我如何使命令成为变量

Question

A relative newbie here. I'm reading in a file using the following commands:

while read line
 do 
      commands here
done < file

I'm splitting the line into two parts separated by a dash by the following

dash_pos=`expr index "$line" -`

dash_pos is obviously not a constant that's why I make it a variable.

I can now do the following

Part1=${line:0:$dash_pos -2}
Part2=${line:$dash_pos + 1}

These commands work as expected.

Is there a way that I can make the string manipulation commands a variable eg

Find_Part1=${line:0:$dash_pos -2}
Find_Part2=${line:$dash_pos + 1}

so that

  Part1=$Find_Part1  &   Part2=$Find_Part2

work as before, but it will then allow me to do

 Part1=$Find_Part2   &   Part2=$Find_Part1

when necessary.

Any help will be appreciated as I have tried quotes, double quotes, brackets, curly brackets and back ticks in a variety of combinations to try and get this to work. John

Answer 1

Storing executable code in a variable is far more trouble than it is worth. Use functions instead:

Find_Part1 () {
    printf "%s" "${line:0:$dash_pos -2}"
}

Find_Part2 () {
    printf "%s" "${line:$dash_pos + 1}"
}

Part1=$(Find_Part1)
Part2=$(Find_Part2)

It appears, though, that what you really want is something along the lines of

while IFS="-" read Part1 Part2; do
   ...
done < file

to let the read command split line into Part1 and Part2 for you.

Answer 2

It is unclear why you cannot just do what is literally in the question:

# get the parts
Find_Part1=${line:0:$dash_pos -2}
Find_Part2=${line:$dash_pos + 1}

# ... as necessary:

if such and such condition ; then
   Part1=$Find_Part1
   Part2-$Find_Part2
else
   Part1=$Find_Part2
   Part2=$Find_Part1
fi

Also, you can instead exchange the values of Part1 and Part2 when necessary, requiring only one temporary variable

if interesting condition ; then
    temp=$Part1; Part1=$Part2; Part2=$temp
fi

Inside a Bash function, we would might make temp a local to avoid name clashes and namespace clutter:

local temp