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+====== For sample ======
+<code>
+#!/bin/bash
+for i in $( ls ); do
+  echo item: $i
+done
+</code>
+====== C-like for ======
+<code>
+#!/bin/bash
+for i in `seq 1 10`;
+do
+  echo $i
+done
+</code>
+====== While sample ======
+<code>
+#!/bin/bash
+COUNTER=0
+while [  $COUNTER -lt 10 ]; do
+  echo The counter is $COUNTER
+  let COUNTER=COUNTER+1
+done
+</code>
+<code>
+#!/bin/bash
+var0=0
+LIMIT=10
+while [ "$var0" -lt "$LIMIT" ]
+#      ^                    ^
+# Spaces, because these are "test-brackets" . . .
+do
+  echo -n "$var0 "        # -n suppresses newline.
+  #             ^           Space, to separate printed out numbers.
+  var0=`expr $var0 + 1`   # var0=$(($var0+1))  also works.
+                          # var0=$((var0 + 1)) also works.
+                          # let "var0 += 1"    also works.
+done                      # Various other methods also work.
+echo
+exit 0
+</code>
+<code>
+#!/bin/bash
+echo
+                               # Equivalent to:
+while [ "$var1" != "end" ]     # while test "$var1" != "end"
+do
+  echo "Input variable #1 (end to exit) "
+  read var1                    # Not 'read $var1' (why?).
+  echo "variable #1 = $var1"   # Need quotes because of "#" . . .
+  # If input is 'end', echoes it here.
+  # Does not test for termination condition until top of loop.
+  echo
+done
+exit 0
+</code>
+Inside its test brackets, a while loop can call a function:
+<code>
+t=0
+condition ()
+{
+  ((t++))
+  if [ $t -lt 5 ]
+  then
+    return 0  # true
+  else
+    return 1  # false
+  fi
+}
+while condition
+#     ^^^^^^^^^
+#     Function call -- four loop iterations.
+do
+  echo "Still going: t = $t"
+done
+# Still going: t = 1
+# Still going: t = 2
+# Still going: t = 3
+# Still going: t = 4
+</code>
+====== Until sample ======
+<code>
+#!/bin/bash
+COUNTER=20
+until [  $COUNTER -lt 10 ]; do
+  echo COUNTER $COUNTER
+  let COUNTER-=1
+done
+</code>
+====== Snow in Terminal ======
+<code>
+while true
+  do
+  N=$(($RANDOM % $COLUMNS))
+  for i in $( seq 1 $N )
+    do
+    echo -n " "
+    done
+    echo \*
+  done
+</code>
+And as a one-liner:
+<code>while true;do N=$(($RANDOM % $COLUMNS));for i in $( seq 1 $N );do echo -n " ";done;echo \*;done</code>
+----
+Source: http://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO-7.html