# Notes on bash (and linux)

## If you forget where you are:

```bash
hostname
```

## For disk usage analysis:

```bash
sudo du -sh ./*
df -h
```

## Count the number of files in a directory.

```bash
find . -type f | wc -l
```
## Recursively find all files with a given extension

(I can never remember `find` syntax.)

```bash
find . -name *.rabl
```

## Sum the numbers in the first | delimited column in list.txt

```bash
cut list.txt -d'|' -f1 | awk '{s+=$1} END {print s}'
```

## Rename extensions

```bash
for i in *.php; do mv "$i" "${i/.php}".html; done
```

## Ubuntu stores its mail

```bash
var/mail/username
```

## Show what distro you're using:

```bash
lsb_release -a
```

## Show the latest exit code. 1 is true, 0 is false

```bash
echo $?
```

## Bash shells and config files.

```
A login shell is when you get the little introductory text like when using ssh. Opening up a console via gnome-terminal locally is not a login shell
Pretty much everything is treated as an interactive shell, even scp.
"When bash is invoked as an interactive login shell ... it first reads and executes commands from the file /etc/profile, if that file exists. After reading that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads and executes commands from the first one that exists and is readable."
"When an interactive shell that is not a login shell is started, bash reads and executes commands from /etc/bash.bashrc and  ~/.bashrc, if these files  exist."
```

## To set up ssh bash_completion

```bash
/etc/bash_completion.d/ssh
```

## Run something so that logging out won't kill it

```bash
nohup bundle exec rake db:set_unit_names >> log/unit_names.log 2>&1 &
```

## Remove Old Kernels

```bash
ls /boot/ | grep vmlinuz | sed 's@vmlinuz-@linux-image-@g' | grep -v `uname -r`
sudo aptitude remove $old_kernel
```

## Redirect a single page to ssl in a vhosts file 

```bash
Redirect /payments https://www.mokisystems.com/payments
```

## tar and gzip

```bash
tar -czf filename.tar.gz directory # Create
tar -xzf filename.tar.gz # Extract
```

## Renew dhcp lease

```bash
sudo dhclient -r && sudo dhclient
```

## Set up a new server

```bash
vim ~/.ssh/config
SERVER=new_server
ssh $SERVER
adduser daniel
vim /etc/group # add to moki group
visudo # add to sudoers file ^K^U^U ^X
exit
ssh-copy-id $SERVER #make sure /home/daniel is not group writable.
sync_server_dotfiles $SERVER
```

## Edit iptables

```bash
sudo vim /etc/iptables.rules
sudo iptables-restore < /etc/iptables.rules
```

## Grep installed packages

```bash
dpkg --get-selections | grep pattern
```

## Password protect a file

```bash
gpg -c db.sql.gz # encrypt
gpg -d db.sql.gz.gpg > db.sql.gz # decrypt
```

## Restart delayed jobs based on current directory

```sh
function rsdj {
  if [ $(basename `pwd`) == 'devstorage' ]; then
    sudo monit delayed_job_staging restart
  elif [ $(basename `pwd`) == 'storageunitsoftware' ]; then
    sudo monit -g delayed_job_production restart
  else
    echo 'delayed_jobs restart: Production or staging?'
  fi
}
```

## Start `less` without control characters and line numbers 

```sh
less --RAW-CONTROL-CHARS --line-numbers
```

## Debug running a program

```sh
export LD_DEBUG=files # or bindings, libs, versions
program_to_debug
```

## Get Public Key from Private

```sh
ssh-keygen -yf private_key_file > public_key_file
```

## Show fingerprint of public key file

```sh
ssh-keygen -lf public_key_file
```

## Connect to Redis

```sh
nc -v redis.endpoint.com 6379
ping
```