Linux Commands Flashcards
Is Linux same as UNIX?
No, they are not the same.
They are different OS and UNIX was created long before Linux, which is said to be UNIX-like OS.
Linux is used pretty much everywhere, PCs, servers, game dev, mobiles etc while unix is mostly used in servers, workstations
What is:
cd ~
Go to home dir of current user
Absolute path vs relative path?
Absolute always starts from root /root/home/kmylonas/Document
If a path starts with / then its an absolute path.
Relative is from where you are now for example if you’re kmylonas:
cd Documets or cd ./Documentrs
rmdir can only remove empty directories?
Yes
How to remove non empty dir?
rm -r
Whats the difference between && and ; ??
&& executes sequence of commands only if all of them succeed
; executes sequence of commands independently, some may fail
What does:
chmod 753 file.txt
file.txt permissions:
user: rwx
group: rx
others: wx
It is equivalent to:
chmod u=rwx,g=rx,o=wx file.xt
Use case of chmod -R ?
-R is used to change permission to directory and its contents
What is a softlink and how to create it?
A softlink is like a shortcut in windows.
Create it with ln -s original_file shortcut_file
Changes to softlinks apply to original file?
Yes
What happens to soft links when you delete their original file?
They have no use..
Can you have a softlink for directories?
Yes
How to create hardlinks?
ln sourcefile hardlinkname
ls -l shows the number of softlinks or hardlinks?
Number of hardlinks
Can you create hardlink for directories?
No.
Should you use absolute path or relative when creating links?
According to giatrakos, absolute path
If you have an original file and a hardlink, what happens when you delete the original file?
You can still access the original data through the hardlink.
What fits to the ?
find -type ? -name “file*”
? can be f if you want files whose name start with “file”
? can be d if you want directories …
if no type set then find command returns everything
find -type f -perm 701 -name “file*”
find files with perm rwx—–x and name prefix file
Whats the use of []?
Regex like [a-Z] or [abcd] etc
Whats the use of {}?
echo file{1..10..2} will create file1 file3 file5 … file10
Whats the usage of tee command?
tee file1 file2…
Takes input from stdin and outputs to each file (file1, file2..) and to the stdout
For example if you want to echo a message and log it to a logfile tee would be a way to go
How to use “more”
spacebar -> next page
b -> previous page
enter -> next line
q -> exit
Whats the main advantage of less against more?
Less doesn’t have to load the whole input file at once so it’s the way to go for big files.
grep -n “Stat” sample_data/
Search whole directory for line matches containing Stat
-n will return the line number of each match
!grep -r “Stat” sample_data/
Search subdirectories recursively
!grep -l “Stat” sample_data/
Instead of returning line numbers return the filenames that you found the match
!grep -w “Census” sample_data/README.md
search for a specific word
-cw would return the number lines that match
-cvw return the number of lines that didnt match
Defaults about sort command?
delimiter is considered whitespace
sorts alphabetically, not numerically
What’s the use of cp -R (equivalent to cp -r)
Use -R to copy entire directory with its contents
mv -i
cp -i
What’s the use of -I flag?
With -I those commands will prompt you before proceeding, so you make sure that you don’t override any preexisting files
chmod a=rw file.txt
all: owner, group,others = rw permissions
usermod -a -G my_group newperson
Add new user to the new group
usermod -g my_group newperson
change the primeary group of the user
mkdir testchown
touch ./testchown/file.txt
chown -R newperson testchown
newsperson is the user of the testchown directory and its contents like file.txt
!find . -type f -perm 701 -print -exec chmod 644 {} \;
In current directory find all files with permissions 701 and change their permissions to 644. Its common to use exec for this use case
!find . -user root -iname “*.JSON”
in current directory find files where user owner is root and name ends in .json case insensitive
!find -L /content -samefile testchmod/myfile.fd
find softlinks and hardilnks of my file.fd under testchmod
!grep -w “Census” sample_data/README.md
Search for a distinct word Census.
wc -c
write total number of bytes
wc -m
write the total number of characters
sort -r +2 file.txt
sort in reversed alphabetical order and the key is the third column
!sort -t” “ -k 3.3,3.5 sortmylines.txt
delimiter = “ “
Start sorting from 3d char of 3d field till 5th char of 3d field
!sort -c sortmylines.txt
check if a file is already sorted
cut -f2-3 -d” “ sortmylines.txt
show from 2 until 3d column
if it was -f2-5 would show column2,3,4,5
equivalent would be -f2,3
