Bash script help
 

Hello, all.

I'm creating a bash script to check how much free space is left in /var directory then, if it hits a certain threshold, delete certain files with numbers for extensions (e.g. fileA.1, fileA.2 fileA.3, and fileA.4, fileB.1, fileB.2 fileB.3, and fileB.4 ). Here's a snippet from my script:

if [ $PARTUSE -ge $ALERT ]; then
cat /dev/null > /var/log/fileA.* 2>&1 &&
cat /dev/null > /var/log/fileB.* 2>&1 &&
cat /dev/null > /var/log/fileC.* 2>&1 &&
echo "Reclaimed disk space on \"$PARTITION\" now ($PARTUSE% full) on $(hostname) as of $(date)" |
mail -s "Reclaimed disk space - $PARTITION on $(hostname)" $ADMIN
fi

If I use a * as a wildcard for the number extension, the script fails. Maybe regex would work here, but I'm not particularly accomplished at it. Or some other construct.

Your help would be most appreciated.

Diggy

You cannot redirect the standard output to multiple files at once. You can use a loop to empty every single file, e.g.
Note you don't need cat /dev/null. In bash/ksh the redirection symbol alone creates/overwrite a file as if the null command was executed. Hope this helps.

The colucix is the right approach...

Nope. To me it creates a literal fileA.* since escaping prevents expansion.

colucix,

I used a poor example (apologies) in decribing what I want to do. I really want to delete files along the lines of Afile.1, Afile.2, Bfile.1, Bfile.2. Given that, How would I write the construct you suggested if, in fact, it would still work in this case?

Diggy

And why you don't just use a rm command for that?
Too risky?
May it's not so clear (to me!) the phrase

sorry!

I don't want to destroy the files, just empty them of content.

Diggy

As colucix suggested should only empty the files, not delete them.

This actually empties the content of the file:
What are your doubts about the suggested loop?

colucix,

I'm sure that your solution 1) works, and 2) is "elegant". I (ashamedly) just don't have a lot of scripting experience. That said, would my entire script look like this?:

#!/bin/bash
#
# Shell script to reclaim disk space
# It will clear out certain files if the percentage of partition space used is >= % set in ALERT variable,
# thus reducing partition size, and will send an email to the system administrator(s)
# -------------------------------------------------------------------------
# Written by Me
# -------------------------------------------------------------------------
#
# set admin email address(es)
ADMIN="root@localhost"
#
# set alert level at 90%. If used space exceeds this, send alert
ALERT=80
#
# check partition space and, if necessary, send alert
df -H | grep '/var' | awk '{ print $5 " " $6 }' | while read output;
do
PARTUSE=$(echo $output | awk '{ print $1}' | cut -d'%' -f1 )
PARTITION=$(echo $output | awk '{ print $2 }' )
if [ $PARTUSE -ge $ALERT ]; then
for file in /var/log/Afile.? /var/log/Bfile.? /var/log/Bfile.?
do
> $file
done &&
echo "Reclaimed disk space on \"$PARTITION\" now ($PARTUSE% full) on $(hostname) as of $(date)" |
mail -s "Reclaimed disk space - $PARTITION on $(hostname)" $ADMIN
fi
done


Please bear with me, I'm learning, and this will be invaluable.

Diggy

Hey, no problem at all! I was just trying to clarify! :)

Regarding your script it looks good. I would avoid some redundancy, anyway. For example, to extract the usage of the /var partition you might use a more compact code. In place of:
you can simply do:
Notes:

1. the -H option of df is not really necessary, since you're not intersted in the actual sizes but only in the percentage. Instead the -P option is useful, since it causes the df output to be in a more standard format. There are situations where the device name is very long and a line of output can be splitted in two parts. The -P option prevents this behaviour.
2. awk is a very powerful language that manages regular expressions, so that the grep command is not necessary. Moreover it can remove the % sign, so that you can avoid the cut command.
3. the read statement accept multiple variable names. The input will be splitted to fill all the specified variables, so that you can assign PARTUSE and PARTITION simultaneously.

Finally I don't see the need for a while loop, since you're reading a single line. To assign the output of a command using the read statement, process substitution is your friend:
Hope this helps! :)

What you suggest looks just fine, but I'm not sure how the final product would look. Based on my knowledge, and the suggestions in your last post, I'm not seeing where/how the files are being concatenated.

I understand that this piece:

df -P | awk '/\/var/{ sub(/%/,"",$5); print $5, $6 }' | while read PARTUSE PARTITION
do

replaces:

df -H | grep '/var' | awk '{ print $5 " " $6 }' | while read output
do
PARTUSE=$(echo $output | awk '{ print $1}' | cut -d'%' -f1 )
PARTITION=$(echo $output | awk '{ print $2 }' )

After the "do" statement, do I place my email alert piece? What handles the actual file concatenation?

I'm a bit confused, and feeling not just a little stupid.

Diggy

It simply replaces the extraction of information from the df output and it does the assigment to PARTUSE and PARTITION in a different way, but the rest stays untouched:

I apologize, again. I didn't mean to have you write this for me. But, now I get it. I'll test in a while, and report back. Thanks for your patience!!

Diggy

You're welcome! :)