Files and directories

vim

vim.nox is a minimal flavor of vim for server environments that has scripting language support.

command mode lets you move around the file
insert mode lets you edit text
visual mode lets you select text for copy/paste
Add default settings to .vimrc in /home dir. Ex: set number

CTRL + z        # put vim session in background
fg              # bring vim session to foreground
A               # insert mode at the end of the current line
gg              # go to beginning of first line of file
G               # go to beginning of last line of file
:%s/original string/new string/g    # global replace
:! <shell command>                  # run <shell command> while vim is open
:set number     # add line numbers
:set nonumber   # remove line numbers

# --- Split files --- #
:sp /path/to/file                   # split current window with file window
:vs /path/to/file                   # vertical split window and file
CTRL + w, CTRL + w                  # switch between open files

Streams

STDIN, STDOUT, STDERR

Every program is a process, and every process has 3 distinct file descriptors:

stdin: File descriptor 0. Default source for input to a program
stdout: File descriptor 1. Default place for sending output (the console)
stderr: File descriptor 2. Where error messages are written

Redirection and piping

Redirection is when you change the input and outputs of a program without modifying the program.

Operator	Description	Example
`>`	Sends the output of the value on the left to the value on the right.	`ls -la > listing.out`
`<`	Sends the value on the right to the STDIN of the value on the left.	`program < input.txt`
`2>`	Redirect STDERR messages to the value on the right.	`cp -r /etc/a /etc/b 2> err.msg`
`2>&1`, `&>`	Send output to STDOUT and STDERR. Place this	`XXXXXXXXXXX`
`1> file 2>`	Redirect more than one stream	`find / -name 'syslog' > stdout.txt 2> stderr.txt`

The following command sends input.txt to the STDIN of program, and sends the output to output.out:

program < input.txt > output.out

To distinguish between STDOUT and STDERR, use the file descriptor 2>. The following command redirects error messages to err.msgs:

program 2> err.msgs

Or, combine all redirection methods:

program < input.txt > output.out 2> err.msgs

Combined redirect: To send STDERR to the same location as STDOUT, combine the error messages with the standard output:

program < input.txt > output.out 2>&1
# shorthand
program < input.txt &> output.out

The previous command sends input.txt to program, then sends the STDOUT and STDERR to output.out. The shorthand is more clear.

Commonly, you can discard STDOUT by sending it to /dev/null:

program < input.txt > /dev/null

The tee command sends output to STDOUT and the file that follows the command:

program < input.txt | tee results.out # the -a option allows tee to append to the file

To append to a file, use the >> operator:

program < input.txt >> appended.file

To append STDOUT and STDERR, use &>>:

program < input.txt &>> appended.file

Running commands in the background

Use the & operator at the end of the command to run it in the background:

ping 10.20.30.40 > ping.log &

When you run a task in the background, send both STDOUT and STDERR so the task doesn’t log everything to the console:

ping 10.20.30.40 &> ping.log &

To bring a job back to the foreground, use jobs to list running tasks, then use fg with the corresponding task number:

ping 192.168.10.56 &> ping.log &
[1] 7452
jobs
[1]+  Running                 ping 192.168.10.56 &> ping.log &
fg 1
ping 192.168.10.56 &> ping.log
^C

Stop a running job with Ctrl+z, and send it to the background with bg:

ping 192.168.10.56 &> ping.log &
[1] 7572
fg 1
ping 192.168.10.56 &> ping.log
^Z
[1]+  Stopped                 ping 192.168.10.56 &> ping.log
bg 1
[1]+ ping 192.168.10.56 &> ping.log &
fg 1
ping 192.168.10.56 &> ping.log
^C

Files and directories

vim

Streams

STDIN, STDOUT, STDERR

Redirection and piping

Running commands in the background

Links

Hard link

Symbolic link