Différences

Ci-dessous, les différences entre deux révisions de la page.

--- tech:bash_scripts [2024/10/25] – créée Mathieu
+++ tech:bash_scripts [2025/04/12] (Version actuelle) – supprimée Mathieu
@@ Ligne 1: / Ligne 1: @@
-====== Bash Scripting ======
-===== Table of Contents =====
-  * [[#basics|Basics]]
-    * [[#exit_codes|Exit codes]]
-    * [[#variables_and_data_types|Variables and Data Types]]
-    * [[#command_substitution|Command substitution]]
-    * [[#input_output_redirection|Input/output redirection]]
-  * [[#control_structures|Control Structures]]
-    * [[#conditionals|Conditionals]]
-      * [[#if_statements|If statements]]
-      * [[#case_statements|Case statements]]
-    * [[#loops|Loops]]
-      * [[#for_loops|For loops]]
-      * [[#while_loops|While loops]]
-    * [[#functions|Functions]]
-  * [[#comparisons_and_tests|Comparisons and Tests]]
-    * [[#string_comparison|String comparison]]
-    * [[#numerical_comparison|Numerical comparison]]
-    * [[#variable_existence|Variable existence]]
-    * [[#file_checks|File checks]]
-    * [[#permissions_checks|Permissions checks]]
-  * [[#logical_operations_and_combinations|Logical Operations and Combinations]]
-    * [[#internal_combinations|Internal combinations]]
-    * [[#external_combinations|External combinations]]
-    * [[#conditional_execution|Conditional execution]]
-  * [[#useful_commands_and_concepts|Useful Commands and Concepts]]
-    * [[#sleep|sleep]]
-    * [[#read|read]]
-    * [[#set_options|set options]]
-    * [[#mktemp|mktemp]]
-    * [[#trap|trap]]
-    * [[#arrays|Arrays]]
-  * [[#best_practices|Best Practices]]
-===== Basics =====
-==== Exit codes ====
-In bash, exit codes indicate the success or failure of a command or script.
-  * 0 -> success
-  * anything else -> failure
-==== Variables and Data Types ====
-Bash primarily deals with strings, but can handle numbers and arrays.
-Example:
-<code bash>
-name="John"
-age=30
-</code>
-==== Command substitution ====
-Allows you to use the output of a command as part of another command.
-Example:
-<code bash>
-current_date=$(date +%Y-%m-%d)
-</code>
-==== Input/output redirection ====
-Allows you to control where input comes from and where output goes.
-Example:
-<code bash>
-echo "Hello" > output.txt  # Redirect output to a file
-cat < input.txt            # Read input from a file
-</code>
-===== Control Structures =====
-==== Conditionals ====
-=== If statements ===
-Used for conditional execution of code.
-Example:
-<code bash>
-if [[ condition ]]; then
-  echo "condition met"
-elif [[ condition_2 ]]; then
-  echo "condition_2 met"
-else
-  echo "no condition met"
-fi
-</code>
-=== Case statements ===
-Used for multiple conditional branches.
-Example:
-<code bash>
-case "$variable" in
-  pattern1) command1 ;;
-  pattern2) command2 ;;
-  *) default_command ;;
-esac
-</code>
-==== Loops ====
-=== For loops ===
-Used to iterate over a list of items.
-Examples:
-<code bash>
-# Regular
-my_array=(1 2 3 4 5)
-for item in ${my_array[@]}
-do
-  echo $item
-done
-# C-style
-for ((i = 0; i < 10; i++)); do
-  echo "$i"
-done
-# Range
-for i in {1..10}; do
-  echo "$i"
-done
-# Pattern matching
-for item in ./content/*.md; do
-  echo "$item"
-done
-# Command result
-for item in $(ls ~/Notes/); do
-  echo $item
-done
-</code>
-=== While loops ===
-Executes a block of code as long as a condition is true.
-Example:
-<code bash>
-counter=0
-while [[ $counter -lt 5 ]]; do
-  echo $counter
-  ((counter++))
-done
-</code>
-==== Functions ====
-Reusable blocks of code. They operate like mini-scripts.
-Example:
-<code bash>
-greet() {
-  echo "Hello, $1!"
-}
-greet "World"
-</code>
-===== Comparisons and Tests =====
-==== String comparison ====
-<code bash>
-val="a"
-[[ "$val" == "a" ]]
-[[ "$val" != "b" ]]
-</code>
-==== Numerical comparison ====
-<code bash>
-num=1
-[[ "$num" -eq 1 ]]  # equal
-[[ "$num" -ne 2 ]]  # not equal
-[[ "$num" -lt 2 ]]  # less than
-[[ "$num" -le 2 ]]  # less than or equal
-[[ "$num" -gt 1 ]]  # greater than
-[[ "$num" -ge 1 ]]  # greater than or equal
-</code>
-==== Variable existence ====
-<code bash>
-val=""
-[[ -z $val ]]  # var is null
-[[ -n $val ]]  # var is not null
-</code>
-==== File checks ====
-<code bash>
-file="./hello"
-[[ -f $file ]]  # file exists
-[[ -d $file ]]  # directory exists
-[[ -e $file ]]  # file or directory exists
-</code>
-==== Permissions checks ====
-<code bash>
-file="./hello"
-[[ -r $file ]]  # readable
-[[ -w $file ]]  # writable
-[[ -x $file ]]  # executable
-</code>
-===== Logical Operations and Combinations =====
-==== Internal combinations ====
-<code bash>
-[[ $val -gt 5 -a $val -lt 10 ]]  # -a -> AND
-[[ $val -gt 5 -o $val -lt 3 ]]   # -o -> OR
-</code>
-==== External combinations ====
-<code bash>
-[[ $val -gt 5 ]] && [[ $val -lt 10 ]]  # AND
-[[ $val -gt 5 ]] || [[ $val -lt 3 ]]   # OR
-</code>
-==== Conditional execution ====
-<code bash>
-command1 && command2  # Execute command2 if command1 was successful
-command1 || command2  # Execute command2 if command1 failed
-</code>
-===== Useful Commands and Concepts =====
-==== sleep ====
-Pauses the script for a specified amount of time.
-==== read ====
-Reads input from the user.
-Example:
-<code bash>
-read -p "Do you want to continue (Y/n) " resp
-if [[ $resp != "Y" ]]; then
-  exit 1
-fi
-echo "Continuing..."
-</code>
-==== set options ====
-Activates strict mode in bash:
-<code bash>
-set -euo pipefail
-</code>
-  * set -e: exit on error
-  * set -u: exit on unset var
-  * set -o pipefail: exit on pipe fail
-==== mktemp ====
-Creates a temporary file or directory.
-==== trap ====
-Sets up a function to be called when the script receives specific signals.
-==== Arrays ====
-Store multiple values in a single variable.
-Example:
-<code bash>
-fruits=("apple" "banana" "cherry")
-echo ${fruits[0]}  # Outputs: apple
-</code>
-===== Best Practices =====
-  * Use meaningful variable names
-  * Comment your code
-  * Use functions for repeated code
-  * Always quote variables when using them
-  * Use set -euo pipefail for safer scripts