Shell script code not really understandable for me

digioleg54 · April 5, 2017, 9:16am

I have a script:

 DAYS=10
 print_usage() {
        echo "\n"
        echo "Usage: $PROG [-days] [-file|-dir] dir1 [ dir2 ... dirN]"
        echo "       This program will delete all file/directories that are beyond "
        echo "       'x days' old."
        echo "           -days      - This flag allows you to define x days [default:10]"
        echo "           -file|-dir - This flag allows one to remove files [default: directories]"
        echo "\n"
}
  
  
         while [ ! -z "$1" ]
        do
                case $1 in
                        -file* | -f*)
                                TYPE="f"
                                ;;
                        -link* | -l*)
                                TYPE="l"
                                ;;
                        -dir* | -d*)
                                TYPE="d"
                                ;;
                        -1* | -2* | -3* | -4* | -5* | -6* | -7* | -8* | -9* | -0* )
                                DAYS=`echo $1 | awk -F- '{printf("%d",$2)}'`
                                ;;
                        -* )
                                print_usage
                                exit -3
                                ;;
                        * )
                                if [ -d $1 ]
                                then
                                        if [ "$TYPE" = "f" or "$TYPE" = "l" ]
                                        then
                                                echo "Searching $1 for files that are $DAYS days old"
                                                find $1 -type $TYPE -mtime +$DAYS -print -exec /usr/bin/rm -f {} \;
                                        else
                                                echo "Searching $1 for directories that are $DAYS days old"
                                                TMP_LOG=$LOG_HOME/delete.$$
                                                find $1/* -type $TYPE -mtime +$DAYS -print > ${TMP_LOG}
                                                cat $TMP_LOG
exit;
                                                for rm_file in `cat $TMP_LOG | grep -v 'log$'`
                                                do
                                                        if [ -d ${rm_file} ]
                                                        then
                                                                /usr/bin/rm -rf ${rm_file}
                                                        else
                                                                echo "Skipping ${rm_file} because, either root dir is removed or it is not a directories"
                                                        fi
                                                done
                                                /usr/bin/rm -f $TMP_LOG
                                        fi
                                 else
                                        echo "Following is NOT a DIRECTORY: $1"
                                fi
                 esac

We call this script from another like this:

 /export/applications/dte/sh/clean_disk.sh -60        /export/applications/dte/web/release 
  
 /export/applications/dte/sh/clean_disk.sh -14 -file  ${DTE_WDATA_DIR}/log
  
  /export/applications/dte/sh/clean_disk.sh -30 -link  /export/applications/dte/web/data/outfiles

I don't understand, why case we check $1 and try to set up type as file, link, dir, if $1 is always DAYS
And why script is checking $1 as directory, when we definitely know that it is a number?

Thanks for contribution

durden_tyler · April 5, 2017, 11:22am

digioleg54:

...
...
 DAYS=10
 print_usage() {
   echo "\n"
   echo "Usage: $PROG [-days] [-file|-dir] dir1 [ dir2 ... dirN]"
   echo "       This program will delete all file/directories that are beyond "
   echo "       'x days' old."
   echo "           -days      - This flag allows you to define x days [default:10]"
   echo "           -file|-dir - This flag allows one to remove files [default: directories]"
   echo "\n"
}
  
  
...
 ...
 
...
I don't understand, why case we check
$1
and try to set up type as file, link, dir, if
$1 
is always DAYS
And why script is checking CODE]$1 [/CODE] as directory, when we definitely know that it is a number?
...

I think it is a generally accepted convention that square brackets ("") means the argument is optional.
So, in your script, only "dir1" is mandatory - the rest of the arguments are optional.
In other words, $1 will be a number if it is specified.

You could, alternatively, execute your script as such:

 /export/applications/dte/sh/clean_disk.sh /export/applications/dte/web/release

For such an invocation, dir1 is "/export/applications/dte/web/release"
and DAYS takes the default value of 10.
Which is the same as:

 /export/applications/dte/sh/clean_disk.sh -10 /export/applications/dte/web/release

(At least that is what the "print_usage" function tries to convey. I haven't really reviewed or tested your script to see if it actually does what it says it does.)

Corona688 · April 5, 2017, 11:32am

I think you left out an important part of the script. There must be a "shift" somewhere below that "esac", which will change the value of $1.

When $1="A", $2="B", $3="C", shift tosses the value of $1 then sets $1="B", $2="C".

If you give shift a value, like shift 2, it deletes n leading arguments, not just one.

In this manner you can loop through all arguments while just checking $1.

I don't like the way they do the loop, though. Just because an argument is blank doesn't mean its the last argument, what if it's supposed to be blank for some reason?

digioleg54 · April 5, 2017, 11:53am

Sorry, you are right. There is a shift and I already understand, what is going on

Thanks for contribution