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", encoding="utf-8") 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, line_num, number_all=False, number_nonempty=False):
+    """Returns a list of formatted output lines"""
+    output = []
+    if number_nonempty:
+        for line in lines:
+            if line == "":
+                output.append("")
+            else:
+                # {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}")
+                line_num += 1
+    elif number_all:
+        for _, line in enumerate(lines, start=1):
+            output.append(f"{line_num:6}\t{line}")
+            line_num += 1
+    else:
+        output = lines
+
+    return output
+
+
+def cat_file(path, line_num, 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 -1
+
+    # splitlines automatically trims trailing empty lines
+    lines = content.splitlines()
+    for line in format_lines(lines, line_num, number_all, number_nonempty):
+        print(line)
+
+    return len(lines) + line_num
+
+
+def main():
+    # cat exits with error code 1 if any file read fails
+    file_error = False
+
+    line_num = 1
+    for path in args.paths:    
+        result = cat_file(path, line_num, args.n, args.b)
+        if result < 0:
+            file_error = True
+
+        if result > 0:
+            line_num = result
+
+    # 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/wc.py

@@ -0,0 +1,68 @@
+import argparse
+import sys
+import os
+
+# TODO: decompose into functions to make it more modular and reusable
+
+parser = argparse.ArgumentParser(
+    prog="a simple version of wc. Takes in one or more files.",
+    description="ls command line tool which can accept -l -w -c cflags")
+
+parser.add_argument("-l", action="store_true", help="show line count")
+parser.add_argument("-w", action="store_true", help="show word count")
+parser.add_argument("-c", action="store_true", help="show byte count")
+
+parser.add_argument("paths", nargs="*", help="file(s) for which to show data")
+
+args = parser.parse_args()
+
+totals = {"l": 0, "w": 0, "c": 0}
+
+# if no flags then set all flags to true, same as in real wc
+if (not args.l and not args.w and not args.c):
+    args.l = args.w = args.c = True
+
+for path in args.paths:
+    if (not os.path.exists(path)):
+        print(f"wc: {path}: open: No such file or directory", file=sys.stderr)
+    elif (os.path.isdir(path)):
+        print(f"wc: {path}: read: Is a directory", file=sys.stderr) 
+    elif (os.path.isfile(path)):
+        output_str = ""
+        with open(path, "r", encoding="utf-8") as file:
+            content = file.read()
+
+            lines = content.split('\n')
+
+            if (args.l):
+                line_count = content.count('\n')
+                totals["l"] += line_count
+                output_str += f"{line_count:8}"
+
+            if (args.w):
+                word_count = len(content.split())
+                totals["w"] += word_count
+                output_str += f"{word_count:8}"
+
+            if (args.c):
+                bytes = os.path.getsize(path)
+                totals["c"] += bytes
+                output_str += f"{bytes:8}"
+
+        output_str += f" {path}"
+        print(output_str)
+
+if (len(args.paths) > 1):
+    res = {key : val for key, val in totals.items() 
+           if val != 0}
+    total_str = ""
+    for v in res.values():
+        total_str += f"{v:8}"
+
+    total_str += " total"
+    print(total_str)
+
+
+
+
+