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Implementation of head using docopt
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| """ | |
| Usage: head [options] [FILE]... | |
| -c K, --bytes=K print the first K bytes of each file; | |
| with the leading `-', print all but the last | |
| K bytes of each file | |
| -n K, --lines=K print the first K lines instead of the first 10; | |
| with the leading `-', print all but the last | |
| K lines of each file [default: 10] | |
| -q, --quiet, --silent never print headers giving file names | |
| -v, --verbose always print headers giving file names | |
| --help display this help and exit | |
| --version output version information and exit | |
| """ | |
| import sys | |
| from collections import namedtuple | |
| import docopt | |
| HeadParams = namedtuple("HeadParams", "version bytes lines print_header files") | |
| def err(msg): | |
| sys.stdout.write("head: {0}\n".format(msg)) | |
| sys.exit(1) | |
| def get_params(args): | |
| try: | |
| bytes = int(args["--bytes"]) if args["--bytes"] else None | |
| except ValueError: | |
| err("invalid value for bytes") | |
| try: | |
| lines = int(args["--lines"]) if args["--lines"] else None | |
| except ValueError: | |
| err("invalid value for lines") | |
| silent = args["--silent"] | |
| verbose = args["--verbose"] | |
| version = args["--version"] | |
| files = args["FILE"] | |
| if not files: | |
| files.append("-") | |
| print_header = True | |
| if len(files) == 1: | |
| print_header = False | |
| if silent: | |
| print_header = False | |
| if verbose: | |
| print_header = True | |
| return HeadParams(version, bytes, lines, print_header, files) | |
| def print_one_head(fp, params): | |
| if params.print_header: | |
| sys.stdout.write("==> {0} <==\n".format(fp.name)) | |
| if params.bytes: | |
| sys.stdout.write(fp.read()[:params.bytes]) | |
| else: | |
| sys.stdout.write("".join(fp.readlines()[:params.lines])) | |
| def head(): | |
| args = docopt.docopt(__doc__) | |
| params = get_params(args) | |
| if params.version: | |
| print("head version: 1.0.0") | |
| return | |
| for filename in params.files: | |
| try: | |
| if filename == "-": | |
| print_one_head(sys.stdin, params) | |
| else: | |
| with open(filename) as fp: | |
| print_one_head(fp, params) | |
| except IOError as e: | |
| err("error opening {0}: {1}".format(filename, e)) | |
| if __name__ == "__main__": | |
| head() |
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