mysh - A very simple shell

This is a very simple shell built for NCTU Advanced Unix Programming course.

What are supported

• Built-in commands
  • cd: change current working directory
  • exit: terminate the shell
  • export: set environment variable
  • unset: unset environment variable
  • jobs: list all current jobs
  • fg: put a job to foreground
  • bg: put a job to background
  • kill: kill a job
• Run any Unix programs either in foreground or background (&)
• Ctrl-C and Ctrl-Z signal handling
• Standard input/output redirection operators: < and >
• Create pipeline using pipe operator: |
• Filename expansion with * and ? operators
• Job control support: Ctrl-Z, jobs, fg, and bg

[Important] Our parser does not recognize quotation marks as special characters; therefore, the command echo "124 456" will have output "123 456", but not treat "123 456" as a single argument and show 123 456.

Environment Variables

Usage

mysh> export KEY=value
mysh> unset KEY

Example

hungys in /Users/hungys/Workspace/UnixCourse/HW/hw3
mysh> export TEST=mysh
hungys in /Users/hungys/Workspace/UnixCourse/HW/hw3
mysh> printenv TEST
mysh
hungys in /Users/hungys/Workspace/UnixCourse/HW/hw3
mysh> unset TEST
hungys in /Users/hungys/Workspace/UnixCourse/HW/hw3
mysh>

Filename Expansion

Usage

We accept the basic regular expression syntax: * and ? to expand pathnames matching the pattern.

Example

hungys in /Users/hungys/Workspace/UnixCourse/HW/hw3
mysh> ls *
Makefile    mysh        mysh.c      mysh.o
hungys in /Users/hungys/Workspace/UnixCourse/HW/hw3
mysh> ls mysh*
mysh    mysh.c  mysh.o
hungys in /Users/hungys/Workspace/UnixCourse/HW/hw3
mysh> ls *.c
mysh.c
hungys in /Users/hungys/Workspace/UnixCourse/HW/hw3
mysh> ls m?sh.?
mysh.c  mysh.o
hungys in /Users/hungys/Workspace/UnixCourse/HW/hw3
mysh>

Job Control

[Important] The maximum number of background jobs is limited to 20 by default. (defined as NR_JOBS macro)

Usage

mysh> jobs   # list all jobs
mysh> fg %<job_id>
mysh> fg <pid>
mysh> bg %<job_id>
mysh> bg <pid>
mysh> kill %<job_id>
mysh> kill <pid>

Example

hungys in /Users/hungys/Workspace/UnixCourse/HW/hw3
mysh> sleep 30 &
[1] 2443
hungys in /Users/hungys/Workspace/UnixCourse/HW/hw3
mysh> sleep 60 &
[2] 2444
hungys in /Users/hungys/Workspace/UnixCourse/HW/hw3
mysh> jobs
[1] 2443    running sleep 30
[2] 2444    running sleep 60
hungys in /Users/hungys/Workspace/UnixCourse/HW/hw3
mysh> fg %1
[1] 2443    continued   sleep 30
^Z[1]   2443    suspended   sleep 30   # Press Ctrl-Z
hungys in /Users/hungys/Workspace/UnixCourse/HW/hw3
mysh> bg %1
[1] 2443    continued   sleep 30   # Continue to run Job 1 in background
hungys in /Users/hungys/Workspace/UnixCourse/HW/hw3
mysh> jobs
[1] 2443    continued   sleep 30
[2] 2444    running sleep 60
hungys in /Users/hungys/Workspace/UnixCourse/HW/hw3
mysh> kill %2
[2] 2444    terminated  sleep 60
hungys in /Users/hungys/Workspace/UnixCourse/HW/hw3
mysh>
[1] 2443    done    sleep 30   # Job 1 is finished in background

Notice that for the last case, "done" message will not show up until you execute command next time. The zombie processes will also be reaped at the same time.

Build and Run

mysh is implemented in pure C, and we have provided a simple Makefile.

To compile the source code, simply type make. Then you can execute ./mysh to launch the shell.