Two Tasks: List Text-File Names Under ~/UnixCourse Recursive ✓ Solved

Two tasks: 1) List text-file names under ~/UnixCourse recurs

What command would you give to produce a listing of the names of all the text files (as absolute paths) in ~/UnixCourse or its subdirectories (possibly nested several layers deep) followed immediately by the first line of text within that file? E.g., to produce a listing looking like this: /home/yourname/UnixCourse/foo.txt When in the course of human development /home/yourname/UnixCourse/Quotations/bar.txt Curiouser and curiouser!

In particular, all files should be listed and absolute paths and solutions that add extraneous characters around the file name (e.g., << or ==>) are not correct. A robust approach uses find with -print0 and a loop to print path and first line (example):

find "$HOME/UnixCourse" -type f -name '*.txt' -print0 | while IFS= read -r -d '' f; do

printf '%s\n' "$f"


head -n 1 "$f"


done

What command would you enter to get a count of the number of sshd processes running on the machine where you are logged in?

Use a command that yields only the numeric count, without counting the command that does the filtering itself, e.g., ps -Af | grep -w [s]shd | wc -l.

Paper For Above Instructions

Introduction

The two computational tasks presented here are classic demonstrations of Unix philosophy: compose simple, specialized tools to perform complex tasks without reimplementing functionality. The first task asks for a reliable way to enumerate all text files beneath a directory tree and reveal the first line of each file, formatted in a precise, two-line-per-file pattern. The second task asks for a concise command to count a specific process instance (sshd) on the running system. These problems emphasize portability, correctness, and the ability to reason about pipelines and process management. Unix tools like find, head, and ps are designed to be combined; when used properly they enable powerful one-liners while remaining readable and maintainable (Kernighan & Pike, 1984; Shotts, 2012).).

Task 1: Finding text files and printing their first lines

Solution strategy and rationale. The objective is to locate all files ending with .txt within ~/UnixCourse and all of its subdirectories, produce their absolute path, and then emit the first line of each file. A robust approach relies on a recursive finder (find), a safe way to handle filenames that contain spaces or unusual characters (null-terminated records with -print0), and a simple reader loop to output the first line (head -n 1). This pattern is portable across modern Unix-like environments and aligns with the Unix principle of combining small, simple tools (Kernighan & Pike, 1984; Kerrisk, 2010).

Recommended command (explanation embedded):

find "$HOME/UnixCourse" -type f -name '*.txt' -print0 | while IFS= read -r -d '' f; do

printf '%s\n' "$f"


head -n 1 "$f"


done

Notes on correctness and style. The command prints an absolute file path for each matching file (assuming $HOME expands to an absolute path, which it does in typical shells). The subsequent head -n 1 prints only the first line of that file, preserving the exact line content rather than a trimmed or rewrapped version. By using -print0 and read -d '', the loop correctly handles file names containing spaces or special characters, avoiding common pitfalls associated with simple for loops or pipelines (GNU Core Utilities, 2023; Shotts, 2012).

Alternative approaches exist, including using -exec with printf or readlink -f to canonicalize paths. However, the presented pattern is widely portable and maintains a clean separation between locating files and extracting metadata (Kernighan & Pike, 1984; Love, 2013).

Related considerations. If absolute path guarantees are needed under unusual environments, one might wrap the path in realpath or readlink -f, keeping in mind variations across platforms (GNU Core Utilities, 2023). In production scripts, validating that head successfully reads a line or handling binary files that may contain non-text data can improve robustness (Sobell, 2010).

Task 2: Counting sshd processes

Solution rationale. The goal is to count the number of sshd processes currently running on the host without counting the command that performs the filtering itself. A common, portable pattern uses ps to list processes and a filtering step that does not include the grep process, enabling a clean numeric tally via wc -l. This approach is standard in systems administration and scripting (Nemeth et al., 2017; Kerrisk, 2010).

One robust command is:

ps -Af | grep -w [s]shd | wc -l

Why this works. The pattern [s]shd matches the string "sshd" but prevents the grep process itself from appearing in the results, because the character class [s] is a literal starting character for the grep process’s argument, whereas the running process list shows the literal string "sshd" within the process name. This trick is a longstanding convention in shell scripting to avoid false positives (Newham & Robbins, 2003; Robbins, 2005).

Alternative method. If portability across environments with different ps implementations is needed, one can rely on the command column “comm” or use awk to perform a more precise match, for example:

ps -eo comm | awk '$1 == "sshd" {c++} END {print c+0}'

Important caveats. On some systems, ps options and columns differ (e.g., BSD-style ps vs. GNU ps). In macOS, ps options and output differ from Linux; in such cases, consult the system’s man pages and adapt the filter accordingly (Nemeth et al., 2017; Kerrisk, 2010). Regardless of the approach, ensuring that the count is numeric and that the filtering step does not count itself remains central to correctness (Kernighan & Pike, 1984).

Discussion: broader context and best practices

These tasks illustrate core best practices in command-line problem solving: use composable tools, prefer explicit pipelines with clear separation of concerns, and rely on well-established conventions to handle edge cases (spaces in filenames, different process naming, etc.) (Kernighan & Pike, 1984; Shotts, 2012). The choice of -print0 and read -r -d '' is a pragmatic solution to a notoriously tricky edge case in scripting—filenames containing whitespace or unusual characters—without sacrificing performance or readability (GNU Core Utilities, 2023; Robbins, 2005).

From a learning perspective, these patterns reinforce the utility of combining simple utilities to achieve sophisticated results, a recurring theme in Unix pedagogy (Kerrisk, 2010; Sobell, 2010). They also highlight the importance of understanding tool semantics (e.g., what “absolute path” means in the context of find’s -print0 versus -printf) and of testing commands in a safe environment before relying on them in production workflows (Love, 2013).

References

  • Kernighan, B. W., & Pike, P. J. (1984). The Unix Programming Environment. Prentice Hall.
  • Shotts, W. E. (2012). The Linux Command Line: A Complete Introduction. No Starch Press.
  • Nemeth, E., Snyder, G., Hein, T., & Whaley, B. (2017). UNIX and Linux System Administration Handbook (5th ed.). Pearson.
  • Sobell, M. (2010). A Practical Guide to UNIX for Mac OS X and Linux. Prentice Hall.
  • Kerrisk, M. (2010). The Linux Programming Interface. No Starch Press.
  • Love, R. (2013). Linux System Programming. O'Reilly Media.
  • Newham, C., & Robbins, A. (2003). Learning the Bash Shell. O'Reilly Media.
  • Patterson, S., Peek, J., & Robbins, A. (1996). Unix Power Tools. O'Reilly Media.
  • GNU Project. (2023). Core Utilities - find, head, ps, grep, wc. Retrieved from https://www.gnu.org/software/coreutils/
  • IEEE/ANSI. (2017). POSIX.1-2017 (IEEE Std 1003.1-2017). IEEE.

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