BASH COMMANDS starts - R,S,T,U

R

ram: Ram disk device
rcp: When using two machines, this command copies files between them.
read: This commands is used for reading a line from standard input.
readarray: This commands reads from stdin into an array variable.
readonly: This command marks the variables and functions as readonly.
reboot: Self explanatory, use this command to reboot your system.
rename: Rename files
renice: This command alters the priority of the processes running.
remsync: This command synchronises remote files through email.
return: This is used to exit from a shell function.
rev: This command reverses the lines in a file.
rm: Use this to remove particular files.
rmdir: Same as above, but for directories.
rsync: This is for synchronising file trees.

S

screen: Use this to run remote shells using ssh.
scp: This is used to create a secure copy.
sdiff: This command is used to merge two files in a secure manner.
sed: This is for the stream editor.
select: This is used when you need to accept keyboard inputs.
seq: This command is used for printing numeric sequences.
set: This command lets you manipulate shell functions and variables.
sftp: Run the secure file transfer program using this.
shift: This command is used for shifting positional parameters.
shopt: Shopt stands for Shell Options.
shutdown: Use this command when you want to shutdown Linux or restart it.
sleep: Add a delay using this command.
slocate: This is used to find particular files.
sort: Text files are sorted using this.
source: This command is used for running commands from a file.
split: This command is used to break a file into fixed sizes.
ssh: This is used to run the remote login program, that is, the secure shell client.
strace: This is used to trace signals and system calls.
su: Substitute the user identity using this command.
sudo: This is used for executing commands as a different user.
sum: File cheksums are printed using this command.
suspend: This command is used to suspend the execution of the current shell.
sync: This command is used in order to synchronise data from a disk with the memory.

T
tail: Use this command when you want to output only the last part of a file.
tar: This command is used in order to store a list or extract files in an archive.
tee: This command is used for redirecting output into multiple files.
test: This command is used for evaluating conditional expressions.
time: The running time of a program can be measured using this command.
timeout: This command is used to put a time limit on a command.
times: Use this to find the user and system times.
touch: Timestamps on a file can be changed using this.
top: This is used to get a list of the processes that are running on the system.
traceroute: Use this command to Trace Route to a host.
tr: Delete characters, translate or squeeze them.
tsort: This is used for topological sorting.
tty: This is used for printing the filename of terminal on stdin.

U

ulimit: This commands limits the user resources.
umask: This is used to determine the file permission for a new file.
umount: This command will unmount a device from the system.
unalias: This command will remove an alias.
uname: This command will print the system information.
unexpand: This command will convert the spaces in a file to tabs.
uniq: This command will uniquify your files.
units: This will convert the units from one scale to another.
unset: This command removes the variable names or the function names.
unshar: This command unpacks the shell archive scripts.
until: This command will execute a command until there is an error.
uptime: This command will show the uptime.
useradd: Use this command when you need a new user account to be created.
userdel: This command will delete an user account from your system.
usermod: Self explanatory, modify an user account.
users: This command gives you a list of users who are currently logged in.
uuencode: This command will encode binary files.