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bash-scripting-slides.html
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bash-scripting-slides.html
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<!DOCTYPE html>
<html>
<head>
<title>advanced bash scripting</title>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
<style type="text/css">
@import url(http://fonts.googleapis.com/css?family=Yanone+Kaffeesatz);
@import url(http://fonts.googleapis.com/css?family=Droid+Serif:400,700,400italic);
@import url(http://fonts.googleapis.com/css?family=Ubuntu+Mono:400,700,400italic);
body {
font-family: 'Droid Serif';
font-size: medium;
}
h1, h2, h3 {
font-family: 'Yanone Kaffeesatz';
font-weight: normal;
font-size: medium;
}
.remark-code, .remark-inline-code {
font-family: 'Ubuntu Mono';
font-size: 25px;
}
.warn {
color: #fa0000;
font-weight: bold;
font-size: 25px;
}
.small {
font-size: 12px;
}
</style>
</head>
<body>
<textarea id="source">
class: center, middle
# advanced bash scripting
.small[christoph.gysin@ericsson.com]
---
# introduction
```bash
$ echo "Hello, world!"
```
```bash
Hello, world!
```
---
# variables
```bash
$ foo=bar
```
```bash
$ foo=bar
```
```bash
$ echo ${foo}
```
```bash
bar
```
---
# variables
```bash
$ message="Hello"
```
```bash
$ echo ${message}
```
```bash
Hello
```
```bash
$ message+=", world!"
```
```bash
$ echo ${message}
```
```bash
Hello, world!
```
---
# variables
```bash
$ message="x x"
```
```bash
$ echo ${message}
```
```bash
x x
```
```bash
$ echo "${message}"
```
```bash
x x
```
---
# variables
```bash
$ string="abcdefg"
```
```bash
$ echo ${string:3}
```
```bash
defg
```
```bash
$ echo ${string:4:2}
```
```bash
ef
```
```bash
$ echo ${string: -1}
```
```bash
g
```
---
# quoting
```bash
$ string="abcdefg"
```
```bash
$ echo "\$string"
```
```bash
$string
```
```bash
$ echo '$string'
```
```bash
$string
```
---
# quoting
```bash
$ msg=$'Hello,\nWorld!'
```
```bash
$ echo "${msg}"
```
```bash
Hello,
World!
```
```bash
$ echo $'\U1f60e'
```
```bash
😎
```
---
# translation
```bash
$ echo $"Hello, World!"
```
```bash
Hello, World!
```
.warn[unsafe, discouraged!]
---
# special variables
```bash
$ echo ${USER}
```
```bash
chris
```
```bash
$ echo ${BASH_VERSION}
```
```bash
4.3.27(1)-release
```
```bash
$ echo $$
```
```bash
1568
```
---
# special variables
```bash
$ echo $?
```
```bash
0
```
```bash
$ false
```
```bash
$ echo $?
```
```bash
1
```
---
# special variables
```bash
$ echo $0
```
```bash
/bin/bash
```
```bash
$ echo $1
```
```bash
```
---
# special variables
```bash
$ bash -c 'echo $1' foo bar baz
```
```bash
bar
```
```bash
$ bash -c 'echo $@' foo bar baz
```
```bash
bar baz
```
```bash
$ bash -c 'echo $0 $@' foo bar baz
```
```bash
foo bar baz
```
---
# special variables
```bash
$ bash -c 'echo $#' foo bar baz
```
```bash
2
```
---
# arrays
```bash
$ a=(abc def)
```
```bash
$ echo ${a}
```
```bash
abc
```
```bash
$ echo ${a[1]}
```
```bash
def
```
```bash
$ echo ${a[@]}
```
```bash
abc def
```
---
# arrays
```bash
$ a=(a b c)
```
```bash
$ a+=(d e f)
```
```bash
$ echo "${a[@]}"
```
```bash
a b c d e f
```
---
# arrays
```bash
$ a=(a b c)
```
```bash
$ a+=d
```
```bash
$ echo "${a[@]}"
```
```bash
ad b c
```
```bash
$ a+=(d)
```
```bash
$ echo "${a[@]}"
```
```bash
$ ad b c d
```
---
# arrays
```bash
$ a=(a b c d e f g)
```
```bash
$ echo ${#a[@]}
```
```bash
7
```
```bash
$ echo ${a[@]:2}
```
```bash
c d e f g
```
```bash
$ echo ${a[@]:2:3}
```
```bash
c d e
```
---
# associative arrays
```bash
$ unset a
```
```bash
$ declare -A a
```
```bash
$ a=([name]=bob [age]=21)
```
```bash
$ echo ${a[name]}
```
```bash
bob
```
```bash
$ echo ${a[age]}
```
```bash
21
```
---
# associative arrays
```bash
$ a[age]=23
```
```bash
$ a[email]=bob@domain.tld
```
```bash
$ echo ${a[email]}
```
```bash
bob@domain.tld
```
---
# integer
```bash
$ declare -i int
```
```bash
$ int=foo
```
```bash
$ echo ${int}
```
```bash
0
```
```bash
int=2+2
```
```bash
$ echo ${int}
```
```bash
4
```
---
# uppercase
```bash
$ declare -u upper
```
```bash
$ upper="Hello, World!"
