- To see what's in the file(first to last):
cat <location/filename> - To look at a file backwards, starting with the last line:
tac <location/filename> - To show the first 10 lines(default) of a file:
head <location/filename> - To show the first 'n' lines of a file:
head -n <location/filename> - To show the last 10 lines(default) of a file:
tail <location/filename> - To show the last 'n' lines of a file:
tail -n <location/filename> - To view documentation:
man <program name or command like python> - To gain root/administrative access(prompts for password):
sudo - To stop the graphical interface:
sudo systemctl stop gdm (or sudo telinit 3) - To start the graphical interface:
sudo systemctl start gdm (or sudo telinit 5) - To halt the system(requires superuser access):
shutdown -h - To reboot the system(requires superuser access):
shutdown -r - When administering a multi-user system, we have the option of notifying all users prior to shutdown:
sudo shutdown -h <time> "Message" - To find the address of an installed program:
which <app>orwhereis <app> - To display the print working directory:
pwd - To change the directory to home directory from the current working directory(current working directory replaces terminal's home directory in history):
cdorcd ~ - To go to parent directory of the current working directory:
cd .. - To go back to previous directory:
cd - - To list all the contents of working directory:
ls - To list all the contents including hidden files of working directory:
ls -a - To get the tree view of the filesystem(
sudo apt install treefor first time):tree - To get the tree view of only directories not files:
tree -d cdcommand remembers the moving history, to see the history:dirs- To push a directory in history for easy use:
pushd </foldername> - To delete the directory added recently from history:
popd - To create an empty file:
touch <filename> - To display and redirect ouput of a command:
tee - To create a new file from the terminal:
touch filename.extension - To create a new file with specific date(time: 24-hour format; LowerLimit of year: 1901):
- In string format:
touch -d "YYYY-MM-DD hh:mm:ss" filename.extension - In Integer-ish format:
touch -t YYYYMMDDhhmm.ss filename.extension
- In string format:
For example:
touch -d "2010-01-02 00:01:00" xyz.txt
touch -t 201001020001.00 xyz.txt
Both the above commands create a text file "xyz.txt" with creation date as 02-January-2010 at 12:01 a.m.
-
To create a directory/folder:
mkdir folderNameormkdir location/foldername -
To remove an empty directory:
rmdir folderName -
To remove a directory along with its contents:
rm -rf folderName -
To rename a file/directory:
mv FileName newFileName -
To remove a file:
rm fileName -
To forcefully remove a file:
rm –f -
To interactively remove a file(it asks if you're sure to delete or not):
rm -i -
To locate a file:
locate filename -
To list all files in the current directory and all of its subdirectories:
find -
To search for files and directories in a folder:
find /folder -name filename -
To search only for directories:
find /folderName -type d -name somethingToBeFound -
To search only for regular files:
find /folderName -type f -name somethingToBeFound- Commonly used options to shorten the list include:
- -name (only list files with a certain pattern in their name)
- -iname (also ignore the case of file names)
- -type (which will restrict the results to files of a certain specified type, such as d for directory, l for symbolic link, or f for a regular file, etc.)
