useless

Description

Solution

1. Step 1Inspect the script
   Running the script without proper arguments prompts you to “Read the code first.” View the bash source to learn it performs basic math operations.

   cat useless

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   Shell scripts are plain-text files containing sequences of shell commands. Unlike compiled binaries, their source code is always readable with cator a text editor - there's no compilation step to reverse. This transparency is both a feature (easy to audit) and a limitation (no obfuscation possible without an external binary).

   Bash scripts often use a shebang line at the top (#!/bin/bash) to specify the interpreter. The script's error message telling you to "Read the code first" is a metacommentary - the challenge is literally teaching you that reading source code is the right debugging approach. In CTF terms, source code review (white-box testing) is always preferable to black-box guessing when the source is available.

2. Step 2Read the manual
   The maintainer stashed the picoCTF flag at the bottom of the manual page. Simply run man useless and scroll to the end.

   man useless

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   man pages (manual pages) are the traditional documentation system for Unix/Linux programs. Every standard command has a man page accessible via man <command>. Man pages are written in troff/groff markup and displayed through a pager (usually less). They're organized into sections: 1 (user commands), 2 (system calls), 3 (library functions), 5 (file formats), 8 (system administration), etc.

   Custom programs can install their own man pages in /usr/local/share/man/ or /usr/share/man/. This challenge placed a man page for the useless script there, mimicking how real software is documented. The flag hidden at the bottom of the man page teaches you to always read documentation thoroughly - important context, warnings, or in this case flags, are often at the end.

   Navigating man pages: Man pages open in less by default. Key navigation:

   • Space or f - scroll forward one page
   • b - scroll backward one page
   • G - jump to the end (where the flag is)
   • g - jump to the beginning
   • /pattern - search for a pattern (e.g., /picoCTF)
   • q - quit

   Real-world significance: Hiding data inside documentation is a form of steganography by obscurity. In real penetration testing, reading all available documentation, comments, and metadata of a target system is called information gathering or reconnaissance - you never know what useful details (API keys, internal URLs, debug flags) might be left in plain sight inside docs and comments.

Flag

picoCTF{us3l3s...it3d_4373}

No exploitation is required; just follow the hints inside the tool’s documentation.