====== Linux Programming ======
Usar la salida del último comando (volviendolo a ejecutar):
<code>
$ > echo pierre
pierre
$ > echo my name is $(!!)
echo my name is $(echo pierre)
my name is pierre
</code>
Exit status del último comando:
<code>
$ touch /root/test
touch: cannot touch '/root/test': Permission denied
$ echo $?
1
</code>
Añadir la salida de un comando como parámetro a otro
<code>
$ ls $(echo ~)
</code>
Guardarlo en una variable
<code>
alfred@alfred-Y50-70 ~/Desktop $ a=$(python crawler.py)
alfred@alfred-Y50-70 ~/Desktop $ echo $a
</code>

Run with root:
<code>
if [ "$(id -u)" != "0" ]; then
   echo "This script must be run as root" 1>&2
   exit 1
fi
</code>
Si quieres que el script pare cuando haya un error interno añade la siguiente línea al inicio de este:
<code>
set -e
</code>
===== Fast notes =====
=== Check if a directory or file exists ===
Looking the status code of:
<code>
test -d /path
</code>

=== Wait to press a key ===

<code>
read -n1 -r -p "Press any key to continue..." key;
</code>

=== Override a line in a config file ===
<code>
sed -i 's/# auth-access = write/auth-access = write/' src/conf/svnserve.conf
sed -i 's/# password-db = passwd/password-db = passwd/' doc/conf/svnserve.conf
</code>

=== Get formatted data ===
get year-month-day from date
<code>
DATE=`date +%Y-%m-%d`
</code>
get year-month-day hour:minute:second from date
<code>
DATE=`date '+%Y-%m-%d %H:%M:%S'`
</code>
<code>
$ DATE=$(date +%y%m%d)
$ echo $DATE
190523
</code>
===== Examples =====
Some Django shortcuts:
<code>
resetmigrations() {
  if [ -z "$1" ]
    then
      echo "No database supplied"
      return
  fi
  echo "The $1 database is going to be reseted";
  read -n1 -r -p "Press any key to continue..." key;
  find . -path "*/migrations/*.py" -not -name "__init__.py" -delete
  find . -path "*/migrations/*.pyc"  -delete
  export PGPASSWORD=mysecretpassword;
  dropdb -h 127.0.0.1 -U postgres $1
  createdb -T template0 -h 127.0.0.1 -U postgres $1
  python manage.py makemigrations
  python manage.py migrate
}
</code>