Linux/Unix Operating Systems Commands and Shell Scripting

In vi/vim, line ranges are specified using a comma separator, so :1,10s/NAME/name/ correctly substitutes the string on lines 1 through 10. Using % affects the entire file, omitting the range affects only the current line, and :1-10s is invalid syntax.

In Unix/Linux shells, the special variable $? holds the exit status/return code of the most recently executed command. A value of 0 typically indicates success, while non-zero values indicate various error conditions. The other options are different special variables.

The chown command (change owner) is the Unix/Linux utility used to change file ownership. 'chmod' changes permissions, not ownership. Options A and B are not valid commands for changing ownership.

The OR operator || runs the next command only if the previous failed. 'echo this' succeeds, so 'echo that' is skipped. The AND operator && runs the next command only if the previous succeeded, so 'echo other' executes. Output is 'this other'. The commands execute in sequence: this → (that skipped) → other.

The 'test' command (or [) uses = for string equality comparison in shell scripting. Options A and B incorrectly use -eq which is for numeric comparisons. Option C uses -equal which is not valid test syntax. Option D correctly uses = for string comparison.

The $! special variable in Unix/Linux shells contains the process ID (PID) of the most recently backgrounded command. When you run 'sleep 1 &', it starts in the background, and $! captures its PID. $$ is the current shell's PID, $? is exit status, $# is argument count.

The ln -s command creates symbolic (soft) links in Unix/Linux systems. The -s flag specifies a symbolic link rather than a hard link. Option A is the wrong command, option B creates hard links by default, and option D is not a valid command.

The find command is used to search directories recursively. The -name option specifies the filename pattern to search for, making find . -name file1 correct. ls commands list files but do not perform recursive file-matching searches, and find . -s is invalid syntax for this purpose.

In shell scripting, $# expands to the number of positional parameters passed to the script. Meanwhile, $? holds the exit status of the last executed command, $! contains the process ID of the most recent background command, and $$ represents the current shell's process ID.

The parameter expansion ${var} evaluates to the value of var, which is hello. The trailing x in echo ${var}x is treated as a literal character, resulting in the output hellox. Note that since the braces isolate var, it does not reference the variable varx.

The cmp utility compares two files byte-by-byte. The -s option runs it silently, returning an exit status of 0 if the files are identical, and 1 if they differ. Other options like -diff are invalid, and a non-zero or 1 exit status indicates differences or errors.

The nohup command prevents processes from receiving the SIGHUP signal when the user logs out, allowing them to continue running. This is its primary purpose - making commands immune to hangups when the shell session ends. The statement accurately describes nohup's functionality.

In Unix-like operating systems, the init process is the first process started during booting and is always assigned PID 1. PID 0 is typically the scheduler or idle process, PID 2 is reserved for kthreadd, and PID 100 is just a normal user-space process ID.

The cp -p command preserves file attributes including timestamps (atime and mtime), ownership, and mode. Regular cp copies content only. cp -r/-R are for recursive directory copies, and cp -i prompts before overwriting.

Ctrl+Z suspends a running process, then 'bg' resumes it in background. Ctrl+C terminates the process. 'fg' brings a background job to foreground, not background. Option A's order is wrong.

find's -mtime 2 finds files modified approximately 2*24=48 hours ago. The n in -mtime n means n 24-hour periods. -mtime 0 is less than 24 hours, -mtime 1 is 1-2 days, -mtime 2 is 2-3 days ago.

An inode is a Unix data structure that stores file metadata (permissions, ownership, size, timestamps, block pointers). Each file has a unique inode number. Kernel, shell, and 'filter' are not file identification structures.

The tee command reads from stdin and writes to both stdout and a file. echo 'hello world' | tee temp.txt displays on screen AND saves to temp.txt. Single > only redirects to file, no display.

ls -l lists files in long format where first character indicates type: 'd' for directory, '-' for regular file. grep ^d filters lines starting with 'd'. Option C misses -l, and grep dir would search for 'dir' in filenames.

head -10 file displays the first 10 lines. tail -10 shows the last 10. cat displays entire file. head +10 is not valid syntax (that's how tail works).