Implementing cat with a python script.

Author: SaraTahir28

implement-shell-tools/cat/cat.py

@@ -0,0 +1,62 @@
+import argparse
+import sys
+import glob # to find file paths and match patterns
+
+
+
+def parse_args():
+    parser = argparse.ArgumentParser(
+        prog = "cat",
+        description= "copying cat commands behavior with -n and -b flags"
+    )
+    parser.add_argument("-n", "--number", action="store_true", help="Number all output lines")  #with store true argument behaves like a boolean, flag present returns true, not present = false.
+    parser.add_argument("-b", "--number-nonblank", action="store_true", help="Number non-empty output lines")
+    parser.add_argument("files", nargs="+", help="Files to read (supports shell globs)") # accepts one or more files names or glob patterns.
+    return parser.parse_args()
+
+#Uses glob to expand patterns like *.txt.
+def expand_files(patterns):
+    expanded = []
+    for p in patterns:
+        matches = glob.glob(p)
+        if matches:
+            expanded.extend(sorted(matches))  # predictable order
+        else:
+            print(f"cat: {p}: No such file", file=sys.stderr) #Prints an error if a pattern matches nothing.
+    return expanded
+
+def cat_file(filename, number_all=False, number_nonempty=False):
+    try:
+        with open(filename, 'r') as f:
+            lines = f.readlines()
+    except FileNotFoundError:
+        print(f"cat: {filename}: No such file")
+        return
+#Applies numbering rules depending on flags.
+    line_num = 1
+    for line in lines:
+        line = line.rstrip('\n')
+        if number_all:
+            print(f"{line_num:6}  {line}")
+            line_num += 1
+        elif number_nonempty:
+            if line.strip():
+                print(f"{line_num:6}  {line}")
+                line_num+= 1
+            else:
+                print(line)
+        else:
+            print(line)
+
+def main():
+    args = parse_args() #return an args obj
+    files = expand_files(args.files) #list of filenames or patterns user typed passed to expand_files helper that uses glob module to expand patterns to actual file paths
+    if not files:
+        sys.exit(1)  #programs exits with status code 1- signals and error if no files were found
+
+#looping through each file path on expanded list
+    for file in files: 
+        cat_file(file, number_all=args.number, number_nonempty=args.number_nonblank)
+
+if __name__ == "__main__":
+    main()