[SOLVED] [bin/sh] How to loop over a variable

MrKementari · 06-15-2018, 07:26 AM

Hi everybody,

I'm stuck on a simple issue but I can't fix it...
On purpose to monitor filesystems space, I use the following command to get all filesystems :

Code:

myvar=$(df -Pk | egrep "[myFS]")

For example, with /run, I get the following :

Code:

tmpfs               202860    8836    194024       5% /run
tmpfs                 5120       0      5120       0% /run/lock
cgmfs                  100       0       100       0% /run/cgmanager/fs
tmpfs               202860      44    202816       1% /run/user/1000

I would like to get size and name values of each line, so I need to loop through the "myvar" variable, but it's not working...

I tried to do some stuff like :

Code:

while IFS='' read -r line; do
...
done <<< "$myvar"

It works with bin/bash but not with bin/sh... and I have to use bin/sh because target servers don't have bash installed.

Somebody has a solution ?

Thanks a lot.

Edit : Except if it's really needed, I don't want to use temporary files either.

pan64 · 06-15-2018, 07:59 AM

Hm. Probably I would try yo use awk/gawk/perl/python/whatever

Guttorm · 06-15-2018, 08:07 AM

Here's a little script I've used for years on one server. It checks disk usage on some servers every night.

Code:

for server in $(cat serverlist.txt) ; do
    ssh $server "df -Hl" | grep -vE '^Filesystem|tmpfs|cdrom' | awk '{ print $5 " " $1 }'  | while read output ; do
        usep=$(echo $output | awk '{ print $1}' | cut -d'%' -f1  )
        [ -z "$usep" ] && continue
        partition=$(echo $output | awk '{ print $2 }' )
        if [ "$usep" -ge 90 ]; then
                echo "Running out of space "$partition ($usep%)" on $server as on $(date)"
        fi
    done
done

I can't remember why tmpfs is skipped. It could probably be more elegant and faster. But it works on many different/old/new servers, and some using dash and some using bash.

It outputs the server and partion, so when it's run by cron, I get a mail when some disk is over 90% full. You could probably modify it for your needs.

NevemTeve · 06-15-2018, 08:23 AM

@OP: Then don't use bash-specific features. Try this:

Code:

df -Pk | egrep "[myFS]" | while read Filesystem Total Used Available Capacity MountedOn; do
 ...
done

MrKementari · 06-15-2018, 08:33 AM

Thanks for all your answers.

I found a way by myself, doing this :

Code:

IFS='
'
for ligne in $var; do
...
done

I set the topic as solved, thanks everybody !

MadeInGermany · 06-18-2018, 12:29 AM

The for list is subject to word splitting (on IFS) and wildcard expansion. You should also disable the latter with

Code:

set -f

The while-read loop, as given in the previous post, is more robust because it reads lines. It can read the line into one variable, or, as demonstrated, it can split the line (on IFS) into variables, that is often useful for further processing. The only disadvantage of piping to while-read is that the while-do-done block runs in a sub shell; defined variables are lost after the block.