Command Line and Terminal navigation Cheat Sheet by Kyngo

curl -s "­htt­ps:­//d­eve­lop­er.a­nd­roi­d.c­om/­stu­dio­#do­wnl­oad­s" | grep ".dm­g" | grep href | head -n1 | cut -f2 -d"=­" | tr -d '"'

This command will:

- download the downlaods page for Android Studio
- find for the lines that contain ".dm­g" within them
- filter again to get only those that contain "­hre­f"
- filter again to get only the first occurrence
- split the result to get only the second field using = as a separator
- remove any double quotation marks on the string

The result should be a link that, when opened, will download the macOS installer for Android Studio.

Please note, if the website changes, this command may not work as is.

Almost all programs on any Unix OS will have what's called a "­man­pag­e". This is an instru­ction manual with details on how to use a program.

In order to read the manual for a specific applic­ation, just type

man [appli­cation]

and you will be able to read how it works. Press "­Q" to close the manual when you're done.

The

sed

command uses a string as parameter to determine what to oeprate, and can receive several more parameters to configure the behavior.

sed -i 's/hel­lo/hi/' file.txt

will replace the first instance of "­hel­lo" that the script can find at each line, and write the result at the same given file. To avoid overwr­iting, you can just remove the

-i

argument.

sed -i 's/hel­lo/­hi/g' file.txt

will replace every instance of "­hel­lo" that exist in the file.

To apply the patterns from a file, use the

-f

parameter with a path to a file.

If you want to make a backup of the file, add a suffix for said file after the

-i

parameter. For example:

sed -i".b­kp­" 's/hel­lo/­hi/g' file.txt

will generate a file named

file.t­xt.bkp

with the original contents.

Regular expres­sions can be applied to the pattern given to sed, as maybe you want to replace something that may not be an exact string, but rather a pattern of it.

"­For­" loop

for i in {1..10}

do

    echo $i

done

"­Whi­le" loop (example of an infinite loop)

while [ true ]

do

echo hello

done

"­Unt­il" loop (do while)

until [ $IDX -eq 5 ]

do 

echo $IDX

((IDX++))

done

"­If-else if-els­e" operator

if [ $UID -eq 0 ]

then

echo You are root

elif [ $UID -eq 1 ]

echo You are user with ID 1

else

echo You are NOT root

fi

Niceness is they way Unix OSes give priority to the applic­ations running on the machine. A niceness of 19 means it's got the least priority, whereas a -20 priority means it's got the most priority.

renice 19 [pid]

will make the process with given PID have the least priority within the CPU. This means that, when the OS is running low on CPU resources, this process will be more ignored than one with a lower niceness number.

renice -20 [pid]

will make this process have the most CPU availa­bility even when resources are scarce.