Bash

Question 1

retrieve the value of the variable x

Answer 1

$x

Question 2

explicitly declare variable to integer or array

Answer 2

declare -i i

declare -a A

Question 3

print string including variable x

Answer 3

echo “Hei, $x”

Question 4

command line arguments

Answer 4

$#
$1, $2, $3…
$@ for all

Question 5

exit status of the last executed command

Answer 5

$?

Question 6

comparisons and if-statements

Answer 6

Integer comparison (but don’t use it)
if [ $i -eq 10 ]; then
…
fi

String comparison
if[ “$name” == “Henrik” ]; then
…
fi

Solution: Assume all variables are strings and use double quotes when comparing

Question 7

verbose

Answer 7

!/bin/sh -x

Question 8

list files in tree

Answer 8

ls -R # –Recursive

Question 9

search

Answer 9

fgrep [pattern] [file] -r # fixed
grep [pattern] [file] -r # regex

ls | grep ^A

Question 10

store result of command as a variable

Answer 10

time = $(date)

Question 11

list files sorted

Answer 11

ls -s | sort -r

ls -Ss

Question 12

if/else-statements

Answer 12

if [ -a $path ]; then
    ...
elif [ -d $path ]; then
    ...
else
    ...
fi

Question 13

write to file from stdin

Answer 13

cat > file.txt

Question 14

while-loop

read command arguments one by one

Answer 14

while [ $# -gt 0 ]
do
    print $1;
    shift;
done

Question 15

append to file

Answer 15

cat appendThis&raquo_space; toThis

Question 16

for-loop removing all PDF-files

Answer 16

files = ‘ls *.pdf’

for file in $files
do
rm -f $file
done

Question 17

arithmetic expressions

Answer 17

((counter++))

declare -i i
for ((i=0; i < $n; i++)); do
…
done

Question 18

search for files and run a command for each file

Answer 18

find dir -name *.txt -exec cat {} \;
# {} is the current filename

Question 19

man find

Answer 19

• name ‘*.pdf’
• type f
• size +200
• exec … {} \;
• atime +90 # days
• print

Question 20

pack files into one file

Answer 20

tar -cvf files.tar mytree file1 file2

Question 21

unpack tar

Answer 21

tar -xvf files.tar

Question 22

list new files

Answer 22

declare -i minuteLimit = “$2*3600”

find $1 -type f -mmin -$minuteLimit -print | xargs ls -1Ssk

Question 23

remove large files

Answer 23

find $1 -type f -size +$2k -print -exec rm {} \;

Question 24

sort file into another file

Answer 24

sort $1 -o $2