how to use a nested if and perform correct file checks in unix

Question

Need some shell scripting help, especially with my if-then-else logic. I want to combine both conditions, but not sure if the file checks will work the same? Should I be doing something like a nested if?? My script uses the if statements to do file checks to see if they exist, then do something..

There is probably a better way to do file checks part too.

Any help, critique would be appreciated. Thanks.

Here's my code, it sort of works.

if [ $# != 1 ]; then
    echo "Usage: getlogs.sh <remote-host>" 2>&1
    exit 1
fi

#Declare variables
STAMP=`date '+%Y%m%d-%H:%M'`
REMOTE_MYCNF=/var/log/mysoft/mysoft.log
REMOTE_GZ=/var/log/mysoft/mysoft.log.1.gz
REMOTE_DIR=/var/log/mysoft/
BACKUP_DIR=/home/mysql/dev/logs/
NEWLOG="foo-temp.log"
export REMOTE_MYCNF STAMP SHORTNAME
export REMOTE_DIR REMOTE_GZ

#Copy file over
echo "START..." 2>&1
test -f $BACKUP_DIR$1.mysoft.log
if [ $? = 0 ]; then
   echo "Local log file exists, clean up for new copy..." 2>&1
   /bin/rm $BACKUP_DIR$1.mysoft.log
   exit 0
   else
        echo "File does not exist, getting a new copy..." 2>&1
fi

echo "Checking remotely in $1 for foo logfile $REMOTE_MYCNF $STAMP" 2>&1
if [ ! -f $REMOTE_MYCNF ]; then
   echo "File exists remotely, creating new logfile and copy here...." 2>&1
   ssh $1 "zcat $REMOTE_GZ >> $REMOTE_DIR$NEWLOG"
   ssh $1 "cat $REMOTE_MYCNF >> $REMOTE_DIR$NEWLOG"
   /usr/bin/scp $1:$REMOTE_DIR$NEWLOG $BACKUP_DIR$1.mysoft.log
   echo "end remote copy" 2>&1
   echo "Cleaning up remote files" 2>&1
   ssh $1 "rm $REMOTE_DIR$NEWLOG"
   exit 0
   else
        echo "Unable to get file" 2>&1
        exit 0
fi

Updated code using help:

    if [ -f $BACKUP_DIR$1.mysoft.log ]; then
       echo "Local log file exists, clean up for new copy..." 2>&1
       /bin/rm $BACKUP_DIR$1.mysoft.log
       exit 0
    else
        echo "File does not exist, getting a new copy..." 2>&1
        echo "Checking remotely in $1 for foo logfile $REMOTE_MYCNF $STAMP" 2>&1
               if [ ! -f $REMOTE_MYCNF ]; then
                    echo "File exists remotely, creating new logfile and bring a copy here...." 2>&1
                    ssh $1 "zcat $REMOTE_GZ >> $REMOTE_DIR$NEWLOG"
                    ssh $1 "cat $REMOTE_MYCNF >> $REMOTE_DIR$NEWLOG"
                    /usr/bin/scp $1:$REMOTE_DIR$NEWLOG $BACKUP_DIR$1.mysoft.log
                    echo "end remote copy" 2>&1
                    echo "Cleaning up remote files" 2>&1
                    ssh $1 "rm $REMOTE_DIR$NEWLOG"
                    exit 0
               else
                    echo "Unable to get file" 2>&1
                    exit 0


         fi
fi

Answer 1

The file test can be combined into one statement like this:

if [ -f $BACKUP_DIR$1.mysoft.log ]; then

At a glance, it doesn't look like you need to export any of the variables.

If you intend for the if [ ! -f $REMOTE_MYCNF ]; then block to be executed within the else of the previous if, just move it within it.

if ...
then
   foo
else
    if ...
    then
        bar
    else
        baz
    fi
fi

If you need to check two things:

if [ "$foo" = "bar" && "$baz" = "qux" ]

Always quote your variables.

In a short script it's fine to use positional parameters such as $1 directly, but it makes a longer script easier to understand if a variables with meaningful names are assigned their values near the top.

remote_host=$1

When you want to echo errors to stderr do it this way:

echo "Message" >&2

The way you have it, you're echoing the message and any errors the echo itself may produce (pretty rare) to stdout.