
+## `for..in`: loop through an array
+
+```bash
+for element in "${arr[@]}"
+do
+    echo "$element"
+done
+```
+
+## While loop
+
+> `while` loops execute while a condition is true (0)
+
+We can use a `while` loop as a condition in two senses:
+
+- execute while a given condition obtains
+- expand and execute a given command as long as the final command in the `while' for the command has an exit status of zero (i.e. truthy)
+
+Here is an exampe of using `while` in the former case:
+
+```sh
+declare -i n=0
+while (( n<10 ))
+do
+  echo "n:$n"
+  (( n++ ))
+done
+```
+
+Here is an example of using `while` in the latter case:
+
+```sh
+while read line;
+do
+    # something
+done < "$file_to_read"
+```
+
+## Until loop
+
+> `until` loops execute until a condition is false (1)
+
+```sh
+declare -i m=0
+until (( m==10 )): do
+  echo "m:$m"
+  (( m++ ))
+done
+```
+
+This gives us the same output as `n` with the while loop but here it runs so long as `m==10` is false. As soon as `m` is equal to 100, the condition becomes true and hence the loop stops.

Programming_Languages/Shell/Passing_arguments_to_scripts.md

@@ -9,13 +9,15 @@ tags:
 
 ## Relation between commands and programs
 
-Whenever we issue a command in bash we are really running an executable program that is associated with the command. This is why when we create our own bash scripts we must run `chmod` to make them executables. When we issue a command like `./file.sh` we are running an executable program.
+Whenever we issue a command in bash we are really running an executable program that is associated with the command. This is why when we create our own bash scripts we must run `chmod` to make them executable. When we issue a command like `./file.sh` we are running an executable program.
 
-How come, however, that when we use a program like `cd` or `npm` we don’t have to type `./cd.sh` or `./npm.sh` ? Remember from our discussion of the `PATH` environment variable that whenever we use inbuilt commands like `ls` and `cd` we are automatically sourcing them from the binary directory because we have these directories in our `PATH` . Hence the shell knows in advance what these commands mean. In the case of custom scripts, these aren’t typically added to the `PATH` so we have to source them in order to run them.
+When we run a program like `cd` or `npm` we don’t have to type `./cd.sh` or `./npm.sh`. This is because a reference to the program file is already in our `$PATH`.
+
+In the case of `cd`, this is an in-built program and as such it will be sourced from a binary and we have a reference to the binary in path. In the case of `npm`, this is not an in-built program however in order to run it we must already have it in our `PATH`.
 
 ## Passing arguments
 
-If you think about it, a script is really just a function that runs when you source it. As such there needs to be a way for you to pass data to the function so that it can actually act like a function and take arguments. When we use for example `cd ./Desktop` we are passing a directory name as an argument to the `cd` program. We can do the same thing with our custom bash scripts.
+A script is really just a function that runs when you source it. As such there needs to be a way for you to pass data to the function so that it can actually act like a function and take arguments. When we use for example `cd ./Desktop` we are passing a directory name as an argument to the `cd` program. We can do the same thing with our custom bash scripts.
 
 To pass an argument we simply add the values after the script in the command. For example:
 
@@ -23,7 +25,7 @@ To pass an argument we simply add the values after the script in the command. Fo
 ./arguments.sh Thomas 33
 ```
 
-The script is as follows:
+We can use built-in variables to return information about the invocation of this script:
 
 ```bash
 #!/bin/bash
@@ -45,9 +47,8 @@ The second argument is 33
 Your name is Thomas and you are 33 years old
 ```
 
-Some points to note on syntax. The `$` is used to individuate the script itself and its arguments.
+Key points:
 
-- Each argument passed is accessible from an index starting at `1` (`$1`)
-- The script itself occupies the `0` position, hence we are able to log the name of the script at line 1 `$0` )
-- To log the arguments as a group (for instance to later loop through them) we use `$@` .
-- To get the number of arguments use `$#`
+- `$0` designates the script or function that is being executed
+- `$@` designates a list of all the arguments that are passed to the script
+- `$1...` designates each individual argument

Programming_Languages/Shell/Proper_shebang_syntax.md

@@ -0,0 +1,20 @@
+---
+categories:
+  - Programming Languages
+tags:
+  - shell
+---
+
+# Proper shebang syntax
+
+This is a more portable way of writing the shebang because the location of Bash on different systems can vary.
+
+```bash
+#!/usr/bin/env Bash
+```
+
+Rather than:
+
+```bash
+#!/bin/bash
+```

Programming_Languages/Shell/Test_values_in_Bash.md

@@ -3,6 +3,7 @@ categories:
   - Programming Languages
 tags:
   - shell
+  - regex
 ---
 
 # Test values in Bash
@@ -22,7 +23,7 @@ echo $?
 
 [ -d /bin/zsh ] # is this binary a directory?
 echo $
-01  # no
+1  # no
 ```
 
 ## Test structures
@@ -61,6 +62,14 @@ We can negate a test condition with `!`:
 0
 ```
 
+## Running process if test succeeds or fails
+
+We can use the following structure to run a process if a test condition obtains:
+
+```bash
+[[ -d ~ ]] && echo "/home is a directory"
+```
+
 ## Extended test: `[[...]]`
 
 When we use **double brackets** we are using _extended_ `test`.
@@ -72,6 +81,16 @@ The extended test supports the standard `test` comparisons and adds other featur
   [[ -d ~ || -a /bin/mash ]]; echo $?
   ```
 
+### Using regular expressions
+
+Extended test also allows us to use regular expressions as part of our test conditions. In order to test against a regular expression we use `=~` as the comparison operator.
+
+```bash
+[[ "thomas" =~ t.* ]]; echo $?
+```
+
+Here the test succeeds because "thomas" begins with "t" followed by any other character.
+
 ## Further examples
 
 **Test if a character exists in two strings**

Programming_Languages/Shell/Text_manipulation.md

@@ -5,6 +5,8 @@ tags:
   - shell
 ---
 
+# Text manipulation
+
 ## Sorting strings: `sort`
 
 If you have a `.txt` file containing text strings, each on a new line you can use the sort function to quickly put them in alphabetical order: