BASH

BASH Scripting

Hello World

#!/bin/bash
STR="Hello World"
echo $STR

Variables

Local Variables

#!/bin/bash
HELLO=Hello 
function hello {
        local HELLO=World
        echo $HELLO
}
echo $HELLO
hello
echo $HELLO

Boolean

#!/bin/bash
the_world_is_flat=true
# ...do something interesting...
if [ "$the_world_is_flat" = true ] ; then
    echo 'Be careful not to fall off!'
fi

Loops

While

#!/bin/bash
COUNTER=0
while [ $COUNTER -lt 10 ]; do
    echo The counter is $COUNTER
    let COUNTER=COUNTER+1
done

For

#!/bin/bash
for i in $( ls ); do
    echo item: $i
done

Example: git pull from all repositories in a pwd

for i in $( ls ); do cd $i; git pull; cd ..; done

C-like for

#!/bin/bash
for i in `seq 1 10`;
do
    echo $i
done

Until

#!/bin/bash
COUNTER=20
until [ $COUNTER -lt 10 ]; do
    echo COUNTER $COUNTER
    let COUNTER-=1
done

Conditional

if

#!/bin/bash
T1="foo"
T2="bar"
if [ "$T1" = "$T2" ]; then
    echo expresion evaluated as true
else
    echo expresion evaluated as false
fi

case

#!/bin/bash
case $yn in
    [YySs]* ) adduser $user; break;;
    [Nn]* ) echo no se creo usuario $user; break;;
    * ) echo "Elije y/n";;
esac

User Input

#!/bin/bash
while true; do
    read -p "Do you wish to install this program?" yn
    case $yn in
        [Yy]* ) make install; break;;
        [Nn]* ) exit;;
        * ) echo "Please answer yes or no.";;
    esac
done

Password prompt

read -s -p "Password: " PASSWORD

Arrays

ARRAY=(one two three)

echo ${ARRAY[*]}
one two three

echo $ARRAY[*]
one[*]

echo ${ARRAY[2]}
three

ARRAY[3]=four

echo ${ARRAY[*]}
one two three four

Functions

function quit {
    exit
}
function e {
    echo $1
}
e Hello
e World
quit
echo foo

Redirections

stdout 2 file

ls -l > ls-l.txt

stderr 2 file

grep da * 2> grep-errors.txt

stdout 2 stderr

grep da * 1>&2

stderr 2 stdout

grep * 2>&1

stderr and stdout 2 file

rm -f $(find / -name core) &> /dev/null

extras

Check if a package is installed

#!/bin/sh
debInst() {
    dpkg-query -Wf'${db:Status-abbrev}' "$1" 2>/dev/null | grep -q '^i'
}

debInst terminator

Check if a file exists

if [ -f $FILE1 ]
then
if [ -f $FILE2 ]
then
  echo OK
  # MAIN PROGRAM HERE
fi
fi

Check if directory exists

#!/bin/bash
if [ -d /opt/ ]; then
    echo "Sí, sí existe."
else
    echo "No, no existe"
fi

#-d -» Comprobar si existe determinado directorio
#-f -» Comprobar si existe determinado archivo
#-w -» Comprobar si determinado archivo tiene permisos de escritura
#-x -» Comprobar si determinado archivo tiene permisos de ejecución.

#if not: if [ ! -d /opt/ ]; then

Check user

#!/bin/bash
user=$(whoami)
if [ "$user" == "root" ]; then
   isroot=true
   echo "Eres Root! :)"
else
   isroot=false
   echo "No eres root... :'(" 
   exit
fi

Execute localScript on remote server

ssh [user]@[server] 'bash -s' < [local_script]

Remove directorys

#!/bin/sh
die () {
    echo >&2 "$@"
    exit 1
}

[ "$#" -eq 1 ] || die "1 argument required, $# provided"
echo $1 | grep -E -q '^[0-9]+$' || die "Numeric argument required, $1 provided"

while read dir 
do
    [ -d "$dir" ] || die "Directory $dir does not exist"
    rm -rf "$dir"
done <<EOF
~/myfolder1/$1/anotherfolder 
~/myfolder2/$1/yetanotherfolder 
~/myfolder3/$1/thisisafolder
EOF

Check if variable is set

if [ -z ${var+x} ]; then echo "var is unset"; else echo "var is set to '$var'"; fi

Ubuntu proxy setup

#! /bin/bash
HTTP_PROXY_HOST=proxy.example.com
HTTP_PROXY_PORT=3128
HTTPS_PROXY_HOST=proxy.example.com
HTTPS_PROXY_PORT=3128

gsettings set org.gnome.system.proxy mode manual
gsettings set org.gnome.system.proxy.http host "$HTTP_PROXY_HOST"
gsettings set org.gnome.system.proxy.http port "$HTTP_PROXY_PORT"
gsettings set org.gnome.system.proxy.https host "$HTTPS_PROXY_HOST"
gsettings set org.gnome.system.proxy.https port "$HTTPS_PROXY_PORT"

sudo sed -i.bak '/http[s]::proxy/Id' /etc/apt/apt.conf
sudo tee -a /etc/apt/apt.conf <<EOF
Acquire::http::proxy "http://$HTTP_PROXY_HOST:$HTTP_PROXY_PORT/";
Acquire::https::proxy "http://$HTTPS_PROXY_HOST:$HTTPS_PROXY_PORT/";
EOF

sudo sed -i.bak '/http[s]_proxy/Id' /etc/environment
sudo tee -a /etc/environment <<EOF
http_proxy="http://$HTTP_PROXY_HOST:$HTTP_PROXY_PORT/"
https_proxy="http://$HTTPS_PROXY_HOST:$HTTPS_PROXY_PORT/"
EOF

Git check for updates and prompt to update

#!/bin/bash
PROJECT_DIR="$HOME/cpc"
PROJECT_PYTHON_INTERPRETER="$HOME/Virtualenvs/cpc/bin/python"
TRACK_BRANCH="MacBookPablo"
TRACK_REPO="origin"


cd $PROJECT_DIR
remote_commit=$(git branch -av | sed s/*/' '/g | grep $TRACK_BRANCH | grep $TRACK_REPO | awk '{print $2}')
echo "Remote commit: $remote_commit"
local_commit=$(git branch -av | sed s/*/' '/g | grep $TRACK_BRANCH | grep -v remotes/ | awk '{print $2}')
echo "Local commit: $local_commit"


django_migrate() {
    $PROJECT_PYTHON_INTERPRETER manage.py migrate
}

update() {
    echo "Updating code"
    git pull $TRACK_REPO, $TRACK_BRANCH
    django_migrate
}


if [ "$remote_commit" = "$local_commit" ]; then
    echo "Runing latest version"
else
    while true; do
        read -p "Update available. Do you wish to update? " yn
        case $yn in
            [YySs]*) update; break;;
            [Nn]* ) echo "Skipping update..." ; break;;
            * ) echo "Choose y/n";;
        esac
    done
fi

Links

Advanced Bash-Scripting Guide