Unix/Linux Shell Scripting and System Administration

In vi editor, 'db' deletes the previous word (word before the cursor). The 'd' command is for delete, and 'b' stands for 'back' or previous word. 'dW' would delete a WORD (space-separated), 'dd' deletes entire line, and 'dG' deletes to end of file.

Vi editor has three main modes: command mode (default, for navigation and commands), insert/input mode (for typing text), and last line mode (also called ex mode, entered with : for complex commands). All three modes listed are valid vi editor modes.

IPQoS (IP Quality of Service) enables policy-based bandwidth provisioning for both inbound and outbound network traffic. It does not automatically configure IP interfaces, nor does it limit prioritization to only one direction of traffic.

Before initializing NIS services, you must first update or create the ASCII source files that contain the data to be distributed. Commands like nisinit and ypinit are run after the source files are prepared.

The ntpdate command is used to synchronize the local system clock with a remote NTP server. ntpsync and ntpscan are not standard commands, and ntpd.conf is a configuration file not a command.

netfmt is the HP-UX command used to format binary trace data generated by nettl (the network tracing/logging tool). nroff is a text formatter, and the other options are not valid commands for this purpose.

On HP-UX, when cron.deny exists but is empty and cron.allow does not exist, all users can use cron. The deny file takes precedence, but since it's empty, no users are blocked. If only cron.allow existed, only listed users could use cron.

To re-execute command 143 (pwd), valid methods are: r 143 (re-run by number), r -8 (re-run 8 commands back), and fc -s 143 (fix and run). The command 'fc -e -r p' (B) is syntactically problematic - 'fc -e' expects an editor name, and the flag combination doesn't constitute a valid re-execution method. This makes B the correct answer to 'which is NOT a valid method.'

The fmt command in Unix/Linux is specifically designed for text formatting operations including margin justification, crown margin mode, and line wrapping. nroff is document formatting, mm is a macro package for groff, and tbl is table formatting - none handle crown margin mode directly.

This script checks if $l is prime by testing divisibility from 2 upward. If $l % i == 0 (divisible), it prints and breaks with exit status 0 (success). If no divisor found, loop completes naturally, exit status is 1 (failure) from the last comparison. The 'print' statement only executes when not prime (divisor found), so output appears when not prime; no output when prime.

The beach.sh script iterates over words in $1. ${#i} gives string length. Words longer than 4 characters get prefixed with '#'. From 'On the beach at night, stands a child with her father': 'beach'(5), 'night,'(6), 'stands'(6), 'child'(5), 'father'(6) qualify. Punctuation like comma in 'night,' counts as part of the word.

In Unix shells like KornShell (ksh), the let command is used for arithmetic evaluation. let x=32+8 evaluates the expression and assigns the integer value 40 to the variable x.

The fc command lists command history. 'fc -l -50' shows the last 50 commands (negative number counts back from most recent). 'fc -l 50' would start from command 50. 'history 50' shows the last 50 commands but with different format. 'history $$' is nonsensical ($$ is current PID).

In shell globbing with extended patterns, ?([aA]*) matches zero or one occurrences of a string starting with 'a' or 'A' followed by any characters, which effectively matches the null string or filenames beginning with 'a' or 'A'.

By default, echo * expands the glob * to list all files in the current directory. 'set -f' (or 'set -o noglob') disables glob expansion, causing * to be treated literally. 'set -t', 'set -m', and 'set -l' control other shell options and don't affect globbing.

A backslash () at the end of a line acts as a line continuation character, allowing a command to span multiple lines. Single quotes start/end a quoted string, front slash is path separator, and full stop ends a sentence or denotes current directory.

This is a duplicate of question 136528. By default, echo * expands the glob * to list all files. 'set -f' disables glob expansion, causing * to be treated literally. The other options control different shell features.

This is a duplicate of question 136524. The script iterates over words and prefixes those longer than 4 characters with '#'. Words qualifying: 'beach'(5), 'night,'(6), 'stands'(6), 'child'(5), 'father'(6). Punctuation is included in character count.