JPoz  
     

Terminal Getting Started

Apr 6 2014

I pretty much do everything in the my terminal now, but when I was starting my developer journey I hated the command line. So for anyone that was like me and hates the command line here are some tips to get your over the hump and start loving the power of the command line.

Basics

Before we get into commands you need to know a couple of basics:

  • To stop any command use control-c. Some will stop on their own but this is the general way to stop any command in the terminal.
  • Arguments and flags. To control our commands we've got two tools: Arguments that we pass to the command and flag (or switches) to tune functionality of the command. Lets look at an example:
ls -l project_dir

Above we have one flag -l and one argument project_dir.

  • How to try this stuff out: Open up your “Terminal” app in the Utilities folder of your Application directory.
# This stuff is a comment about the command below
echo "This is a command you can copy and paste into your Terminal"

cd

Moving around is the first thing you'll need to be able todo and cd or change directory is your friend.

# given no arguments cd will take you to your home directory
cd

# ~ is also an alias for your home directroy
cd ~

# moves into your Downloads folder that is in the current directory
cd Download

# moves into the Downloads folder that is inside the current directory
# Having the ~/ in the front means this is an absolute path meaning it
# will move to the same directory no matter what the current directory is
cd ~/Downloads

# Having the path start with / also makes it an absolute path from the "root"
# or base of our machine.
# This will move into our Utilities folder no matter what the current directory is
cd /Applications/Utilities

For more information on cd checkout the wikipedia page on the cd command.

ls

Now that you're in the directory you want to be what's in there? That where ls comes in. The ls command lists directory contents.

# ls with no parameters list the directory you are currently in
ls

# Often you'll want to see the "hidden" files in a directoy.
# Adding the -a flag will show all files
ls -a

# Need to know who owns a file? Maybe who can read or write to it?
ls -al

pwd

Now that you're moving around let make sure you can check where you are. The pwd command prints out your working/current directory.

# pwd will print out which directory you are currently in
pwd

mkdir

Lets make some new folders on your computer. With the mkdir command you can make new directories.

# give mkdir the folder you'd like to create as the first parameter
mkdir my_new_folder

cat

I've found my file! Now what's in it? Meow meet cat aka the concatenate command. Pretty simple just takes a file an puts it on the standard output.

# cat a file
cat /etc/hosts

tail and head

OMG logs are the worst and the best all at once. When you don't want the full file use tail to get just a part from the end and head to get a part from the beginning.

# tail with the -f flag will wait for additional
# data to be added on to the file. Try out the command below to watch your wifi
# connectivity. Try turning on and off your wifi when its running
tail -f /var/log/system.log

# head is the opposite. To just get the first line of a file try:
head -n 1 /var/log/system.log

| “pipe”

Sometimes one command isn't enough. The | character aka “pipe” allows us to take the output of one command and feed it into the next. We'll use this in the next section with grep.

grep

Ah grep. I use this command so much sometimes I use it as a verb in sentences: “Oh just grep out of the value.” as in “Oh just search and return the value”

# grep can be used to search for text within
# a file:
grep apple /var/log/system.log

# We can also use grep to search whole directories of files
# Adding the -r recursivly searches the directores for files including the
# given text. Below we search our Documents directory for passwords :)
grep -r password ~/Documents

# grep can also be used with | aka pipe. This allows us to search the output of
# other commands. We can tail -f and grep the results:
tail -f /var/log/system.log | grep apple

cp

Copying files is useful. Use cp to copy files or whole directories.

# make a duplicate of a important file
cp my_journal.txt copy_my_journal.txt

# Notice the -r or recusive flag. This will duplicate the Documents folder and everything inside it
cp -r ~/Documents ~/Documents_copy

Other helpful tips:

  • Using the up and down arrows you can cycle through the histroy of your commands.
  • Use open . to open your current directory in the Finder.
  • Hit Tab as much as you can. It auto completes for you.