how to jump back to line in bash script?-CodePudding

i have "if" loop and want that in my "then" part the command will be "jump back to line...and run the script all over from that line". how do I write it

if [ -s file.txt ] 
then
    jump to command \ jump to line ....
else 
    <command> 
fi

thanks

CodePudding user response：

How to avoid goto and start processing from a certain point? As an example you want to start over the processing until a flag has value 5.
The comments mentioned a loop. A dirty loop is something like this:

startfrom=0
flag=0
# Dirty loop, look to second code fragment for cleanup
while :; do
  if ((startfrom==0)); then
   echo "First time, all statements"
   ((startfrom  ))
  fi
  if ((startfrom==1)); then
    echo "Starting from line labelled 1"
    ((startfrom  ))
    ((flag  ))
  fi
  echo "Flag=$flag"
  if ((flag<5)); then
    echo "Simulating goto line labelled 1"
    startfrom=1
    continue
  fi
  echo "The End"
  break
done

Before you think "Ok, that is the goto I wanted. What a load of overhead you need in bash", look at the second implementation.

process_flag() {
  ((flag  ))
  echo "Flag=$flag"
  if ((flag<5)); then
    echo "Need to process again"
    return 0
  fi
  return 1
}

flag=0
echo "First time, all statements"
while :; do
  process_flag || break
done
echo "The End"

This already looks better. When the function is small, you can put everything in the loop.

flag=0
echo "First time, all statements"
while :; do
  ((flag  ))
  echo "Flag=$flag"
  if ((flag<5)); then
    echo "Need to process again"
    continue
  else
    break
  fi
done
echo "The End"

Is this example you can use a different loop. Before writing statements for each step, look at the structure and think what control functions you need. Perhaps you want a simple

echo "First time, all statements"
for ((flag=1; flag<=5; flag  )); do
  echo "Flag=$flag"
  if ((flag<5)); then
    echo "Need to process again"
  fi
done
echo "The End"

When your loop has more lines than your screen, consider using a function for the small details.

CodePudding user response：

(Note: this is a terrible idea)

The shell doesn't give you a goto, but you can fabricate one!

#!/bin/bash

echo executing before label

# label:

goto() {
    target="$1"
    shift
    exec sh -c "$(sed -e "1,/^# $target:$/d" $0)" "$0" "$@"
}

echo executing from label args: $@

if test "$1" = 5; then
    shift
    goto label "$@"
fi

Seriously, don't do this.