Shell脚本中变量的范围

Question

I am new to shell scripting. My aim is to print the numbers like 01, 02, 03...09 if the user enters 1,2,3,4...9 (less than 10). I wrote the below code but lst line print the value is of only single digit.

issuehour()
{
  issue_hour="$1";

  if [ $issue_hour -lt 10 ] then 
    h="0"$issue_hour
    return $h
  else
    #echo "less than 10"
    return "$1"
  fi
}

echo "enter hour"
read hour
hr=$(issuehour "$hour")
echo "after calling function:-" $hr

Answer 1

Return statement in bash is synonymous to exit code and ranges from 0 - 255.

"Echo" is used to return value / output the value of the function. This should be captured by the calling function using $( ) similar to hr=$(issuehour "$hour") that you have used.

Coming to your question, without the echo statement, the function did not return any value to the calling function and that explains why you did not get the desired output. However, since you have used "return", that would have been considered as the ' return code of the function '. To verify this, try:

function issuehour()
{
  issue_hour="$1";

  if [[ $issue_hour -lt 10 ]]
  then
    h="0"$issue_hour
    return $h
  else
    #echo "less than 10"
    return "$1"
  fi
}

echo "enter hour"
read hour
hr=$(issuehour "$hour")
echo $?

This will give the same result you were looking for.

PS: It is better to follow the conventional method of using "echo" to return value of the function and "return" statement for "return code"

Answer 2

Just use printf with 0 padding:

printf "%02d\n" 1
01
printf "%02d\n" 2
02
printf "%02d\n" 9
09
printf "%02d\n" 10
10

Answer 3

You can use the following code.

issuehour()
{
  issue_hour="$1";

  if [ $issue_hour -lt 10 ] ;then
    h="0"$issue_hour
    echo $h
  else
    #echo "less than 10"
    echo "$1"
  fi
}

echo "enter hour"
read hour
hr=$(issuehour "$hour")
echo "after calling function:-" $hr

return command will return the exit status of a function , Instead you can use echo command.

[root@server1 tmp]# bash new
enter hour
10
after calling function:- 10
[root@server1 tmp]# bash new
enter hour
1
after calling function:- 01