System Commands · Quiz 1 · Jan 2026

**1. Follow the hard links:** touch creates project.doc with one inode. project_copy and project_backup are hard links to that same inode. **2. Count the symbolic link:** project_link is a separate symbolic-link object with its own inode. Thus the four names represent two newly allocated inodes. **Answer: 2.** **Convention note:** This counts the objects created by the commands, excluding already existing directory and filesystem inodes.

**1. Decode the three permission fields:** report.txt is rw-r--r--; compile.sh is rwxr-----; readme.md is r--r--r--. **2. Apply the relevant category:** The report owner has write permission; dev has read permission on the report. Neither group nor others has execute permission on compile.sh. Every category has read permission on readme.md. **Answer: A, D, E — A, D and E.** **Convention note:** Permission statements use the normal owner/group/others model and assume the necessary directory access. The owner’s rights are evaluated as owner, not as a group member. A: **Correct:** The owner field of report.txt includes w. B: **Incorrect:** The others field of compile.sh is ---, so ordinary nonowners outside dev cannot execute it. C: **Incorrect:** The dev group field is r--, without x. D: **Correct:** The group field of report.txt contains r. E: **Correct:** Owner, group and others all have r.

**1. Compare default regex syntax:** egrep is the ERE form of grep -E. In ERE, |, + and ? have their special meanings without backslashes; plain grep uses BRE, where these unescaped symbols do not have those meanings. **2. Select the syntax statements:** A and B describe the unescaped syntax difference, and D gives the equivalent invocation. C incorrectly claims identical syntax; E reverses the modes. **Answer: A, B, D — A, B and D.** **Convention note:** GNU BRE also supports escaped \|, \+ and \? as extensions. Thus “grep does not” in A/B refers to the unescaped operator forms, not a complete lack of equivalent functionality. A: **Correct:** Unescaped | supplies alternation in ERE, unlike BRE. B: **Correct:** Unescaped + and ? are ERE repetition operators, unlike their unescaped BRE forms. C: **Incorrect:** The default syntaxes differ. D: **Correct:** egrep conventionally invokes the grep -E mode. E: **Incorrect:** Plain grep defaults to BRE and egrep to ERE.

**1. Enforce both boundaries:** ^report requires the lowercase prefix at the beginning; \.txt$ requires the literal extension at the end. **2. Compare the middle:** A permits any characters with .*; C permits non-slash characters with [^/]*. No supplied line contains a slash, so these produce the same desired lines. **Answer: A, C — Commands A and C.** A: **Correct:** It enforces the exact prefix and suffix while allowing intermediate characters. B: **Incorrect:** -w is not an end-of-line anchor; report.txt.bak can still match the report.txt word. C: **Correct:** On the given slash-free lines it matches exactly the same desired filenames as A. D: **Incorrect:** It matches only report.txt, omitting report1.txt and other valid extensions of the prefix.

**1. Specify the character positions:** After file_, [a-z] requires one lowercase letter and [0-9] requires one digit; .txt is a literal glob suffix. **2. Count the matching names:** file_a1.txt and file_b2.txt match. ls writes them to the pipe one per line under ordinary output settings, and wc -l counts those lines. **Answer: C — ls file_[a-z][0-9].txt | wc -l.** **Convention note:** The question’s intended prefix includes the underscore shown in the filenames. This familiar ls-count pipeline assumes ordinary filenames and at least one match. A: **Incorrect:** ?? accepts any two characters, including the wrong order or two letters. B: **Incorrect:** Each class permits letters or digits, so it is too broad. C: **Correct:** It imposes the requested letter-then-digit order. D: **Incorrect:** It requires digit-then-letter, the opposite order.

**1. Prove possession:** During public-key authentication the client signs authentication data using its private key. The server verifies the signature using the authorized public key; the private key stays on the client. **Answer: C — It is used by the client to prove its identity to the server without sending the .** A: **Incorrect:** The private key itself is not sent to the server. B: **Incorrect:** Session encryption normally uses separately negotiated symmetric keys. C: **Correct:** A signature proves possession without disclosing the private key. D: **Incorrect:** Server fingerprints are recorded separately, typically in known_hosts.

**1. Match Vim:** :q! quits without saving (D); :set number displays line numbers (C); :x saves if modified and quits (B); :! runs an external command (A). **2. Match Emacs:** M-< moves to buffer beginning (D); C-a to line beginning (C); M-> to buffer end (B); C-e to line end (A). Both tables therefore use 1-D,2-C,3-B,4-A. **Answer: B — 1-D, 2-C, 3-B, 4-A for both tables.** A: **Incorrect:** It swaps the third and fourth functions. B: **Correct:** This mapping agrees with both editor tables. C: **Incorrect:** It misassigns quit/save functions. D: **Incorrect:** It misassigns quit and terminal-command functions.

**1. Redirect stdout:** > output.txt creates or truncates the normal-output file. **2. Redirect stderr:** 2>> errors.txt appends descriptor 2 while preserving previous error content. Combining the two gives option A. **Answer: A — ./run_test.sh > output.txt 2>> errors.txt.** A: **Correct:** It truncates stdout’s file and appends stderr’s file. B: **Incorrect:** It reverses append and overwrite behaviour. C: **Incorrect:** &>> combines both streams into output.txt; errors.txt is then an argument. D: **Incorrect:** It sends the two streams to the opposite requested files.

