Shell – Pass multiple command line arguments to an executable with text files

command lineshell-script

I have a C executable that takes in 4 command line arguments.

program <arg1> <arg2> <arg3> <arg4>

I'd like to create a shell script that continually runs the executable with arguments supplied by text files. The idea would be something like this:

./program "$(< arg1.txt)" "$(< arg2.txt)" "$(< arg3.txt)" "$(< arg4.txt)"

Where the arguments supplied for run n would be on line n of each of the files. When I tried doing this, the printf() calls were interfering with each other or some other funny business was going on. I would also be open to a script that takes only one file where the arguments are delimited in some way.

Best Answer

while 
  IFS= read -r a1 <&3 &&
    IFS= read -r a2 <&4 &&
    IFS= read -r a3 <&5 &&
    IFS= read -r a4 <&6
do
  ./program "$a1" "$a2" "$a3" "$a4" 3<&- 4<&- 5<&- 6<&-
done 3< arg1.txt 4< arg2.txt 5< arg3.txt 6< arg4.txt

That runs the loop until one of the files is exhausted. Replace the &&s with ||s to run it until all the files are exhausted instead (using empty arguments for shorter files).

With GNU xargs, you could also do:

paste -d '\n' arg[1-4].txt | xargs -n 4 -r -d '\n' ./program

(though beware ./program's stdin would then be /dev/null)

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Shell Script – How to Concatenate Lines from Two Text Files

If you really want to do it in bash, I'd suggest making use of the -u fd option to read from the two files simultaneously using numbered streams, e.g.

while read -r -u3 product; read -r -u4 comp; do 
  printf '%s;%s\n' "$product" "$comp"
done 3<products.txt 4<comps.txt

However, you could just use the paste utility

paste -d\; products.txt comps.txt

Shell – How to log calls using a wrapper script when there are multiple symlinks to the executable

You often see this in case of utilities like busybox, a program that can provide most of the common unix utilities in one executable, that behaves different depending on its invocation/ busybox can do a whole lot of functions, acpid through zcat.

And it commonly decides what it's supposed to be doing by looking at it's argv[0] parameter to main(). And that shouldn't be a simple comparison. Because argv[0] might be something like sleep, or it might be /bin/sleep and it should decide to do the same thing. In other words, the path is going to make things more complex.

So if things were done by the worker program right, your logging wrapper could execute from something like /bin/realstuff/make_tea and if the worker looks at argv[0] basename only, then the right function should execute.

#!/bin/sh -
myexec=/tmp/MYEXEC$$
mybase=`basename -- "$0"`

echo "$0 $@" >> logfile

mkdir "$myexec" || exit
ln -fs /usr/bin/real/do_stuff "$myexec/$mybase" || exit
"$myexec/$mybase" "$@"
ret=$?
rm -rf "$myexec"
exit "$ret"

In the example above, argv[0] should read something like /tmp/MYEXEC4321/make_tea (if 4321 was the PID for the /bin/sh that ran)which should trigger the basename make_tea behavior

If you want argv[0] to be an exact copy of what it would be without the wrapper, you have a tougher problem. Because of absolute file paths beginning with /. You can't make a new /bin/sleep (absent chroot and I don't think you want to go there). As you note, you could do that with some flavor of exec(), but it wouldn't be a shell wrapper.

Have you considered using an alias to hit the logger and then start the base program instead of a script wrapper? It'd only catch a limited set of events, but maybe those are the only events you care about

Best Answer

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