some linux commands in alphabetic order

A
alias - create names or abbreviations for commands
apropos - search the manual page names and descriptions
at [man page] - queue, examine or delete jobs for later execution

B
bc [man page] - An arbitrary precision calculator language

C
cal - displays a calendar
cat [man page] - concatenate files and print on the standard output
cd - change directory
chgrp [man page] - change group ownership
chmod [man page] - change file access permissions
cksum [man page] - checksum and count the bytes in a file
cp [man page] - copy files and directories
csplit [man page] - split a file into sections determined by context lines

D
date [man page] - print or set the system date and time
dd [man page] - convert and copy a file
du [man page] - estimate file space usage

E
egrep [man page] - print lines matching a pattern
export - set an environment variable

F
fgrep [man page] - print lines matching a pattern
find [man page] - search for files in a directory hierarchy
fold [man page] - wrap each input line to fit in specified width

G
grep [man page] - print lines matching a pattern

H
head [man page] - output the first part of files

I

J
join [man page] - join lines of two files on a common field

K

L
logrotate [man page] - rotates, compresses, and mails system logs
ls [man page] - list directory contents

M
mkdir [man page] - make directories
mv [man page] - move (rename) files
mount [man page] - mount a file system

N
nl [man page] - number lines of files

O
od [man page] - dump files in octal and other formats

P
pwd [man page] - print name of current/working directory

Q

R
rgrep [man page] - print lines matching a pattern
rm [man page] - remove files or directories

S
scp - secure copy (remote file copy program)
ssh - OpenSSH SSH client (remote login program)

T
tail [man page] - output the last part of files
tar [man page] - The GNU version of the tar archiving utility
tee [man page] - read from standard input and write to standard output and files
time [man page] - run programs and summarize system resource usage
touch [man page] - change file timestamps

V
vim - Vi IMproved, a programmers text editor

W
watch [man page] - execute a program periodically, showing output fullscreen
wc [man page] - print newline, word, and byte counts for each file
whoami [man page] - print effective userid

X

Y
yes [man page] - output a string repeatedly until killed

Z