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This comprehensive review covers essential Linux/Unix utilities and command operations for IT244. It includes file and directory management using commands like ls, cp, mv, rm, and mkdir, along with text processing utilities such as cat, more, less, head, and tail. The review emphasizes the importance of access permissions, command execution in the foreground and background, and redirection techniques. Students will also explore variables, aliases, and process management. Mastering these topics is vital for a solid understanding of Linux/Unix systems.
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Midterm Review IT244 - Introduction to Linux / Unix Instructor: Bo Sheng
Basic Utilities • ls, cat, echo • ls –l, ls -a • cat file1 file2 file3 … • echo “hello world” > file • echo $VAR, echo hello*
Basic Utilities • more, less, head, tail • head -5 file • tail -3 file • pwd, cd • cp, mv, rm, mkdir, rmdir • ‘-i’ option • ‘-r’ option: rm –r dir1 • rmdiran empty directory
Basic Utilities • sort, wc, grep, |(pipe) • wc -l file, wc –c file • grep “keyword” file, grep -v • sort linux | head -5 • bzip2, gzip, tar (no compression)
Filename and Path • Hierarchical tree structure • Absolute path name • ls /home/it244/it244 • Relative path name • cd /home/it244 • ls it244 • ‘.’ ‘..’ ‘~’ • ‘*’ ‘?’ • echo hello*, echo ./.?a*
Access Permissions • r, w, x (chmod) • chmoda+rw file • chmod a=rx file • chmod 644 file • Execute permission of a directory • A directory is a table of files (filename:meta) • Executable means searchable
Access Permissions • Operations on book/book1 • ls book/book1 • book ( x ) • cat book/book1 • book1 ( r ), book ( x ) • rm book/book1 • book ( xw ), book1 ( w )
Links • Hard link and soft link • Hard link cannot refer to a directory • Soft link can point to a nonexistent file $ ln -s hello hello.sl $ rm hello $ echo “new” > hello $ cat hello.sl new
Execute Commands • Foreground and background jobs • command &, CTRL+Z • difference between a suspended job and a background job, PID • jobs, ps, kill, bg, fg • Group commands • (cmd1; cmd2; cmd3)
Processes • PID and PPID • sleep 10& • ps -f
Redirection • Standard input, output, error output • cat file1 file2 > out 2>err • cat file1 file2 &> out • cat file1 file2 > out 2>&1 • Redirected output will not be displayed on the screen.
Variables • System variables • $PATH, $PWD, $HOME • User defined variables • VAR=hello • export VAR=hello • declare; declare -x
Expansion/ Quote • Types • echo hello*; echo ~ • echo $VAR • echo $(pwd) • echo $((1+1)) • VAR=hello* • echo $VAR • Single quote suspends all expansions
Alias • Short names (commands) • alias rm=‘rm –i’ • alias ll=‘ls –l’ • alias mypwd1=“echo pwd is $PWD” • alias mypwd2=‘echo pwd is $PWD’
Questions • Assume there are 3 files: file1, file2, and file3. After executing the following commands, how many files are there and what are the contents? $ cp file1 file2 $ mv file2 file3 $ rm file2 • Assume there are two directories dir1 and dir2, and dir1 contains a subdirectory dir3, what’s the result of $ cp -r dir1 dir2
Questions • In command line, the order of command name and arguments can be changed as long as there is no ambiguous interpretation. We tried an example in class: ‘echo hello world > hello world’ generated a file ‘hello’ which contains ‘hello world world’. Now, if we execute “> echo echoecho” 1). What is the output: • Display “echo echo” • Create a file “echo echo” • Create a file “echo” which contains a line of “echo” • An error message of “command not found” 2). Which echo is the command name: a. The 1st b. The 2nd c. The 3rd
Questions • Which of the following commands displays the value of the present working directory: • $pwd • echo pwd • echo $(pwd) • pwd | echo