**1. Gate deployment on success:** && runs the deployment pipeline only when ./build.sh succeeds. **2. Filter deployment output:** The pipeline ./deploy.sh | grep "SUCCESS" > deploy.log saves just the matching deployment lines. This is the structure in A. **Answer: A — ./build.sh && ./deploy.sh | grep "SUCCESS" > deploy.log.** **Convention note:** This saves matching lines but does not simultaneously show them on the terminal. If “display” literally requires both destinations, use grep -w "SUCCESS" | tee deploy.log; -w also enforces the whole word. A is the intended offered pipeline. A: **Correct:** It gates the deployment pipeline on build success and saves its filtered output. B: **Incorrect:** It filters build output and saves unfiltered deployment output. C: **Incorrect:** The deployment stdout redirection bypasses grep’s input. D: **Incorrect:** || starts deployment after build failure instead of success.

**1. Parse the anchored pattern:** ^[a-z0-9._]+ allows one or more lowercase letters, digits, dots or underscores before @; [a-z]+ requires lowercase letters in the next component. **2. Parse the ending:** \. is a literal dot and [a-z]{2,4}$ requires a two-to-four-letter final component at the end. The whole line must match this simplified email form. **Answer: B — Complete simplified lowercase email form with a 2–4 letter suffix.** **Convention note:** The 2–4 length restriction applies to the final suffix, not the full domain name. The regex is a classroom pattern rather than a complete email-address validator. A: **Incorrect:** The anchors prohibit arbitrary extra text, and digits and punctuation are allowed in the local part. B: **Correct:** It describes the complete anchored lowercase email-like form. C: **Incorrect:** The local part may start with a digit, dot or underscore too. D: **Incorrect:** The pattern constrains the entire line rather than any @ and dot occurrence.

**1. Match each tool:** ping sends reachability probes (C); traceroute discovers a hop-by-hop route (D); nslookup queries DNS (A); netstat reports network connections and related statistics (B). **Answer: C — 1-C, 2-D, 3-A, 4-B.** A: **Incorrect:** Every mapping is shifted away from the tool’s function. B: **Incorrect:** The functions are reversed. C: **Correct:** All four command-purpose mappings are correct. D: **Incorrect:** It swaps the DNS and route-discovery functions.

**1. Apply AND-list semantics:** cmd1 && cmd2 executes cmd2 after a zero exit status from cmd1. **2. Apply OR-list semantics:** cmd1 || cmd2 executes cmd2 after a nonzero exit status from cmd1. Therefore both statements are true. **Answer: C — Both statements are true.** A: **Incorrect:** Statement II is also true. B: **Incorrect:** Statement I is also true. C: **Correct:** Both are the shell’s short-circuit rules. D: **Incorrect:** Both stated rules are correct.

**1. Isolate the prefix:** head -11 produces lines 1 through 11. **2. Keep the requested seven lines:** There are \(11-5+1=7\) lines from 5 to 11; tail -7 on the prefix yields exactly them. **Answer: D — cat longfile.txt | head -11 | tail -7.** A: **Incorrect:** It keeps only lines 1–4. B: **Incorrect:** It takes four lines from the file’s last eleven. C: **Incorrect:** It takes the last seven lines of the entire file. D: **Correct:** It takes the final seven lines of the first eleven.

**1. Expand the alternatives:** [1-9] covers 1–9, [1-9][0-9] covers 10–99, 1[0-1][0-9] covers 100–119, and 12[0-6] covers 120–126. **2. Apply the boundaries:** ^ anchors the first octet and \. ends it. Thus first octets 1–126 match, while 127 and all Class B octets do not. **Answer: A — Only the stated Class A range, excluding loopback.** A: **Correct:** The alternatives cover precisely the stated Class A range. B: **Incorrect:** 127 is excluded by the final digit range 0–6. C: **Incorrect:** Class B starts at 128 and is excluded. D: **Incorrect:** No first octet 128–191 matches.

**1. Create the new directory and file:** Docs exists, so mkdir Docs/Guides succeeds. touch Docs/Guides/linux.md places the empty file correctly. **2. Generate the reports:** B uses report{2..10}.txt; D explicitly lists report2 through report10 inside braces. Both create the nine requested files in Work/Reports. **Answer: B, D — Command sets B and D.** A: **Incorrect:** After cd Docs it creates linux.md in Docs, not Docs/Guides. B: **Correct:** It creates the correct directory, file and expanded report names. C: **Incorrect:** It swaps the file and directory roles and does not expand the report range. D: **Correct:** Its explicit brace list expands to the nine requested report filenames.

**1. Move the original:** mv Work/Reports/report1.txt Backup/ removes its old directory entry and places the file in Backup. Reports is now empty in this independent scenario. **2. Remove and list:** A removes the empty directory with rmdir; B removes it with rm -rf. Both then list Backup. **Answer: A, B — Command sets A and B.** A: **Correct:** It moves the file, removes the now-empty directory and lists the destination. B: **Correct:** It achieves the same result using recursive removal on the now-empty directory. C: **Incorrect:** cp leaves the original in Reports, so rmdir fails. D: **Incorrect:** Plain rm refuses a directory without an appropriate directory/recursive option.