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What does the AT command do?
at command is a command-line utility that is used to schedule a command to be executed at a particular time in the future. Jobs created with at command are executed only once. The at command can be used to execute any program or mail at any time in the future.
What is ls command in terminal?
The ls command writes to standard output the contents of each specified Directory or the name of each specified File, along with any other information you ask for with the flags. If you do not specify a File or Directory, the ls command displays the contents of the current directory.
What is option for ls?
ls command options
| option | description |
|---|---|
| ls -l | list with long format – show permissions |
| ls -la | list long format including hidden files |
| ls -lh | list long format with readable file size |
| ls -ls | list with long format with file size |
What are the options in the command line?
In the original Unix tradition, command-line options are single letters preceded by a single hyphen. Mode-flag options that do not take following arguments can be ganged together; thus, if -aand -bare mode options, -abor -bais also correct and enables both. The argument to an option, if any, follows it (optionally separated by whitespace).
How to distinguish command line options from ordinary arguments?
Three conventions for how to distinguish command-line options from ordinary arguments exist; the original Unix style, the GNU style, and the X toolkit style. In the original Unix tradition, command-line options are single letters preceded by a single hyphen.
How to use the for command at the command prompt?
Use a single percent sign ( %) to carry out the for command at the command prompt. Use double percent signs ( %%) to carry out the for command within a batch file. Variables are case sensitive, and they must be represented with an alphabetical value such as %a, %b, or %c.
Why are there single letter options in Unix?
The original Unix style evolved on slow ASR-33 teletypes that made terseness a virtue; thus the single-letter options. Holding down the shift key required actual effort; thus the preference for lower case, and the use of “-” (rather than the perhaps more logical “+”) to enable options.