Conditional variables in bash script? - bash

Question

I'm not used to writing code in bash but I'm self teaching myself. I'm trying to create a script that will query info from the process list. I've done that but I want to take it further and make it so:
The script runs with one set of commands if A OS is present.
The script runs with a different set of commands if B OS is present.
Here's what I have so far. It works on my Centos distro but won't work on my Ubuntu. Any help is greatly appreciated.
#!/bin/bash
pid=$(ps -eo pmem,pid | sort -nr -k 1 | cut -d " " -f 2 | head -1)
howmany=$(lsof -l -n -p $pid | wc -l)
nameofprocess=$(ps -eo pmem,fname | sort -nr -k 1 | cut -d " " -f 2 | head -1)
percent=$(ps -eo pmem,pid,fname | sort -k 1 -nr | head -1 | cut -d " " -f 1)
lsof -l -n -p $pid > ~/`date "+%Y-%m-%d-%H%M"`.process.log 2>&1
echo " "
echo "$nameofprocess has $howmany files open, and is using $percent"%" of memory."
echo "-----------------------------------"
echo "A log has been created in your home directory"
echo "-----------------------------------"
echo " "
echo ""$USER", do you want to terminate? (y/n)"
read yn
case $yn in
[yY] | [yY][Ee][Ss] )
kill -15 $pid
;;
[nN] | [n|N][O|o] )
echo "Not killing. Powering down."
echo "......."
sleep 2
;;
*) echo "Does not compute"
;;
esac

Answer 1

Here's my version of your script. It works with Ubuntu and Debian. It's probably safer than yours in some regards (I clearly had a bug in yours when a process takes more than 10% of memory, due to your awkward cut). Moreover, your ps are not "atomic", so things can change between different calls of ps.
#!/bin/bash
read percent pid nameofprocess < <(ps -eo pmem,pid,fname --sort=-pmem h)
mapfile -t openfiles < <(lsof -l -n -p $pid)
howmany=${#openfiles[#]}
printf '%s\n' "${openfiles[#]}" > ~/$(date "+%Y-%m-%d-%H%M.process.log")
cat <<EOF
$nameofprocess has $howmany files open, and is using $percent% of memory.
-----------------------------------
A log has been created in your home directory
-----------------------------------
EOF
read -p "$USER, do you want to terminate? (y/n) "
case $REPLY in
[yY] | [yY][Ee][Ss] )
kill -15 $pid
;;
[nN] | [n|N][O|o] )
echo "Not killing. Powering down."
echo "......."
sleep 2
;;
*) echo "Does not compute"
;;
esac
First, check that your version of ps has the --sort flag and the h option:
--sort=-pmem tells ps to sort wrt decreasing pmem
h tells ps to not show any header
All this is given to the read bash builtin, which reads space-separated fields, here the fields pmem, pid, fname and puts these values in the corresponding variables percent, pid and nameofprocess.
The mapfile command reads standard input (here the output of the lsof command) and puts each line in an array field. The size of this array is computed by the line howmany=${#openfiles[#]}. The output of lsof, as stored in the array openfiles is output to the corresponing file.
Then, instead of the many echos, we use a cat <<EOF, and then the read is use with the -p (prompt) option.
I don't know if this really answers your question, but at least, you have a well-written bash script, with less multiple useless command calls (until your case statement, you called 16 processes, I only called 4). Moreover, after the first ps call, things can change in your script (even though it's very unlikely to happen), not in mine.
You might also like the following which doesn't put the output of lsof in an array, but uses an extra wc command:
#!/bin/bash
read percent pid nameofprocess < <(ps -eo pmem,pid,fname --sort=-pmem h)
logfilename="~/$(date "+%Y-%m-%d-%H%M.process.log")
lsof -l -n -p $pid > "$logfilename"
howmany=$(wc -l < "$logfilename")
cat <<EOF
$nameofprocess has $howmany files open, and is using $percent% of memory.
-----------------------------------
A log has been created in your home directory ($logfilename)
-----------------------------------
EOF
read -p "$USER, do you want to terminate? (y/n) "
case $REPLY in
[yY] | [yY][Ee][Ss] )
kill -15 $pid
;;
[nN] | [n|N][O|o] )
echo "Not killing. Powering down."
echo "......."
sleep 2
;;
*) echo "Does not compute"
;;
esac

Answer 2

You could achieve this for example by (update)
#!/bin/bash
# place distribution independent code here
# dist=$(lsb_release -is)
if [[ -f /etc/redheat-release ]];
then # this is a RedHead based distribution like centos, fedora, ...
dist="redhead"
elif [[ -f /etc/issue.net ]];
then
# dist=$(cat /etc/issue.net | cut -d' ' -f1) # debian, ubuntu, ...
dist="ubuntu"
else
dist="unknown"
fi
if [[ $dist == "ubuntu" ]];
then
# use your ubuntu command set
elif [[ $dist == "redhead" ]];
then
# use your centos command set
else
# do some magic here
fi
# place distribution independent code here