Basic Unix Commands Quiz

chmod -R a+x progs makes all files and subdirectories (-R for recursive) executable for all users (a+x = all users + execute). chmod -R 222 would give write-only, not execute. chmod -1 is invalid syntax (should be -R). The command in A is the correct way to recursively set execute permissions.

The touch -a command in Unix/Linux is specifically used to change the access time of a file. The -m flag changes the modification time, and -t allows for a specific timestamp.

The cp command copies files by taking source and destination file paths as command-line arguments, not from standard input. It writes data directly to the destination file, not to standard output. This distinguishes cp from commands like cat or tr that read from stdin or write to stdout.

The sort command's +m.n option skips the first m fields, then skips n additional characters in the next field before sorting. This allows sorting to begin at a specific position within fields, ignoring leading characters or fields. The -k option (GNU sort extension) provides more flexible field specification.

The file command examines file contents and determines the file type by analyzing its magic numbers, structure, and content patterns. Unlike ls which only shows metadata, file actually inspects the file's internal characteristics to identify whether it's a text file, executable, image, archive, etc.