Is There a "Goto" Statement in Bash

Is there a goto statement in bash?

No, there is not; see §3.2.4 "Compound Commands" in the Bash Reference Manual for information about the control structures that do exist. In particular, note the mention of break and continue, which aren't as flexible as goto, but are more flexible in Bash than in some languages, and may help you achieve what you want. (Whatever it is that you want . . .)

How to use goto statement in shell script

As others have noted, there's no goto in bash (or other POSIX-like shells) - other, more flexible flow-control constructs take its place.

Look for heading Compound Commands in man bash.

In your case, the select command is the right choice.
Since how to use it may not be obvious, here's something to get you started:

#!/usr/bin/env bash

echo "Main Menu"

# Define the choices to present to the user, which will be
# presented line by line, prefixed by a sequential number
# (E.g., '1) copy', ...)
choices=( 'copy' 'exit' )

# Present the choices.
# The user chooses by entering the *number* before the desired choice.
select choice in "${choices[@]}"; do

  # If an invalid number was chosen, $choice will be empty.
  # Report an error and prompt again.
  [[ -n $choice ]] || { echo "Invalid choice." >&2; continue; }

  # Examine the choice.
  # Note that it is the choice string itself, not its number
  # that is reported in $choice.
  case $choice in
    copy)
      echo "Copying..."
      # Set flag here, or call function, ...
      ;;
    exit)
      echo "Exiting. "
      exit 0
  esac

  # Getting here means that a valid choice was made,
  # so break out of the select statement and continue below,
  # if desired.
  # Note that without an explicit break (or exit) statement, 
  # bash will continue to prompt.
  break

done

Skip (goto) a piece of code in bash?

No, there isn't.

But this example doesn't need it:

read -p "WAN1 exists?: " -n 1 -r
if [[ $REPLY =~ ^[Yy]$ ]]; then
  # WAN1
  read -p "Enter WAN1 IP: " wan1
  if [[ $wan1 =~ ^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$ ]]; then
    sed -i~ -e "s/bizip/$wan1/g" test.txt
  else
    echo Error
  fi
fi
# WAN2_prompt
read -p "WAN2 exists?: " -n 1 -r
if [[ $REPLY =~ ^[Yy]$ ]]; then
  read -p "Enter WAN2 IP: " wan2
  if [[ $wan2 =~ ^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$ ]]; then
    sed -i~ -e "s/bizip/$wan2/g" test.txt
  else
    echo Error
  fi
fi
# ...

Goto beginning of if statement?

You have to use a loop; bash doesn't have a goto statement.

while true; do
  # set the value of INPUT here
  if [ "$INPUT" = "no" ]; then
    Do something
  elif [ "$INPUT" = "yes" ]; then
    Do something else
  else
    echo "Input not understood"
    continue
  fi
  break
done

In this "infinite" loop, we use the continue statement in the else clause to return to the top of the loop, where we do something to get a new value of INPUT. If we don't execute the else clause, we hit the break statement, which exits the loop.

how do you goto in mac shell (like a in windows .bat)?

There's actually no exact replacement. In bash programming, you can define functions, so you might do something like

one() {
    # Some stuff
    two
}

two() {
    # Some more stuff
    one
}

Although eventually that'll run out of stack space; hopefully there's some circumstances under which you'll include code to stop the recursion. I realize this is just a straw man example, but bash would let you use other forms of loops here which would work better; for example:

while true
do
    # Some stuff
    # Some more stuff
done

What could be the substitute to handle the flow control of go-to in SHELL script

Rather than trying to extend the syntax of the shell to do

start:

for ...; do
    for ...; do
        ...
    done
done

if CONDITION; then
    goto start
else
    SOMETHING
fi

you may do

while true; do
    for ...; do
        for ...; do
            ...
        done
    done

    if ! CONDITION; then
        SOMETHING
        break
    fi
done

or

while true; do
    for ...; do
        for ...; do
            ...
        done
    done

    if ! CONDITION; then
        break
    fi
done

SOMETHING

UPDATE: New code in question:

start:
while true; do
    for ...; do
        for ...; do
            if ...; then
                break 99
            fi
            ...
        done
    done
done

...

if CONDITION; then
    SOMETHING
    goto start
else
    SOMETHING_ELSE
fi

for ...; do
    ...
done

To avoid a goto, this may be transformed into

while true; do
    while true; do
        for ...; do
            for ...; do
                if ...; then
                    break 99   # change to one less than
                               # the total depth, to not exit
                               # outermost loop
                fi
                ...
            done
        done
    done

    ...

    if ! CONDITION; then
        break
    fi

    SOMETHING
done

SOMETHING_ELSE

for ...; do
    ...
done

Something similar to goto on linux

Bourne shells like sh and bash don't have GOTO statements. It's considered harmful.

Instead, use structured flow control like if statements:

echo "Enter the number to divide (dividend) (enter 999 to quit):"
read numberOne
if [ "$numberOne" -ne 999 ]
then
  echo "Enter the number to divide (divisor) (enter 999 to quit):"
  read numberTwo

  while [ "$numberOne" -ne '999' ] && [ "$numberTwo" -ne '999' ]
  do
      while [ "$numberTwo" -eq 0 ]
      do
      echo "You cannot divide by 0, please enter another number:"
      read numberTwo
      done

      RESULT=$(echo "$numberOne/$numberTwo" | bc -l)
      echo $numberOne / $numberTwo = $RESULT
      echo $numberOne / $numberTwo = $RESULT >> results.txt
      echo "Enter the number to divide (dividend) (enter 999 to quit):"
      read numberOne
      if [ "$numberOne" -ne 999 ]
      then
          echo "Enter the number to divide (divisor) (enter 999 to quit):"
          read numberTwo
      fi
  done
fi

counter=1
totalCount=0
temporal=0

while [ "$counter" -lt '101' ]
do
    temporal=$( expr $counter % 5)
    echo $counter MOD 5 = $temporal
    echo $counter MOD 5 = $temporal >> results.txt
    totalCount=$(echo "$totalCount+$temporal" | bc -l)
    counter=$(echo "$counter+1" | bc -l)
done

average=$(echo "$totalCount/100" | bc -l)
echo The average of all the MODs is $average >> results.txt

It may seem more awkward than one simple goto, but as you take advantage of more structured control flow, the code gets easier to read and follow:

readNumber() {
  local number
  read -p "$1" number
  [ "$number" -ne 999 ] && echo "$number"
}

while one=$(readNumber "Enter dividend or 999 to quit: ") && \
      two=$(readNumber "Enter divisor or 999 to quit: ")
do
    echo "$one / $two = $(echo "$one / $two" | bc -l)" | tee results.txt
done

This keeps asking for numbers to divide, until the user enters 999 for either of them.

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