MOVING AROUND
ls, cd and pwd
The GNU manual calls ls the program that lists directory contents, and pwd prints the working directory. The POSIX standard says cd changes the working directory.
Check a commandWHAT THE MANUALS SAY
Every command
is a short word.
The command line has its own vocabulary.
Most of it is shorthand: ls for list, pwd for print working directory, grep for an old editor command. Once you can read the words, you can tell which ones only look and which ones change things.
Check a command Read the short answer
01 Know what it stands for02 Know what it changes03 Ask the manualShort words, clear meanings
THE SHORT ANSWER
Most commands are
abbreviations.
The names look cryptic, but most are shorthand.
Read the word and you know the job.
SEARCHING
Where grep comes from
The GNU grep manual says the name comes from the old ed editor, where g/re/p meant global, regular expression, print: show every matching line.
See the history
POWER
sudo means su “do”
The sudo project describes it as su “do”: it lets an administrator give chosen users the power to run commands as root, with a record of what was run.
Use it carefullyA QUICK COMMAND CHECK
What does this
command change?
Pick a common command to see what its name means and how much it can change on your computer. The bar shows how much care it deserves before you press Enter.
Based on the GNU Coreutils manual and the sudo project's own description. General information, not advice for any particular system.
TWO NUMBERS WORTH KNOWING
The manual is old,
and well organised.
One figure on how the manual is divided,
one on how long sudo has been around.
THE MANUAL
Numbered sections in the man pages
9 sections
The man command's own page lists sections 1 to 9: 1 is for programs and shell commands, 8 for system administration commands, usually only for root, and 9 (non-standard) for kernel routines.
SUDO
When sudo was first written
≈ 1980
The sudo project says sudo was first conceived and implemented around 1980 at the Department of Computer Science at SUNY/Buffalo. An updated version was posted to Usenet in December 1985.
Sources: man(1) on man7.org; A Brief History of Sudo on sudo.ws.
SAFER HABITS
Read the words,
then press Enter.
A few habits taken straight from the manuals make the command line less risky.
- Check where you areRun pwd before a command that changes files, so you know which directory it will act on.
- Look before you changeUse ls to see what is there. It only lists, so it is safe to run as often as you like.
- Ask to be askedAdd -i to mv or rm and they will ask before overwriting or removing each file.
- Keep sudo for when you need itsudo runs a command as root, the most powerful user. Use it only for the commands that truly need it.
THE MANUAL
When in doubt,
type man.
Almost every command has a manual page. Typing man ls shows the page for ls, and man looks through the numbered sections in order and shows the first page it finds.
Section 1 covers programs and shell commands, section 5 file formats such as /etc/passwd, and section 8 system administration commands, which are usually only for root.
QUESTIONS PEOPLE ASK
Frequently asked
What does ls stand for?
It is short for list. The GNU Coreutils manual describes ls as the program that lists information about files, including directories. By default it skips names that begin with a dot.
Why is it called grep?
The GNU grep manual says the name comes from the way line editing was done on Unix: in the ed editor, g/re/p meant global, regular expression, print, which shows every matching line.
What does sudo mean?
The sudo project describes it as su “do”. It lets a system administrator allow chosen users to run some or all commands as root or another user, and keeps an audit trail of the commands run.
Is cd a program like ls?
No. cd changes the working directory of the current shell, and the POSIX standard says that because of this it is always provided as a shell built-in rather than a separate program.
Can rm ask before deleting?
Yes. The GNU manual says rm -i prompts before removing each file, and rm -I prompts once if more than three files are named or a recursive removal is requested.
SOURCES
Where the facts come from
Each figure on this page comes from the sources below. Check them for the full detail and context.