update

Bash-Scripting.txt

@@ -193,3 +193,108 @@
 
     We can exit script using exit command.
     exit command can be used with number 0 - 255.
+
+-> If Statement
+
+    if[ condition ]; then
+        ....
+    elif[ condition ]; then
+        ....
+    elif[ condition ]; then
+        ....
+    else
+        ....
+    fi
+
+    * AND with if statement ?
+
+    if[ condition ] && [ condition ]; then
+        ....
+    fi
+
+    * OR wiht if statement ?
+
+    if[ condition ] || [ condition ]; then
+        ....
+    fi
+
+    * Negate if condition
+
+    if[ !condition ]; then
+        ....
+    fi
+
+    if![ condition ]; then
+        ....
+    fi
+
+-> Mathematical comparison:
+
+    * Operands
+
+        $ -eq   equal to
+        $ -ne   not equal to
+        $ -gt   greater than
+        $ -lt   less than
+        $ -ge   greater than or equal to
+        $ -le   less than or equal to
+
+    Examples:
+
+        if [ $VAR -eq 5 ]; then
+        if [ $VAR -gt 7 ]; then
+        if [ $VAR -eq 5 ] && [ $COUNT -ne 1 ]; then
+
+
+
+-> String Comaparison
+
+    * Comapare two strings
+    [ "$STR1" = "$STR2" ]
+    [ "$STR1" != "$STR2" ]
+
+    [ "$STR1" = "hello" ]
+    [ "$STR1" != "hello" ]
+
+    * Compare two strings - quotation marks?
+      Bash can handle it in another way [[ ]]
+
+      [[ $STR1 = $STR2 ]]
+      [[ $STR1 != $STR2 ]]
+
+      [[ $STR1 = "hello" ]]
+      [[ $STR1  != "hello ]]
+
+      This is not widely used and most scripts
+      are using quotation marks with single 
+      brackets
+
+    * Test if string is empty
+
+        [ -z "$STR1" ] returns true if STR1 holds
+                        an empty string
+
+        [[ -z $STR1 ]] possible, but not widely used
+        
+        [ -n "$STR1" ] returns true if STR1 holds
+                        a non-empty string
+
+        [[ -n $STR1 ]] possible, but not widely used
+
+    * Alphabetically compare two strings
+
+    [[ $STR1 > $STR2 ]]
+
+    [[ $STR1 < $STR2 ]]
+
+    No choice!!!
+
+    * Wildcards
+
+        [[ $STR1 == string-with-wildcards ]]
+
+    * Regular expression
+
+        [[ $STR1 =~ $regex ]]
+
+