Linux Basics

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Unix/Linux

They are designed to support the need of programmers. They are a powerful class of operating systems, multiuser, unified file system that names files and directories, heavily based on command-line interface called the "shell". They are designed to automate tasks. Put in upfront effort to reduce the manual effort needed later, called "long-term lazy" (slower to learn, faster to use).

Directory means the same thing as folder. All files and directories are referred to names called "paths".

  • ~ denotes the home directory of your account
  • . denotes the current directory
  • .. denotes the parent directory (one level up from current)
  • When you log into ugrad, you'll be in your home directory.

Connecting to ugrad from your own computer

Windows: download PuTTy, set Host Name as ugradx.cos.jhu.edu, type account name (JHED), and password. Mac: open Terminal, then type the command ssh <your-username>@ugradx.cs.jhu.edu Linux: open terminal and use ssh <your-username>@ugradx.cs.jhu.edu.

Command Line

Unix/Linux commands are case-sensitive. Learn Unix/Linu command line from this boot camp.

Basic Commands

  • pwd - print working directory
  • ls - list directory contents
  • cd <folder_name> - change directory [specify directory name]
  • mkdir <folder_name> makes a new directory within current directory.
  • less <file_to_view> view text file screenful at a time.
  • mv <source> <destination> changes the location of file or folder.
  • cp <source> <destination> make a copy file or folder.
  • rm <file_to_remove> remove a file. Not easy to undo deletion.
    • Use the flag -r to delete recursively and remove subdirectories and -i if you want to verify deletion.
  • Loations can be relative to current directory (E.g.: cp Hello.c folderForToday/hello.c) or absolute, based on the full path in file system.
  • exit logs out of the ugrad system.
  • man is the manual available at command line. Using with an operation or function gets details (e.g, man cp or man ispunct).

Copying Files

cp command in Unix is how we copy files within one machine. scp and pscps command is secure copy, a way to transfer copies from one machine to another.

In Mac Terminal or Windows Power Shell, use scp <source> <destination>.

In Windows with PuTTY, use pscp <source> <destination> in Command Prompt.

  • Note that Windows machine use backslash (\) instead of forward slash (/) used in unix for file paths.

Ugrad to Local

scp <username>@ugradx.cs.jhu.edu:<filename>.c .

(in Mac Terminal or Windows Power Shell).

For example,

scp ltran29@ugradx.cs.jhu.edu:HW1/file.c xyz/

Zipping

zip zipped_files.zip file1.c file2.c gitlog.txt

Packs up three files into a zipped_files.zip.

To confirm that it contains what you want,

unzip -1 zipped_files.zip

To unpack the zip file (i.e., extract its file),

unzip zipped_files.zip

Move and unpack in a new/different folder to avoid overwriting the original files.

I/O Redirection

When executing a command that produces output, redirect the result to a textfile (instead of on screen) by using '> outfile':

ls > myfiles.txt

When executing a command that takes input, redirect input from a plain txt file by using '< infile':

less < infile.text

Use both at once, or use a pipe command '|' to send the standard output of one command directly into standard inputfor another command. For example, to list your files but view the list one screenful at a time use:

ls | less
  • echo 4 | ./a.out sends an input directly into a program.

Homework workflow

  1. Write code, compile, test, and edit while continuously adding, committing, and pushing changes to personal git repo.
  2. Generate gitlog.txt file to document your commits using git log > gitlog.txt.
  3. Bundle files for submission with zip hw0.zip file1.c file2.c gitlog.txt.
  4. Confirm that your zip files contains everything with unzip -1 hw0.zip.
  5. Transfer the bundle onto local machine using scp <username>@ugradx.cs.jhu.edu:<HW0/hw0.zip .
  6. Upload hw0.zip to Gradescope. Wait for feedback and resubmit (only last one is graded).

Tips

  • *: wildcard character, helpful with file commands.
    • git add *.c* adds all files ending in .c to your staging area.
    • ls f* lists all files that start with f.
  • ! (bang): repeats the prior command. Can be used alone or with a start of a command name.
    • ! ! will execute the prior command.
    • !em will execute the most recent command that started with "em"
  • up and down arrows cycles through your command history
  • tab will complete command.
  • history | grep <keyword>: searches history with keyword.

Linked from Intermediate Programming