Standard Output for script

[WhiskyChris]

I have a short script for which I want it to either output to the terminal it's being run in ("standard out") or to a log file depending on the condition of a flag. If I call "report.sh" it should run (and output) in the terminal, if I call "report.sh -q" it should send its output to log files.

At the moment I am using getopts (Linux.com :: Parsing arguments for your shell script) to parse the flags so that if -q is specified the variable quiet=1 and I have a conditional statement for if [ "quiet" ] then OUT=$logfile, else OUT=$standardoutput. For each subsequent command I then direct its output towards $OUT.

My problem is that I don't know what to set $OUT to for when I want it "sent" to standard out, and also something is screaming at me that there should be a simpler way to do this. My script as it stands is below, any suggestions?

#!/bin/bash
#
# This file generates reports on the status
# of running jobs on various servers
#

# Location of log files
OLD=$HOME/tmp/jobStatus.old
NEW=$HOME/tmp/jobStatus.new

# Parse arguments
quiet=
while getopts 'q' OPTION
do
   case $OPTION in
   q)  quiet=1
               ;;
   ?)  echo    "Usage: $(basename $0) [-q for quiet output)]" >&2
               exit 2
               ;;
   esac
done
shift $(($OPTIND - 1))

# If quiet, setup log file output
if [ "quiet" ]; then 
   if [ -a $OLD ]; then rm $OLD ; fi
   if [ -a $NEW ]; then mv $NEW $OLD ; fi
   OUT=$NEW
else
   OUT="??? - standard out"
fi

# Main body of script
user=username
servers=(server01 server02 server03)

date +%d/%m/%y\ %R > $OUT
for i in ${servers[@]}; do
  ssh -l $user ${i} "~/bin/running -c" >> $OUT
done

[fiomba]

Hi,
I'm not an expert, but after many years, you learn something...
The outputs are two: the standard one (the screen) and the error output (normally it too using the screen).
The 1st is "automatically" directed to screen and you need no action except printing or echoing (if you use bash) the data you want.
The output of any program that accesses the screen can be redirected to a file and visualized
by a text or a graphic editor by the well known

executable (options) command_object > file_capturing_output
for ex. ls -1 MyDir > myDir_FileList.txt

As you see you don't have to modify the source of the command ls (probably a c program)...
The same thing is valid also for logging.

The redirection captures also the error output. Such a thing is sometime annoying.
For example try to use find outside of the home...
In such a case I use the redirection of error to null...

find /usr -name "*xx*" 2>/dev/null

In this way you don't see the annoying "access denied"...
As a conclusion I would write a script with no options for output... you decide what you want
by running with or without redirection to a file or a log file.
Bye

[WhiskyChris]

Thanks fiomba, I believe I understand what you are saying but I shall try to rephrase my question in response...

I would like my script either to output to the screen or to a log file. From what you are saying I would do this simply by calling the script by it's name or by appending "> logfile" after calling it which I understand. The complication is the management of the logfiles.

If I want the script to output to log files the idea is to maintain two files - the current output "jobStatus.new" and the previous output "jobStatus.old" which I will then subsequently examine with diff to determine any changes (I'm learning a bit of awk at the moment as well!). To do this I currently use the log management section to shuffle the log files, however I don't need to do this if I output to the screen.

I guess I could do something like...

if [ "quiet" ]; then
   date +%d/%m/%y\ %R > $OUT
   for i in ${servers[@]}; do
       ssh -l $user ${i} "~/bin/running -c" >> $OUT
   done
else
   date +%d/%m/%y\ %R
   for i in ${servers[@]}; do
      ssh -l $user ${i} "~/bin/running -c"
   done
fi

...but it would be ideal if I could use $OUT for either screen or file output.

[matonb]

Maybe this previous post will help...
redirecting BASH script stdout/stderr from the script itself - LinuxQuestions.org

[lomcevak]

The "standard out" is a device called /dev/stdout. So assign your variable to it:

OUT=/dev/stdout

[WhiskyChris]

Excellent, that's what I was looking for lomcevak - knew it had to be something simple. I've already tweaked the file now though however and gone with earlier suggestions of just sending output to file from calling the script.

Thanks all the same.

[matonb]

Glad you've found what you wanted

I must admit that I do like colucix's solution from the earlier posting

#!/bin/bash
logfile=$$.log
exec > $logfile 2>&1

As it gives you an easy way to output to either a log file, stdout or both depending on options passed to your script.

[lomcevak]

I like colucix's solution as well. Problem is I don't fully understand how the exec command works. I did figure out how to turn it off in the script if you wish as follows:

logfile=$$.log
exec 3>&1
exec > $logfile 2>&1
echo Hi1
exec 1>&3 3>&-
echo Hi2