dksh: a rudimentary shell

This repository is inspired by Yash: Yet another shell

'dksh' is a rudimentary shell which supports common Linux commands such as 'grep', 'ls', 'cat', 'wc' and so on.

Till now, it has 24 built-in commands (and the number is still going up).

The goal of this project is to show the basics of Linux system programming.

Hopefully, 'dksh' will grow into a possible substitution for Bash.

dksh commands:

1. ls (-a -d -i -l | -adil)
2. echo ($?)
3. cat (-n -b -s | -nbs)
4. mkdir
5. rmdir
6. rm
7. cd (-)
8. chmod
9. pwd
10. wc (-)
11. date
12. exit (Ctrl-D)
13. help
14. kill (-signum)
15. who
16. history
17. more
18. grep (-v -n -c -H -h -i -o -q -b -L -l -m <num> --label <LABEL> | -vncHhioqbLl -m <num> --label <LABEL>)
19. mv
20. tee (-a)
21. time
22. dcl
23. undcl
24. sleep <NUMBER>
25. ./<user's program>

(PS. Putting a '-' before a command will call the Bash built-in commands.)

Special Characters

1. '&': background

Compile:

This repository, which is compatible with ANSI C, has been tested on CentOS, Ubuntu and macOS.

1. make (generate the target 'dksh')
2. make debug (generate the target 'dksh', with debug info)
3. make clean (delete the target 'dksh')

Manual:

1. ls:
    (1) ls <directory(ies) | file(s)>
    (2) ls -a <directory(ies) | file(s)>: including the hidden files
    (3) ls -d <directory(ies) | file(s)>: do not scan the directory, merely print
    (4) ls -i <directory(ies) | file(s)>: show inode
    (5) ls -l <directory(ies) | file(s)>: show details

2. echo:
    (1) echo <string(s)>
    (2) echo $?: show the return value of the last command

3. cat:
    (1) cat <file(s)>
    (2) cat -n <file(s)>: number the output lines, starting at 1
    (3) cat -b <file(s)>: number the non-blank output lines, starting at 1
    (4) cat -s <file(s)>: squeeze multiple adjacent empty lines

4. mkdir:
    (1) mkdir <directory>

5. rmdir:
    (1) rmdir <directory>

6. rm:
    (1) rm <file>

7. cd:
    (1) cd: chdir to $HOME directory
    (2) cd <directory>
    (3) cd -: chdir to the last directory

8. chmod:
    (1) chmod <mode (such as 664)> <file>

9. pwd:
    (1) pwd

10. wc:
    (1) wc: read from STDIN
    (2) wc -: read from STDIN
    (3) wc <file(s)>

11. date:
    (1) date

12. exit:
    (1) exit
    (2) Ctrl-D

13. help:
    (1) help: list the commands that dksh supports

14. kill:
    (1) kill <pid>: default signal is 15 (SIGTERM)
    (2) kill -<signum (such as 9)> <pid>: specify a signal

15. who:
    (1) who: show who is logged on

16. history:
    (1) history: show the commands that have been inputted

17. more:
    (1) more <file>: file perusal filter for crt viewing

18. grep:
    (1) grep <pattern> <file (if not specified, STDIN is used)>
    (2) grep -v <pattern> <file>: find the unmatched lines
    (3) grep -n <pattern> <file>: show the line number
    (4) grep -c <pattern> <file>: only a count of selected lines is written to standard output
    (5) grep -H <pattern> <file>: always print filename headers with output lines
    (6) grep -h <pattern> <file>: never print filename headers (i.e., filenames) with output lines
    (7) grep -i <pattern> <file>: perform case insensitive matching
    (8) grep -o <pattern> <file>: prints only the matching part of the lines
    (9) grep -q <pattern> <file>: quiet mode: suppress normal output
    (10) grep -b <pattern> <file>: the offset in bytes of a matched pattern is displayed in front of the respective matched line
    (11) grep -L <pattern> <file>: only the names of files not containing selected lines are written to standard output
    (12) grep -l <pattern> <file>: only the names of files containing selected lines are written to standard output
    (13) grep -m <NUM> <pattern> <file>: stop reading a file after NUM matching lines
    (14) grep --label <LABEL> <pattern> <file>: display input actually coming from standard input as input coming from file LABEL
    (15) grep -vncHhioqbLlm <num> --label <LABEL> <pattern> <file>

19. mv:
    (1) mv <oldpath> <newpath>

20. tee:
    (1) tee <file (if not specified, STDIN is used)>
    (2) tee -a <file>: append mode rather than truncate mode

21. time:
    (1) time <command>: run programs and summarize system resource usage

22. dcl:
    (1) dcl: convert declaration to words

23. undcl:
    (1) undcl: convert word description to declaration

24. sleep:
    (1) sleep <NUMBER>: sleep for a specified number of seconds

25. ./<user's program>:
    (1) ./<user's program>

Todo:

1. support '>' (IO redirection, output)
2. support '>>' (IO redirection, output, append-only)
3. support '<' (IO redirection, input)
4. support '<<' (IO redirection, input, here document)
5. support '|' (pipeline)