- Commonly used options to shorten the list include:
-
To kill a process(you can only kill your own processes; those belonging to another user are off limits, unless you are root):
kill -SIGKILL <pid>orkill -9 <pid>. -
To see the processes running:
ps -auxorhtop -
To get task manager-ish view of processes running:
top -
To see the processes in tree-view:
pstree -
To display all jobs running in background(shows the job ID, state, and command name):
jobs -
To display all jobs running in background(adds the PID of the background jobs to normal jobs commands):
jobs -l -
To display information about mounted filesystems, including the filesystem type, and usage statistics about currently used and available space:
df -Th -
To compare two text files(for binary: replace with
cmp):diff [options] <file1> <file2>Options
-c: Provides a list of differences with 3 lines of context-r: Used to recursively compare subdirectories along with present directory-i: To ignore the case of letters-w: To ignore white spaces and tabs-q: To return only if files are different without listing differences
-
To compare three text files with one as reference:
diff3 <file1> <common-reference-file> <file3> -
To get the extension of a file:
file <fileName> -
To sync files between hosts:
rsync -
Two Ways to add lines to text:
- To add a line to a text file:
echo message>filename - To append the line to text file:
echo message2>>filename- Example(both ways do the same thing):
- echo message 1 > myfile
echo message 2 >> myfile
echo message 3 >> myfile - cat << EOF > myfile
> message 1
> message 2
> message 3
> EOF
Above both codes do the same:
message 1
message 2
message 3 - echo message 1 > myfile
- Example(both ways do the same thing):
- To add a line to a text file:
-
To get tutorial about vim (Vi IMproved):
vimtutor- Commands in vim editor:
- Start the editor and edit file:
vi filename - Start and edit file in recovery mode(recover file after a crash):
vi -r filename - Read in file and insert at current position:
:r fileName - Write to the file:
:w - Write out to file:
:w file - To overwrite file:
:w! file - To exit and write out modified file:
:xor:wq - To quit:
:q - To quit without saving:
:q! - To count the words in a file in vim editor:
:! wc % - To go from vim terminal to vim editor: press
i
- Start the editor and edit file:
- Commands in vim editor:
-
To identify current user:
whoami -
To identify all logged-on user:
who -
To retrieve currently defined aliases:
alias -
To define a new user:
sudo useradd <username> -
To delete a user:
sudo userdel <username> -
To temporary become a super-user:
su -
To view the files present in the current directory in the long listing format:
ls -l -
When working with compressed files, most associated utilities required to work have 'z' prefixed to their name:
- To view a compressed file:
zcat compress_file - To page through a compressed file(it's a filter):
zless compressed-fileorzmore compressed-file - To search inside a compressed file(-i ignores the case):
zgrep -i "whatever-you-want-to-search" compressed-file - To compare two compressed files: zdiff file1 file2
- To view a compressed file:
-
To sort the lines, according to the characters at the beginning of each line:
sort <filename> -
To combine the two files and sort the lines, then display the output to the terminal:
cat file1 file2 | sort -
To sort the lines in reverse order:
sort -r <filename> -
To sort the lines by the 3rd field on each line instead of the beginning:
sort -k 3 <filename> -
To sort the list with removed duplicates, only uniques:
sort -u <filename> -
To remove duplicate entries from multiple files at once:
sort file1 file2 | uniq > file3or sort -u file1 file2 > file3 -
To count the number of duplicate entries:
uniq -c filename -
To paste contents from two files in a table format(first line of first file will correspond to first line of second file in a row):
paste file1 file2 -
To paste contents from two files with a delimiter like dash(-)or colon(:)(For example: xyz-123, in this xyz is from first and 123 is from second):
paste -d "delimiter" file1 file2 -
If two files have a common column and you want to merge them in a single file:
join file1 file2 -
To split a text file into equal files of n lines(the 100 newfile names will be suffixed with xx which aa..ab..ac):
split -n "number of files to be splitted in" <file_that_needs_to_be_split> <newfile> -
Regex(REGular EXpression; used for searching a particular pattern):
- Match any single character:
. - Match a or z:
a|z - Match end of a line:
$ - Match beginning of a line:
^ - Match a preceding item 0 or more times:
*
- Match any single character:
-
To search for a pattern in a file and print all matching lines:
grep [pattern] <filename> -
To print lines that exclude a certain pattern:
grep -v [pattern] <filename> -
TO print the lines that contain the numbers 0 through 9:
grep [0-9] <filename> -
To print context of lines (specified number of lines above and below the pattern) for matching the pattern. Here, the number of lines is specified as n:
grep -C n [pattern] <filename> -
To convert lower case to upper case(tr stands for translate):
cat filename | tr a-z A-Z -
To display the number of lines:
wc -l filename -
