Commands

Encyclopedia4U defines the term commands, in computing, as computer programs invoked from console environment (command line interface). Wikipedia, on the other hand, defines command as a directive to a computer program acting as an interpreter of some kind, in order to perform a specific task. Put simply, a command is a statement in a computer language. A command acts as a signal for the system to start or initiate an operation based on the user's instruction. Wikipedia adds that a command is most commonly a directive to some kind of command line interface, such as a shell.

Generally, users of MS-DOS, Unix, Linux and other operating systems utilize commands to perform various tasks such as creating directories or files, processing text, and viewing and editing files. There are many different commands that have to be entered at the shell prompt or command prompt to work with these operating systems.

For example, widely used Unix commands for text processing include:
echo
cat
grep
sort
uniq
sed
awk
cut
tr
split
printf

The cat command is used to create, view and concatenate files; the grep command is used to search for information in a file or files; and the sort command is for sorting a file.