Unix/Linux Operating System Commands

When running a script with 'sh test.sh', the shell reads the entire file into memory before executing it. This means the script can safely delete itself during execution without affecting its ability to complete. Both echo statements will execute successfully, and the file will be removed.

A filename beginning with a hyphen must be separated from option parsing. Using rm -f -- -p tells rm that everything after -- is a filename, reliably deleting the file. The other forms either treat -p as an option or misuse quoting.

The Unix date command accepts both numeric format (MMDDhhmm) and string format with the -s flag. Option 'a' provides the numeric representation where 1123180809 means November 23, 18:08, and option 'c' provides the full date string format. Both methods successfully change the system date.

To send a running foreground process to the background, first suspend it with Ctrl-Z (stops it and returns control to the shell), then use 'bg' to resume it in background mode. The job continues running but no longer occupies the terminal or requires user interaction.

The uuencode command converts binary files to ASCII format, allowing them to be sent as email attachments through the mailx utility. When piped to mailx, it properly formats the file as an attachment rather than inline text, which is the traditional Unix method for email attachments.

The condition [ $i -lt 2 ] evaluates to false since 2 is not less than 2. In bash, the || operator executes the right side only if the left side returns false (exit code non-zero). Therefore, 'echo great' runs and outputs 'great' to the terminal.

When a script runs with 'sh test.sh', it executes in a separate shell process. Exported variables only affect child processes of that script, not the parent shell. After the script exits, the variable i no longer exists in the current shell, resulting in an empty line when echoed.

cd - switches the shell back to the directory stored in OLDPWD and prints that path. It does not always go to the home directory; it specifically uses the previously saved location, making the selected option correct.

The TZ environment variable stores the system's timezone setting, which affects how time-related commands display and calculate time. Echoing $TZ shows the current timezone value, such as 'America/New_York' or 'IST', which is used by various system utilities.

Grep's exit status reflects pattern matching results - returning 0 when matches are found and 1 when no matches exist - making it ideal for script decision-making based on $? Awk always returns exit code 0 regardless of match outcomes, so it cannot signal match/non-match conditions through the exit status variable.

The 'lsvg -o' command on AIX lists only active (varied on) volume groups. The plain 'lsvg' shows all volume groups regardless of state, while '-o' filters for only those that are currently online and active. The 'lsvg -a' option is invalid, and 'activevg' is not a standard AIX command.

The echo command simply prints the literal string to stdout without any evaluation. Since '32' is enclosed in quotes, echo outputs exactly '32' as text, not the mathematical result 6. Arithmetic evaluation would require $((3*2)) or expr in shell.

The dot command '.' or 'source' executes a script in the current shell environment rather than spawning a new subshell. This allows the script to modify the current shell's variables and environment. './test.sh' runs in a subshell, 'sh test.sh' spawns a new shell, and 'exec' replaces the current shell process.