To display the number of bytes:
wc -c filename -
To display the number of words:
wc -w filename -
To check the status of the remote host:
ping <hostname> -
To show current routing table:
route –norip route -
To add a static route:
route add -net addressorip route add -
To delete a static route:
route del -net addressorip route del -
To download a web-page:
wget <url> -
To read a web-page from terminal:
curl <url> -
To get the contents of a web page and store it to a file:
curl -o filename_to_be_saved url -
To copy a local file to a remote system in the command prompt:
scp <localfile> <user@remotesystem>:/home/user/ -
To make a shell script for easy automation, you need a .sh file
-
Functions in a script file:
function(){ echo "This is a sample function"} -
Syntax for if-else:
if [condition file];
then
statements
else
statements
fi -
Conditions for if:
- Checks if the file exists:
-e - Checks if the file is a directory:
-d - Checks if the file is a regular file (i.e. not a symbolic link, device node, directory, etc.) :
-f - Checks if the file is of non-zero size:
-s - Checks if the file has sgid set:
-g - Checks if the file has suid set:
-u - Checks if the file is readable:
-r - Checks if the file is writable:
-w - Checks if the file is executable:
-x
- Checks if the file exists:
-
Logical operators to be used with if[expression1 -operation expression2]:
- Equal to:
-eq - Not equal: `-ne
- Greater than:
-gt - Less than:
-lt - Greater than or equal to:
-ge - Less than or equal to:
-le - Compares the sorting order of string1 and string2:
[[ string1 > string2 ]] - Compares the characters in string1 with the characters in string2:
[[ string1 == string2 ]] - Saves the length of string1 in the variable myLen1:
myLen1=${#string1}
- Equal to:
-
Switch statement:
case expression in
pattern1) execute commands ;;
pattern2) execute commands ;;
pattern3) execute commands ;;
pattern4) execute commands ;;
* ) execute some default commands or nothing ;;
esac -
Three types of loops are often used in most programming languages:
forloop:
for variable-name in list
do
execute one iteration for each item in the list until the list is finished
donewhileloop:
while condition is true
do
Commands for execution
doneuntilloop; it repeats a set of statements as long as the control command is false:
until condition is false
do
Commands for execution
done
-
To edit/debug a script(to exit: write
+ exit 0at the end of file):script.sh debug -
To create a temporary file:
TEMP=$(mktemp /tmp/tempfile.XXXXXXXX) -
To create a temporary directory:
TEMPDIR=$(mktemp -d /tmp/tempdir.XXXXXXXX) -
To generate a random number:
$RANDOM -
To get the length of a string:
${#string}orexpr length $string -
Printing Operations:
- To print the file to default printer:
lp <filename> - To print to a specific printer (useful if multiple printers are available):
lp -d printer_id <filename> - To print the output of a program:
program | lp echo string | lp - To print multiple copies:
lp -n number <filename> - To set the default printer:
lpoptions -d printer - To show the queue status:
lpq -a - To configure printer queues:
lpadmin - To get a list of available printers, along with their status:
lpstat -p -d - To check the status of all connected printers, including job numbers:
lpstat -a - To cancel a print job:
cancel job-idORlprm job-id - To move a print job to new printer:
lpmove job-id newprinter
- To print the file to default printer:
-
To convert a text file to two columns (-2) formatted PostScript using the command(enscript is a tool that is used to convert a text file to PostScript and other formats):
enscript -2 -r -p psfile.ps textfile.txt -
To convert a text file to PostScript (saved to psfile.ps):
enscript -p psfile.ps textfile.txt -
To convert a text file to n columns where n=1-9 (saved in psfile.ps):
enscript -n -p psfile.ps textfile.txt -
To print a text file directly to the default printer:
enscript textfile.txt -
To convert a pdf to post-script:
pdf2ps file.pdforpdftops original.pdf converted_name.psorconvert original.pdf converted_name.ps -
To convert a post-script to pdf:
ps2pdf file.psorpstopdf original.ps converted_name.pdforconvert original.ps converted_name.pdf -
To merge the two documents first.pdf and second.pdf to output.pdf:
qpdf --empty --pages first.pdf second.pdf -- output.pdforpdftk first.pdf second.pdf cat output output.pdf -
To write only pages 1 and 2 of original.pdf to new.pdf:
qpdf --empty --pages original.pdf 1-2 -- new.pdforpdftk A=original.pdf cat A1-2 output new.pdf -
To rotate page 1 of original.pdf by 90 degrees clockwise to rotated.pdf:
qpdf --rotate=+90:1 original.pdf rotated.pdf -
To rotate all pages of original.pdf 90 degrees clockwise and save to rotate-all.pdf:
qpdf --rotate=+90:1-z original.pdf rotated-all.pdforpdftk A=original.pdf cat A1-endright output new.pdf -
To encrypt with 128 bits public.pdf with the passwd mypw with output as private.pdf:
qpdf --encrypt mypw mypw 128 -- public.pdf private.pdforpdftk public.pdf output private.pdf user_pw PROMPT -
To decrypt private.pdf with output as file-decrypted.pdf:
qpdf --decrypt --password=mypw private.pdf file-decrypted.pdf -
To open a pdf(evince is a pdf viewing GUI):
evince xyz.pdf -
CUPS interface is available at:
http://localhost:631