Shell Scripting – How to Avoid Tempfiles in Shell Programming

kshscriptingshell

I often write KSH shell scripts that follow the same pattern:

  • (1) retrieve output from one or more command
  • (2) format it using grep|cut|awk|sed and print it to the screen or to a file

In order to do that, I often store the output of (1) in a tempfile, and then do the formatting in (2) on that file.

Take that code for instance: 

TMPFILE=file.tmp

# If tmpfile exists rm it.
[ -f $TMPFILE ] && rm -f $TMPFILE

for SERVICE in $(myfunc); do
    getInfo $SERVICE > $TMPFILE # Store raw output in the TMPFILE

    # I retrieve the relevant data from the TMPFILE
    SERV_NAME=$(head -1 $TMPFILE | sed -e 's/ $//')
    SERV_HOSTNAME=$(grep HOSTNAME $TMPFILE | cut -d "=" -f2)
    SERV_ARGS=$(grep Arguments $TMPFILE | cut -d ":" -f2)

    print $SERV_NAME $SEP $SERV_HOSTNAME $SEP $SERV_ARGS
    rm -f $TMPFILE #rm the TMPFILE in vue of next iteration
done

Is there a way, using pipes, redirections and whatnots, to avoid writing a file to disk each time?

If it helps, I'm using ksh Version M-11/16/88i

Best Answer

Your code looks like an entirely justified example of using tempfiles to me. I'd stay: stick with this approach. The only thing that really needs to be changed is the way you create the tempfile. Use something like

 TMP=$(tempfile)

or

 TMP=$(mktemp)

or at least

 TMP=/tmp/myscript_$$

This way you won't let the name be easily predicted (security) and out rule interference between several instances of the script running at the same time.

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