Target:
Another howto for beginners. This time I focused on helpful commands for scripts.
Premise
The first time I used linux shell, i could not do the simplest operations.
A program that has helped me to survive is Midnight Commander (mc).
The appearance reminds Total Commander (in fact comes from the venerable Norton Commander for DOS).
Installation is simple:
yum install mc
To run, simply type
mc
To use it, scroll to the desired file (space bar for multiselection) and run the operations required by pressing the keys F1 through F10 (F10 exits the program).
It 'very interesting the file editing function (F3 to read, F4 to change).
To edit files you do not need to go through the mc interface. you can start the editor (similar to the edit DOS) with command mcedit
mcedit /etc/aliases
Customizing the shell
The shell allows different customizations to fit our needs.
alias allows you to create keyboard shortcuts
alias lsdir='ls -la |grep '^d''
If I type lsdir performs the dir of folders
ctrlaltdel sets the function of the combination CTRL+ALT+DEL
ctrlaltdel soft
kbdrate Sets the keyboard repeat rate and its delay time
kbdrate -r 30 -d 250
loadkeys load a keyboard layout
loadkeys it
Set environment variables
pathown="/var/www/html/owncloud"
ls $pathown
If you enter into a script you must make available at the end of the script with command export
The variables will be called up with the $ symbol.
To always have available these settings you can enter the user’s login script ~/.bash_profile or ~/bashrc
Example:
[root@nethservice ~]# more .bash_profile
# .bash_profile
# Get the aliases and functions
if [ -f ~/.bashrc ]; then
. ~/.bashrc
fi
# User specific environment and startup programs
PATH=$PATH:$HOME/bin
export PATH
alias lsdir='ls -la|grep '^d''
pathown=/var/www/html/owncloud
export pathown
Shell Script
Reading information:
When you create a shell script, especially if unattended, it is often necessary to retrieve information of the machine or of his state.
There are some commands to the aid:
hostname: displays and changes the hostname.
groups: Print the name of a user group.
groups root
dirname: Printing only the directory of a file.
dirname /etc/samba/smb.conf
return /etc/samba
pwd: It returns the path of the current location. It can be assigned to a variable.
mypath=`pwd`
(Reverse quotes: pressing alt, type 096)
arch: information about the system architecture.
arch
In my case returns “x86_64”
date: returns the date and time. good to create log file with unique name and so on.
date
Tue Jul 12 15:20:47 CEST 2016
date +%Y%m%d-%H%M%S
20160712-151649
last: return the list of last login
logname: return the login name
users: return the list of logged users
###Returning information:
Output to system logs
logger: write on /var/log/messages.
logger -t MYSCRIPT "Run script"
Output to video
echo "Run script"
clear: clean video
Output to file
echo "Run script" > myfile.log
more myfile.log
column: displays files in columns according to a separator (-s)
find /var/log/ > /tmp/list.txt
column -s"/" -t /tmp/list.txt
Output to mail
mail: simple mail program
echo "Mail text" |mail -s "Mail Object" -a /tmp/list.txt mymail@mydomain.it
###Working on files
Create file
touch: change date and time of a file (if it does not exist, create it).
touch -d 2016-06-01 myfile.txt
other file creation methods:
command > myfile.txt
echo "pippo" > myfile.txt
ls > myfile.txt
###Processing text files
cut: splits into columns the lines of a file according to a separator (-d) and returns required columns (-f)
find /var/log/ > /tmp/list.txt
cut -d "/" -f 4,5 /tmp/list.txt |more
splits the lines according to / and returns columns 4 and 5
find /var/log/ > /tmp/list.txt
cut -c1-3 /tmp/list.txt
Returns, for each line, the characters from 1 to 3
colrm: remove columns from a file.
find /var/log/ > /tmp/list.txt
colrm 1 5 < /tmp/list.txt
basename: Remove directory and suffix from file name.
basename /tmp/myfile.txt
return myfile.txt
basename /tmp/myfile.txt .txt
return myfile
sort: Sort lines of text. alphabetic, numeric (-n) reverse (-r)
sort -n myfile.txt
ls -1 | sort -r
split: split a file based on the lines or bytes.
split -l 20 myfile.txt
creates n files with 20 lines
nl: numbers the lines of a file.
nl myfile.txt
todos: convert files from Unix format to MSDOS
diff: Check differences between two files.
diff fileA fileB
diff3: Check 3 file.
Other commands (sed, awk, grep) are available on:
###Rights files
chgrp: change the group of a file.
chgrp root.locals /tmp/myfile.txt
chmod: Change rights of a file.
chmod 644 /tmp/myfile.txt
chmod +x /tmp/myfile.txt
chown: change owner of a file or directory.
chown root /tmp/myfile.txt
All commands accept the -R switch to perform the change recursively Caution!!.
cd /tmp
chmod 644 * -R
Get file
wget: download files from web and ftp;
wget https://www.google.it/images/branding/googlelogo/2x/googlelogo_color_272x92dp.png
curl: retrieves content from a html page
curl http://community.nethserver.org > /tmp/neth.html
In case of compressed files
gzip : compresses and decompresses .gz file.
Max compression (-9) on a new file (-c):
gzip -9 myfile.txt -c > myfile.txt.gz
To unzip a file
gzip -d myfile.txt.gz
bzip2 : compresses and decompresses .bz2 file
Compression
bzip2 -zkv filename
Unzip
bzip2 -x filename.bz2
zdiff: Like diff for compressed files.
zgrep: Like grep for compressed files.
zcat: Like cat for compressed files.
Loop operations
for:
Syntax
for [ condition ]
do
command1
....
commandX
done
Example
for i in 1 2 3
do
echo $i
done
or in one line
for i in 1 2 3; do echo $i; done
while
syntax
while [ condition ]
do
command1
....
commandX
done
Example
x=1
while [ $x -le 5 ]
do
echo "Value x = $x"
x=$(( $x + 1 ))
done
or in one line
x=1; while [ $x -le 5 ]; do echo "Value x = $x"; x=$(( $x + 1 )); done
sleep: freezes for x Seconds (s) Minutes (m) Hours (h) Days (d).
sleep 5s
Planning script
crontab: starts a process at a certain time.
List of cron jobs
crontab -l
Create a new job
crontab -e
the syntax will be as the following
00 00 * * * /Script/myscript.sh
where the fields are
minute hour day_of_the_month month day_of_the_week Script_to_execute
Script Example
This Script remove mail from trash for all users.
For safety, the command that deletes emails is commented
# variable
mail_path="/var/lib/nethserver/vmail/"
mytime=`date +%Y%m%d-%H%M%S`
recipient="mymail@mydomain.com"
echo -e "\nStart cleaning Script on $myserver by user $myuser\n" > Log-$mytime
logger -t SCRIPT_CLEAN "Start cleaning Script"
for i in `ls -1 $mail_path` ; do
# write log event
logger -t SCRIPT_CLEAN "Clean Trash $i"
# write log file
echo -e "Clean trash for user $i in the path $mail_path$i/Maildir/.Trash/cur" >> Log-$mytime
# write on video
echo -e "Clean trash for user $i in the path $mail_path$i/Maildir/.Trash/cur..."
echo -e "...OK"
# Cleaning command (uncomment at your risk)
# rm -Rf $mail_path$i/Maildir/.Trash/cur/*
done ;
# Send log
echo "Cleaning work completed" |mail -s "Script clean trash $mytime" -a Log-$mytime $recipient
To run the script every Friday at 20, the cron entry (crontab -e )should be:
00 20 * * 5 /script/myscript.sh
I refer
