commands and switches

Question 1

find [path] -name “[name]”

Answer 1

find files and subdirs

Question 2

find [path] -type d -name “[dir]”

Answer 2

find subdirs

Question 3

ldconfig –print-cache

Answer 3

Print the lists of directories and candidate libraries stored in the current cache. Pipe into grep to find if a particular library is installed and accessible.

Question 4

type [cmd]

Answer 4

Find whether the given command is an alias, shell built-in, file, function, or keyword. Also displays path

Question 5

type -t [cmd]

Answer 5

Show just type

Question 6

type -p [cmd]

Answer 6

Show just path

Question 7

type -a [cmd]

Answer 7

Show all info

Question 8

du [paths]

Answer 8

Disk usage

Question 9

du -h [path]

Answer 9

Disk usage in human readable form

Question 10

strace -f [program]

Answer 10

Trace child processes

Question 11

strace -o “filename”

Answer 11

Output to log

Question 12

strace -p PID

Answer 12

Attach

Question 13

strace trace=open

Answer 13

Show opened files

Question 14

rename ‘s/[old regex]/[new regex]/’

Answer 14

Batch rename

Question 15

rename ‘s/-//’ ./*

Answer 15

remove dashes in all names in current folder: (1st dash)

Question 16

grep [path] -e [pattern]

Answer 16

Search for pattern in path

Question 17

grep -r

Answer 17

recursive

Question 18

grep -n

Answer 18

display line number

Question 19

grep -w

Answer 19

search for whole word

Question 20

grep -l

Answer 20

show just file names

Question 21

[[ -a file ]]

Answer 21

Test if file/dir exists. Identical to -e

Question 22

[[ -d file ]]

Answer 22

Test if directory exists

Question 23

[[ -f file ]]

Answer 23

True if file exists and is a regular file.

Question 24

[[ -e file ]]

Answer 24

Test if file/dir exists. Identical to -a

Question 25

[[ -r file ]]

Answer 25

True if file exists and is readable

Question 26

[[ -s file ]]

Answer 26

True if file exists and has a size greater than zero.

Question 27

[[ -w file ]]

Answer 27

True if file exists and is writable

Question 28

[[ -x file ]]

Answer 28

True if file exists and is executable

Question 29

[[ file1 -nt file2

]]

Answer 29

True if file1 is newer than file 2

Question 30

[[ file1 -ot file2 ]]

Answer 30

True if file1 is older than file2

Question 31

[[ -v varname ]]

Answer 31

True if the shell variable varname is set (has been assigned a value).

Question 32

[[ -z string ]]

Answer 32

True if the length of string is zero

Question 33

[[ -n string ]]

Answer 33

True if the length of string is non-zero

Question 34

[[ arg1 -eq arg2 ]]

Answer 34

Arithmetic are equal

Question 35

[[ arg1 -ne arg2 ]]

Answer 35

Arithmetic not equal

Question 36

[[ arg1 -lt arg2 ]]

Answer 36

Arithmetic less than

Question 37

[[ arg1 -le arg2 ]]

Answer 37

Arithmetic less or equal

Question 38

[[ arg1 -gt arg2 ]]

Answer 38

Arithmetic greater than

Question 39

[[ arg1 -ge arg2 ]]

Answer 39

Arithmetic greater or equal

Question 40

[[ arg1 == arg2 ]]

Answer 40

String equality

Question 41

[[ arg1 != arg2 ]]

Answer 41

Strings different

Question 42

[[ arg1 < arg2 ]]

Answer 42

String 1 is lexicographically before string 2

Question 43

ls -l

Answer 43

long listing format

Question 44

ls -A

Answer 44

Almost all files: with hidden, no ./..

Question 45

ls -a

Answer 45

all files: hidden, ./..

Question 46

tail -F some.log

Answer 46

Track while adding

Question 47

rm -f

Answer 47

remove file force: no confirmation

Question 48

file [full path]

Answer 48

auto detect file type

Question 49

ldd [full path]

Answer 49

show static .so dependencies

Question 50

wc

Answer 50

word count

Question 51

wc -l

Answer 51

word count, just lines

Question 52

lsof

Answer 52

list open files

Question 53

lsof +D [path]

Answer 53

list open files within directory

Question 54

lsof +r 5

Answer 54

list open files, refresh every 5 sec

Question 55

ps

Answer 55

active processes by my user

Question 56

ps -u guga

Answer 56

all active processes by user guga

Question 57

uniq -c

Answer 57

Show count of unique entries in sorted input

Question 58

sort [file]

Answer 58

sort lines

Question 59

tcpdump -qns 0 -r [file]

Answer 59

dump pcap contents

• q: quiet, less protocol info
• n: don’t convert ip to names
• s [X]: snap X bytes of data from the packet. -s 0: don’t display the packet
• r: read [file]

Question 60

grep -o

Answer 60

Print only matching parts of a matching line

Question 61

grep -P

Answer 61

Pattern is a perl-compatible regex

Question 62

xargs -n 1

Answer 62

–max-lines=1 : use at most 1 argument per command line

Question 63

xargs -t

Answer 63

synonym to –verbose, show all commands

Question 64

xargs -I % (capital i)

Answer 64

replace % with the input. Doesn’t have to use % as the replace-str

Question 65

xargs -P 7

Answer 65

run at most 7 processes

Question 66

find /tmp -name core -type f -print0 | xargs -0 /bin/rm -f

Answer 66

Find files named core in or below the directory /tmp and delete them, processing filenames in such a way that file or directory names containing spaces or newlines are correctly handled.

Question 67

remote copy (directory)

Answer 67

scp -r username@from_host:/remote/directory/ /local/directory/

Question 68

ls only folders

Answer 68

ls -d */

huh?

Question 69

in htop, show open files

Answer 69

l

Question 70

in htop, strace

Answer 70

s

Question 71

processor bar colors in htop

Answer 71

Blue/green/red: low-pri/normal/kernel threads

Question 72

Memory bar colors in htop

Answer 72

Green/blue/yellow: used/buffer/cache

Question 73

in htop, show env

Answer 73

e

Question 74

xargs show commands

Answer 74

–verbose, -t

Question 75

xargs confirm each command separately

Answer 75

–interactive