running total in unix shell script

Question

I'm having some issues in a unix shell script I'm trying to write that keeps a running total of the number of lines in multiple files from the command line. I can count the lines individually and display them for each run through the loop but my lines variable always reads 0 at the end.

#! /bin/sh
lines=0

line_count(){
    #count the lines
    l= blablabla.....
    lines=`lines + l`
}

for f in "$@"
do
echo "total lines:"
( line_count "$f" )
done

You just want sh or you don't have access to wc, How about grep -c '.*' — Chris Seymour
– Chris Seymour, Commented Nov 30, 2012 at 12:51
I have the script how I want it, I just don't understand this whole sub shell thing that I believe is the cause of my counter not keeping track like it should. — Matthew The Terrible
– Matthew The Terrible, Commented Nov 30, 2012 at 12:53

Anders Johansson · Accepted Answer · 2012-11-30 13:39:24Z

3

If you run something in a subshell, any variable changes you do (e.g. increasing $lines) are only valid within that subshell and are lost when the subshell exits. But since you are using a function you don't need a subshell at all, just call the function.

Also lines=`lines + l` will try to execute the command lines with arguments + and l, which I think is not what you intended. To evaluate the result of an expression, use the $(( ... )) syntax, and prepend $ to your variables to work with their values.

Finally you never use the value of $lines, you may want to print it after you've called the function.

#! /bin/sh
lines=0

line_count(){
    #count the lines
    l= blablabla.....
    lines=$(( $lines + $l ))
}

for f in "$@"
do
    line_count "$f"
    echo "total lines: $lines"
done

answered Nov 30, 2012 at 13:39

Anders Johansson

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2 Comments

Matthew The Terrible Over a year ago

Would it be bad to just save the running total to a file and then grab the values out of there when I need them? Is that bad practice?

Anders Johansson Over a year ago

@jimjohnjim, it can be done that way but it would be much more efficient to keep the data in memory, especially for cases like this where you store a single number. For more complex tasks it may be necessary or helpful to write partial results to file for use later.

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