def do_cd(self, line):
#error handling ensures wrong directory path or permission denial will not crash shell
try:
if self.home in line:
os.chdir('/' + line)
else:
os.chdir(os.getcwd() + '/' + line)
except FileNotFoundError:
print(Colours.red("Invalid directory: {}".format(line)))
except Exception as e:
print(e)
#update the prompt to show the new directory
cmd.Cmd.prompt = Colours.cyan('(KarlShell:') + Colours.pink(
os.getcwd() + ') ')
class MyShell(cmd.Cmd):
shell = os.environ['PWD']
cmd.Cmd.intro = "Hello and welcome to KarlShell! (V1.3.1 running from {})".format(
shell)
cmd.Cmd.prompt = Colours.cyan('(KarlShell:') + Colours.pink(os.getcwd() +
') ')
dirs = os.getcwd().split('/')
home = dirs[1]
#changes the directory
#is designed to take either the full path starting from the home directory e.g. /home/user/Documents, or take a single subdirectory of the cwd e.g. /Documents
def do_cd(self, line):
#error handling ensures wrong directory path or permission denial will not crash shell
try:
if self.home in line:
os.chdir('/' + line)
else:
os.chdir(os.getcwd() + '/' + line)
except FileNotFoundError:
print(Colours.red("Invalid directory: {}".format(line)))
except Exception as e:
print(e)
#update the prompt to show the new directory
cmd.Cmd.prompt = Colours.cyan('(KarlShell:') + Colours.pink(
os.getcwd() + ') ')
#displays current working directory
def do_pwd(self, line):
print(os.getcwd())
#lists and displays all subdirectories and files
# if redirect is True, pass output onto output_redirect method
def do_dir(self, line):
if self.check_redirect(line) == False:
print("\n".join(os.listdir()))
else:
out = ("\n".join(os.listdir()))
self.output_redirect(line, out)
#lists and displays environmental strings
def do_environ(self, line):
if self.check_redirect(line) == False:
for k, v in os.environ.items():
print(k + ": " + v)
else:
out = []
for k, v in os.environ.items():
out.append(k + ": " + v)
out = "\n".join(out)
self.output_redirect(line, out)
#outputs the argument supplied by user
def do_echo(self, line):
tokens = self.get_tokens(line)
if self.check_redirect(line) == False:
print(line + '\n')
else:
out = (' '.join(tokens[0:-2]))
self.output_redirect(line, out)
#opens manual located in readme file and displays to user twenty lines at a time
def do_help(self, line):
try:
if self.check_redirect(line) == False:
with open(self.shell + "/readme", "r") as f:
i = 2
j = 22
help_lines = f.read().split("\n")
next_twenty = '\n'.join(help_lines[i:j])
while j < len(help_lines):
next_twenty = '\n'.join(help_lines[i:j])
print(next_twenty)
input()
i += 20
j += 20
else:
with open(self.shell + "/readme", "r") as f:
out = f.read()
self.output_redirect(line, out)
except:
(print("There appears to be a problem with the help manual..."))
#clears the display by checking terminal size and printing new lines
def do_clr(self, line):
rows, columns = os.popen('stty size', 'r').read().split()
for i in range(0, int(rows)):
print("\n")
#pauses operation of the shell until enter is pressed
def do_pause(self, line):
input("Press enter to resume..." + "\n")
#an extra internal command I added to help with testing
def do_sleep(self, line):
try:
time.sleep(int(line))
except:
print("Exception!")
#exits the shell
def do_quit(self, line):
sys.exit()
#default action for when user inputs an empty line
def emptyline(self):
print("")
#default action for commands that are not defined
def default(self, line):
tokens = self.get_tokens(line)
if tokens[-1] == "&":
self.background_exec(line)
else:
self.invoke(line)
#if user enters a command that is not among the internal commands, check if the command is invocation of external programs and execute them
def invoke(self, line):
line = self.get_tokens(line)
pid = os.fork()
if pid > 0:
wait_pid = os.waitpid(pid, 0)
else:
try:
os.execvp(line[0], line)
except FileNotFoundError:
print(
Colours.red(
" '{}' not found. Type 'help' for shell documentation."
.format(' '.join(line))))
self.do_quit('')
except:
print("Exception!")
self.do_quit('')
#execute program defined in line as background process
def background_exec(self, line):
line = self.get_tokens(line)
subprocess.Popen(line)
#check if user is attempting to redirect output
def check_redirect(self, line):
tokens = self.get_tokens(line)
if len(tokens) > 0 and (">" in tokens or ">>" in tokens):
return True
else:
return False
#determine whether user wants to append or truncate and find position of new file name
def output_redirect(self, line, output):
tokens = self.get_tokens(line)
i = 0
while i < len(tokens) and (tokens[i - 1] != ">"
or tokens[i - 1] != ">>"):
if tokens[i] == ">":
self.truncate(line, output, i)
elif tokens[i] == ">>":
self.append(line, output, i)
i += 1
#get name of new file by using position supplied by output_redirect, and either create new file or truncate existing
def truncate(self, line, output, position):
i = position
tokens = self.get_tokens(line)
with open(tokens[i + 1], "w") as f:
f.write(output)
#same as truncate method, except append to existing file
def append(self, line, output, position):
i = position
tokens = self.get_tokens(line)
with open(tokens[i + 1], "a") as f:
f.write("\n" + output)
#a simple method for splitting a line into tokens
def get_tokens(self, line):
tokens = line.split()
return tokens
