Bash Scripting Workshop

Bash Scripting

Prepared by Ahmed Magdy Ezzeldin

File System

● / is not allowed in a file name
● file extensions are not important
● File and folder names are case sensitive
● Names containing spaces are escaped by or ""
● Hidden files start with .
● Current directory alias . and parent directory alias ..
● ls, ls -a, ls -l, cp, mv, rm, rm -rdf, ln, ln -sf

Variable and Strings

● Strings are enclosed in “” '' or just written with spaces escaped
by
VAR=”How are you”
VAR='How are you'
VAR=HOW are you
● Variables
$VAR
${VAR} # e.g. ${FILE}.txt
echo “my name is $NAME”
echo “my name is “$NAME
read VAR
read VAR1 VAR2

Math

● echo $((1+1))
● echo $[1+1]
● echo `expr 1 + 1`
● A=$((B*C))
● let A+=1
● echo "3.4+7/8-(5.94*3.14)" | bc

File Ownership and Permissions

● Group and Ownership
chown, chgrp, ls -l
chown user:group file
sudo chown

● Permissions of files and directories
chmod 755 file
chmod +x file
chmod -x file
(r)ead (w)rite e(x)ecute

4 2 1

Users, su, sudo

● su, sudo, visudo, /etc/sudoers, su user
● sudo bash
● /etc/passwd
● ~/

Processes and Subshells

● ps, pgrep, top, jobs, fg, &, kill, signals
● Sub-shells from :
● Loops
● $()
● Back ticks ``
● bash command
● /proc
● fuser

Loops

● While loop
while read VAR; do echo $VAR; done
● For each loop
for VAR in {1..5}; do echo $VAR; done
for VAR in 1 2 3 4 5; do echo $VAR; done
for VAR in {0..10..2}; do echo $VAR; done
for VAR in $(seq 0 2 10); do echo $VAR; done
● For loop with counter
for (( i=0; i<=10; i+=2 )); do echo $i; done

if and switch case

● If then, else, elif, fi
if [ -d $F ]; then
rm -rdf $F
elif [ -f $F ]; then
rm $F
else
echo “Unknown file type”
fi
● case, esac
while read l; do
case $l in
1) echo "One";;
2) echo "Two";;
3) echo "Three";;
*) echo "Invalid"; break;;
esac
done

I/O Redirection

● >, >>, <, &>, 2&>, 2>, |
echo “error” 1>&2 # redirect std_output to std_err
some_error_producing_command 2>&1
some_command &>> log_file_errors_and_output
some_command >> log_file_output_only
some_command 2>> log_file_errors_only
command | filter_command
command < file
command > file # truncates and writes into file
command1 2>&1 | command2
command1 |& command2
● Mute by redirecting to /dev/null file

Named Pipes and Network and Signal Processing
● Network
exec 9<>/dev/tcp/google.com/80
echo -e "GET / HTTP/1.0nn" >&9
while read line <&9; do echo $line; done
● Named Pipes
mkfifo pipe
while read l; do echo $l; done < pipe
echo “hi” > pipe # on another terminal window
● Signal Processing
#!/bin/bash
function handle_signal () {
echo "Hi man I got the signal"
}
trap "handle_signal; exit" SIGINT
sleep 100

Cool Stuff and GUI
● Install these: libnotify-bin, zenity, festival
● date '+%l oclock' | festival –tts
● zenity --list --hide-header --text="Are you coming today?" --checklist --column
"" --column "" FALSE "Yes" FALSE "No" FALSE "May be"
● zenity --calendar --date-format="%Y/%m/%d"
● zenity --text="Select Hour" --title="Select Hour" --scale --min-value=0 --max-
value=24 --value=17
● zenity --text="Select Minutes" --title="Select Minutes" --scale --min-value=0
--max-value=59 --value=0
● zenity --info --text="Did you know this info"
● zenity --error --text="There is an error"
● zenity --entry | festival --tts
● zenity --file-selection
● <progres command> | zenity --progress --auto-close
● notify-send -t 10 "hi man" "details"

Launchers

● When you drag a file or folder onto a launcher
it is sent as $1 to the launcher script

Example Codes

● Bluetooth Obex-push
NEW_FILE_NAME=`echo $1 | awk -vFS="/" '{print $NF;}'`
ussp-push 00:22:65:89:22:E6@9 "$1" "$NEW_FILE_NAME"
● Close the computer when your browser finishes downloading
your_file
while true; do sleep 5; if [ -z "`fuser ~/your_file`" ]; then break;
fi; done; sudo init 0
● Tell me the time whenever I lock my screen or unlock it
● Simple spider using curl and wget
● Log your time easily and report to a Redmine service
● Think of more ...

References

http://www.linuxcommand.org/lts0040.php

http://www.cyberciti.biz/faq/bash-for-loop/

http://linuxcommand.org/wss0160.php

http://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO-10.html

http://wiki.bash-hackers.org/syntax/redirection

http://www.kernel.org/doc/man-pages/online/pages/man5/proc.5.html

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