bash log and execute function

ninj4fly · 09-18-2008, 06:58 PM

Hi,

I have to write bash function that logs the commands before executing them. I try:

function log_and_exec () { logger -p local5.info $@ && $@; }

but it is not working as I expected. When the actual command contains "|" (pipe) for example, what I found in the log file is only that part of the command preceding the "|" character although the entire command is executed.

For example: log_and_exec uptime | grep -o users
logs only the word uptime. Another example using "&&" is:

log_and_exec uptime && date
Again only uptime is logged, both commands are executed. The same behavior when using "echo" instead of "logger".

Any help would be greatly appreciated.

chrism01 · 09-18-2008, 07:48 PM

Try saving $@ in a another temp var first, then escape any special chars, then pass $temp to the logger.
Call the orig version of the cmd afterwards.

Mr. C. · 09-19-2008, 12:25 AM

The function will never see the pipe or any redirection, as the shell parses and removes them before the function is called, unless they are quoted.

ninj4fly · 09-20-2008, 04:35 AM

Thanks for your answers.

@chrism01 Saving the command in $temp did not help. I tried:
temp=`echo "$@" | sed -e 's/[|&]/\\&/g'` and logger $temp. The overall effect is exactly as logging "$@", only the part left to these characters is logged.

@Mr. C. It seems you are right.

i92guboj · 09-20-2008, 05:39 AM

Quote:

Originally Posted by Mr. C.

The function will never see the pipe or any redirection, as the shell parses and removes them before the function is called, unless they are quoted.

That's right. Bash will consume the pipe or any other similar special character before your function can read it. You could use an alternate character for redirection or a command line modifier, or pass it scaped to the function so it can see it. Of course that will require some extra work so the function can parse all the stuff and do what's adequate on each case, I hope you get the idea.

Mr. C. · 09-20-2008, 10:31 AM

Create your function like this:

Code:

# Execute command line first, and then log and include 
# status of last command in pipeline.
# To obtain the exit status of each command in any pipeline,
# use the bash PIPESTATUS array in your logger function
# instead of $?.

function log_and_exec () {
    eval "$@"
    echo logger -p local5.info \[$?\] "$@"
}

Call your function with quotes like this:

Code:

log_and_exec 'echo Hello World | cat -n'

If you need to interpolate a variable into the call first, use double quotes:

Code:

log_and_exec "echo I am $USER | perl -pe 's/(\w+)$/\u\$1/'"