1.5 Getting around
1. A sense of location
Note
Always know where are you!
pwd
Now to the command itself. pwd is an abbreviation of “print working directory”. All it does is print out the shell’s current working directory. But what is a working directory?
One important concept to understand is that the shell has a notion of a default location in which any file operations will take place. This is its working directory. If you try to create new files or directories, view existing files, or even delete them, the shell will assume you are looking for them in the current working directory unless you take steps to specify otherwise. So it’s quite important to keep an idea of what directory the shell is “in” at any given time, after all, deleting files from the wrong directory could be disastrous. If you are ever in any doubt, the pwd command will tell you exactly what the current working directory is.
You can change the working directory using the cd command, an abbreviation for “change directory”.
cd /
Warning
Too many roots
Beware: although the / directory is sometimes referred to as the root directory, the word root has another meaning. root is also the name that has been used for the superuser since the early days of Unix.
Understanding what you’re running
Executing commands without understanding what they do, is the best way to fail. To get more information you can look at the help documentation or read the manual.
# Getting the documentation for the command
pwd --help
# Reading the manual
man pwd
What is here?
Executing commands in the terminal sometimes feels like searching for something in the dark. We need to get more information about the current location.
# List all the files and directories in the current location
ls
ls --help
# ls - command
# --help - argument
# think of the arguments as parameters input for functions
We rarely use simple ls, we use.
ls -l
# or
ll
ls -ltrha
# -l use a long listing format
# -t sort by modification time, newest first
# -r, --reverse reverse order while sorting
# -h, --human-readable with -l and -s, print sizes like 1K 234M 2G, etc.
# -a, --all do not ignore entries starting with.
Relative and absolute paths
Most of the examples we’ve looked at so far use relative paths. That is, the place you end up at depends on your current working directory. Consider trying to cd into the /etc folder. If you’re already in the root directory that will work fine:
cd /
# and
cd etc
# or
cd /etc
Finding home
linux_user@linux_machine:/$ cd /
linux_user@linux_machine:/$ pwd
/
linux_user@linux_machine:/$ cd home
linux_user@linux_machine:/home$ ls
total 12K
drwxr-xr-x 3 root root 4.0K Aug 25 12:49 .
drwxr-xr-x 12 linux_user linux_user 4.0K Oct 25 14:58 linux_user
drwxr-xr-x 19 root root 4.0K Nov 4 10:53 ..
Try out
# home of the user
cd ~
# Going back to the previous directory
cd -
# Moving one step closer to /, getting to a level up
cd ..
2. Creating your first directory
TODO:
Create 3 different directories:
dir1dir2dir3Remove the 2nd one:
dir2Remove the 1st and 3rd one:
dir1dir3Create a directory with subdirectories:
parent/child/grandchildRemove them:
parent/child/grandchild
# Change the directory to the home of the user
cd ~
# Create a new sandbox directory where we will work from now
mkdir sandbox
# Check that directory was created
ls -ltrha
# Change the directory to the
cd sandbox
# Creating multiple directories
mkdir dir1 dir2 dir3
# Removing directories
rmdir dir2
rmdir dir1 dir3
# To create a directory structure
mkdir -p parent/child/grandchild
mkdir --help
rmdir --help
rmdir -p parent/child/grandchild/
3. Pipe and Redirection
Redirection
Most shells offer the ability to alter the way that application input and output flows. This can direct output away from the terminal and into files or other applications, or otherwise read input from files instead of the terminal.
All applications have three unique streams that connect them to the outside world.
These are referred to as :
Standard Input, or stdin
Standard Output, or stdout
Standard Error, or stderr.
cd ~/sandbox
echo "This is a test"
echo just prints its arguments back out again (hence the name). But combine it with a redirect, and you have got a way to easily create small test files:
echo "This is a test" > test_1.txt
echo "This is a second test" > test_2.txt
echo "This is a third test" > test_3.txt
ls
# Create a list of the existing files
# > replace the content
ls > listOfFiles
# >> append to the content
ls >> listOfFiles
Reading files
# find out how to use the read file application
cat --help
# Getting the manual of the cat command
man cat
# Reading the content of multiple files
cat test*1.txt test*2.txt test_3.txt
# Reading the content of multiple files
cat test_?.txt
# Reading the content of multiple files
cat test_*
# Reading the content of multiple files and redirecting the output to a new file
cat t* > combined.txt
cat listOfFiles >> combined.txt
cat combined.txt
less combined.txt
Note
When you consider both case sensitivity and escaping, a good rule of thumb is to keep your file names all lowercase, with only letters, numbers, underscores, and hyphens. For files, there is usually also a dot and a few characters on the end to indicate the type of file it is (referred to as the “file extension”). This guideline may seem restrictive, but if you end up using the command line with any frequency you will be glad you stuck to this pattern.|
Redirecting Standard Error
On occasion, we need to redirect standard error instead of standard output. This works in the same way, but we need to specify the exact stream.
cat does-not-exist 2> log
Piping Between Applications
The final action that we can perform is to direct the output of one application into another one. This is commonly referred to as piping and uses the | operator instead
wc --help
man wc
ls | wc
wc -l combined.txt
uniq --help
man uniq
cat combined.txt | uniq | wc -l
sort combined.txt | uniq | wc -l
4. Moving and manipulating files
mkdir dir1 dir2
cp listOfFiles dir1
cp dir1/listOfFiles dir2
rm -rf dir1