London | 26-SDC-July | Raihan Sharif | Sprint 4 | implement shell tools python

implement-shell-tools/cat/cat.py

@@ -0,0 +1,93 @@
+import argparse
+import sys
+
+parser = argparse.ArgumentParser(
+ prog="a simple cat implementation",
+ description="cat command line tool with the -n and -b flags"
+)
+
+parser.add_argument("-n", action="store_true", help="number all output lines")
+parser.add_argument("-b", action="store_true", help="number non-empty output lines")
+parser.add_argument("paths", nargs="+", help="file path or paths", )
+
+args = parser.parse_args()
+
+# cat returns different error messages depending on the reason the path could be read
+def read_file(path):
+ """Returns (content, error_message). error_message is None on success"""
+ try:
+ with open(path, "r",) as f:
+ return f.read(), None
+ except FileNotFoundError:
+ return None, f"cat: {path}: No such file or directory"
+ except IsADirectoryError:
+ return None, f"cat: {path}: Is a directory"
+ except PermissionError:
+ return None, f"cat: {path}: Permission denied"
+
+
+# -b (number the non-empty lines) takes priority over -n (number all lines)
+# if both are present
+def format_lines(lines, number_all=False, number_nonempty=False):
+ """Returns a list of formatted output lines"""
+ output = []
+
+ if number_nonempty:
+ line_num = 0
+ for line in lines:
+ if line == "":
+ output.append("")
+ else:
+ line_num += 1
+ # {line_num:6} right justied number, length of at least 6
+ # {some_str:6} left justifed string, length fo at least 6
+ output.append(f"{line_num:6}\t{line}")
+ elif number_all:
+ for i, line in enumerate(lines, start=1):
+ output.append(f"{i:6}\t{line}")
+ else:
+ output = lines
+
+ return output
+
+
+# TODO: runner function to call read_file, and feed it into formatLines, then print
+def cat_file(path, number_all=False, number_nonempty=False):
+ """
+ Calls read_file -> format_lines -> prints formatted line. 
+ Returns True if file read successfully, else returns False
+
+ If failed to read file, prints error to stderr
+ """
+ content, error = read_file(path)
+ if (error):
+ print(error, file=sys.stderr)
+ return False
+
+ # splitlines automatically trims trailing empty lines
+ lines = content.splitlines()
+ for line in format_lines(lines, number_all, number_nonempty):
+ print(line)
+
+ return True
+
+
+def main():
+ # cat exits with error code 1 if any file read fails
+ file_error = False
+
+ for path in args.paths:
+ line_num = 1
+ is_success = cat_file(path, args.n, args.b)
+
+ if not is_success:
+ file_error = True
+
+ # if at any point, file reading failed file error is set to True, 
+ # and program exist with code 1 after all tasks completed
+ sys.exit(1 if file_error else 0)
+
+# ensures that main only runs when this file/module is directly executed
+# not when it is imported, for example, for automated tests
+if __name__ == "__main__":
+ main()

implement-shell-tools/ls/ls.py

@@ -0,0 +1,80 @@
+import argparse
+import sys
+import os
+
+parser = argparse.ArgumentParser(
+ prog="a simple version of ls",
+ description="ls command line tool which can accept 0 or more arguements" \
+ "and take -a and -1 flags")
+
+parser.add_argument("-a", action="store_true", help="show all files, including dot files")
+
+# can't store as an attribute of Namespace object, because 1 is not a valid python identifier
+# but can store under the name given in the dest argument. When working with this
+# parser, look for "opt_one", not "1".
+parser.add_argument("-1", dest="opt_one", action="store_true", help="show one file/directory name per line")
+
+# takes 0 more arguments, if none are given, sets "." as default value
+parser.add_argument("paths", nargs="*", help="file/directory path(s) to display", default=".")
+
+args = parser.parse_args()
+
+
+def get_dir_entries(path, aFlag=args.a):
+ # warning: listdir() prints current directory by default
+ entries = os.listdir(path)
+ entries = [".", ".."] + entries
+ entries.sort()
+
+ if (not args.a):
+ entries = [entry for entry in entries if not entry.startswith(".")]
+
+ return entries
+
+
+def print_entries(entries, onePerLineFlag = args.opt_one):
+ if (onePerLineFlag):
+ for entry in entries:
+ print(entry)
+ elif (len(entries) > 0):
+ for i in range(len(entries)-1):
+ print(f"{entries[i]}\t", end="")
+ print(f"{entries[-1]}")
+
+
+def main():
+ # file and directory paths are processed separately
+ # file_args = [arg for arg in args.paths if os.path.isfile(arg)]
+ # dir_args = [arg for arg in args.paths if os.path.isdir(arg)]
+
+ file_args = []
+ dir_args = []
+ invalid_args = []
+
+ # this is a simplication, it groups all errors under "invalid file"
+ # real ls would have different messages things like permission denied
+ # also bad because it makes two syscalls
+ for arg in args.paths:
+ if (os.path.isfile(arg)):
+ file_args.append(arg)
+ elif (os.path.isdir(arg)):
+ dir_args.append(arg)
+ else:
+ invalid_args.append(arg)
+
+ for arg in invalid_args:
+ print(f"ls: {arg}: No such file or directory", file=sys.stderr)
+
+ if (len(file_args) > 0):
+ print_entries(file_args)
+
+ for index, path in enumerate(dir_args, start=0):
+ if (len(args.paths) > 1):
+ if (index > 0 or len(file_args) > 0):
+ print("")
+ print(f"{path}:")
+ print_entries(get_dir_entries(path))
+
+
+if __name__ == "__main__":
+ main()

implement-shell-tools/wc/requirements.txt

@@ -0,0 +1 @@
+argparse