Jan Kończak

3	pwd; ls
4	cd Desktop && ls
5	ping put.poznan.pl Ctrl+Z jobs fg Ctrl+C
6	ping put.poznan.pl & # that command will spam the screen with its results, but the shell still normally accepts commands jobs fg Ctrl+Z bg
7	echo $VAR VAR=text echo $VAR
8	OTHER=$VAR echo $OTHER
9	SIZE=5 echo "The file size is ${SIZE}MB"
11	#!/bin/sh echo "First arg: $1" echo "Third arg: $3"
12	#!/bin/sh echo "This script has been called as $0 and has $# arguments."
13	LANG=ja_JP.UTF-8 date vim     :q LANG=de_DE.UTF-8 rm -rf /root/.ssh/nope lscpu
14	PS1="\w> " PS1="\[\e[1;30m\][\[\e[33m\]\u\[\e[30m\]@\[\e[34m\]\h\[\e[0;1m\] \w\[\e[30m\]]\$\[\e[0m\] " # (There are plenty prompt generators in the Internet)
15	lspci PATH="/sbin:/usr/sbin:$PATH" lspci
16	X=42 Y=42 X=$((X+1)) Y=$((Y+2)) Z=$((X*Y)) echo $((Z%128))
	# You may also abuse the syntax and run:   echo $((X=43, Y=42, X=X+1, Y=Y+2, Z=X*Y, Z%128))
17	echo "In the current directory there are $(ls | wc -l) files"
18	pstree -au > processes_$(date +%H_%M_%S).log
19	START=$(date +%s%N); sleep 1; END=$(date +%s%N); echo $((END-START))
20	alias year="cal -my" year 2025

Exercise 21

#!/bin/sh
echo "What is your name:"
read NAME
echo "Hello $NAME!"

Exercise 22

#!/bin/sh
read ONE TWO
echo $((ONE+TWO))

Exercise 23

[ -d dirname ] && cd dirname

X=1 Y=2
[ "$X" -gt "$Y" ] || echo "Y≥X"

Exercise 24

if rm filename
then
  echo "Removed the file"
else
  echo "Failed to remove the file" 
fi

Exercise 25

#!/bin/sh
if [ $# -ne 2 ]
then
    echo "Wrong number of arguments"
    exit 1
fi
 
if [ "$1" -le "$2" ]
then
    :
else
    # notice that 'else' branch is executed also for non-number arguments; [ "$1" -gt "$2" ] would fail for non-numeric arguments
    echo "the first argument must be lesser then or equal to the second argument"
    exit 1
fi

Exercise 26

#!/bin/sh
case "$1" in
    *.pdf) pdftotext "$1" -;;
    *.zip) unzip -l "$1";;
    *)   cat "$1";;
esac

Exercise 27

#!/bin/sh
for VAR in "$@" # 'in "$@"' can be left out, as "$@" is the default argument list for the for loop
do
    echo "=== $VAR ==="
    head -n1 "$VAR"
    tail -n1 "$VAR"
done

Exercise 28

#!/bin/sh
for POW in $(seq ${1:-20})
do
  echo "2**$POW=$((2**POW))"
done

Exercise 29

#!/bin/sh
E=1
V=2
while ((V<${1:-10000}))
do
  echo "2**$E=$V"
  V=$((V*2))
  E=$((E+1))
done

Exercise 30

#!/bin/sh
NUM=0
while [ -e myProg_$NUM.log ]
do
  NUM=$((NUM+1))
done
LOG=myProg_$NUM.log
date > $LOG

Exercise 31

user@host ~ $ myFunction(){ echo "Hello world!"; }
user@host ~ $ myFunction
Hello world!

Exercise 32

user@host ~ $ repeatText(){ for I in $(seq $1); do echo "$2"; done; }
user@host ~ $ repeatText 3 "Example text."
Example text.
Example text.
Example text.

Exercise 33

myTree(){
  ls -A "$1" 2>/dev/null | while read F
    do
      echo "$2$F"
      [ ! -L "$1/$F" -a -d "$1/$F" ] && myTree "$1/$F" "  $2"
    done
}

Exercise 34

user@host ~ $ trap "fortune" INT
user@host ~ $ ^C
Falling rock.
user@host ~ $

Exercise 35

#!/bin/sh
TEMPFILE=$(mktemp)
trap "echo \"Cleaning up the temporary file $TEMPFILE\"; rm $TEMPFILE" exit
echo "Created a temporary file $TEMPFILE"
date > "$TEMPFILE"
sleep 12s
date >> "$TEMPFILE"