Add `cut` command

[allureking]

Overview

This pull request introduces the cut command to our shell utilities, a powerful text processing tool used to extract sections from each line of input. The cut command implemented in this PR supports extracting specific fields or ranges of characters from each line, making it highly useful for parsing files and processing command output in scripts.

Implementation Details

Character Mode (-c): Extracts a specified range of characters from each line. Field Mode (-f) with Delimiter (-d): Extracts fields, which are text segments separated by a specific delimiter character.

Features Include: Character Range Extraction: Users can specify start and end positions to extract a range of characters from each line. Field Extraction: Users can extract one or more fields from each line, using a custom delimiter to define fields. Custom Delimiters: Supports single-character delimiters, including common ones like commas, colons, and spaces. Error Handling: Provides informative error messages for various error conditions such as invalid arguments or file read errors.

Usage

Extracting Character Ranges: cut -c start end [file] ex: cut -c 2 5 file.txt, echo hello | cut -c 1 5 Extracting Fields: cut -f field -d 'delimiter' [file] ex: cut -f 2 -d , file.txt, echo user:password | cut -f 2 -d :

[MessiBest07]

I can code review this one

[shooby-d]

I can code review this too😀

[shooby-d]

Code Review Comments

Output Testing

• -f and -d flags are only working with fixed positioning:

  $ echo "apple,banana,cherry" | cut -f 2 -d ,
  banana

  $ echo "apple,banana,cherry" | cut -d , -f 2
  cut: invalid arguments

This is what Unix cut produces with the same arguments:

echo "apple,banana,cherry" | cut -f 2 -d ,
banana

echo "apple,banana,cherry" | cut -d , -f 2
banana

fix/update suggestion: use a loop to iterate through the arguments and store the results in a struct, then access the flag fields through the struct.

• Good error checking for range that includes 0, also for exceeding line length when reading from a file.

Code check

• Be careful with the use of static buffers, but for this implementation I think you gave more than enough space.
• Helpful comments.
• In cutf you are doing i = 0 twice, you could probably do this once to clean up the code a little.
• You could make a helper function (maybe something like cut_error(char* err_msg)) for error handling that can replace the redundant fprintf(2, …) and exit(1) calls.

Other than these small things, looks like a good cut implementation!

[MessiBest07]

Code Review: Implementation of cutc and cutf functions Your cutc function is designed to extract content by character range, which is logically correct. However, if a file line exceeds MAX_LINE_LENGTH, the excess data is lost, which is a potential limitation. The cutf function also has the problem if the field content exceeds MAX_LINE_LENGTH.

In case you fail to process the open function, you can modify the code as follows： fd = (argc == 5) ? open(argv[4], 0) : 0; if (fd < 0) { fprintf(2, "cut: cannot open file %s\n", argv[4]); exit(1); }

Handling of multi-byte characters: If the input contains multibyte characters, the cut command handles them correctly. While this code is read and processed in bytes, it may be cut off in the middle of a character, resulting in a character encoding error or incomplete output (as mentioned above).

[malensek]

Looks great. In addition to the points above, you also need a doc file for this (it can be very simple). Code is clean and well commented (personally some of them I don't think are necessary but it does make it easy to follow!).