```
```bash
$ echo ${upper}
```
```bash
HELLO, WORLD!
```
---
# functions
```bash
$ function greeter() { echo "Hello ${USER}!"; }
```
```bash
$ greeter
```
```bash
Hello chris!
```
```bash
$ function greeter() { echo "Hello $1!"; }
```
```bash
$ greeter bob
```
```bash
Hello bob!
```
---
# functions
```bash
$ function func() { return 0; }
$ func; echo $?
```
```bash
0
```
---
# functions
```bash
$ function func() { return 1; }
$ func; echo $?
```
```bash
1
```
---
# functions
```bash
$ function func() { return -1; }
$ func; echo $?
```
```bash
255
```
---
# functions
```bash
$ function func() { return 256; }
$ func; echo $?
```
```bash
0
```
---
# functions
```bash
$ function func() { return; }
$ func; echo $?
```
```bash
0
```
---
# functions
```bash
$ function func() { false; return; }
$ func; echo $?
```
```bash
1
```
---
name: local
# local variables
```bash
$ foo=1
```
```bash
$ function f() {
foo=2
}
```
```bash
$ f
```
```bash
$ echo ${foo}
```
```bash
2
```
---
# local variables
```bash
$ function f() {
echo before: ${foo}
local foo=3
echo after: ${foo}
}
```
```bash
$ f
```
```bash
before: 2
after: 3
```
```bash
$ echo ${foo}
```
```bash
2
```
---
# lists
```bash
$ echo foo; echo bar
```
```bash
foo
bar
```
```bash
$ true && echo "it's true!"
```
```bash
it's true!
```
```bash
$ false && echo "is it?" || echo "nope, that's false"
```
```bash
nope, that's false
```
---
# test
```bash
$ test foo = foo; echo $?
```
```bash
0
```
```bash
$ test foo = foo && echo true || echo false
```
```bash
true
```
```bash
$ test foo = bar && echo true || echo false
```
```bash
false
```
---
# test
```bash
$ test foo = bar
```
```bash
$ [ foo = bar ]
```
```bash
$ [ foo = bar ] && echo true || echo false
```
```bash
false
```
---
# test
```bash
[ ! <expression> ] # expression is false
```
```bash
[ <expr1> -a <expr2> ] # both are true
```
```bash
[ <expr1> -o <expr2> ] # either is true
```
```bash
[ -n <string> ] # string length is nonzero
```
```bash
[ -z <string> ] # string length is zero
```
```bash
[ <string1> = <string2> ] # strings are equal
```
```bash
[ <string1> != <string2> ] # strings are not equal
```
---
# test
```bash
[ <int1> -eq <int2> ] # integers are equal
```
```bash
[ <int1> -ne <int2> ] # integers are not equal
```
```bash
[ <int1> -lt <int2> ] # int1 is less than int2
```
```bash
[ <int1> -le <int2> ] # int1 is less or equal int2
```
```bash
[ <int1> -gt <int2> ] # int1 is greater than int2
```
```bash
[ <int1> -ge <int2> ] # int1 is greater or equal int2
```
---
# test
```bash
[ -e <file> ] # file exists
```
```bash
[ -f <file> ] # file exists and is a regular file
```
```bash
[ -L <file> ] # file exists and is a symbolic link
```
```bash
[ -d <file> ] # file exists and is a directory
```
```bash
[ -s <file> ] # file exists and has size greater than 0
```
```bash
[ -r <file> ] # file exists and is readable
```
```bash
[ -x <file> ] # file exists and is executable
```
---
# control structures: if/elif/else/fi
```bash
$ function f() {
if [ $1 -lt 0 ]; then
echo "negative"
elif [ $1 -le 9 ]; then
echo "one digit"
elif [ $1 -le 99 ]; then
echo "two digits"
else
echo "large!"
fi
}
```
```bash
$ f 5
```
```bash
one digit
```
---
# control structures: if/elif/else/fi
```bash
$ function f() {
if [ $1 -lt 0 ]; then
echo "negative"
elif [ $1 -le 9 ]; then
echo "one digit"
elif [ $1 -le 99 ]; then
echo "two digits"
else
echo "large!"
fi
}
```
```bash
$ f -1
```
```bash
negative
```
---
# control structures: if/elif/else/fi
```bash
$ function f() {
if [ $1 -lt 0 ]; then
echo "negative"
elif [ $1 -le 9 ]; then
echo "one digit"
elif [ $1 -le 99 ]; then
echo "two digits"
else
echo "large!"
fi
}
```
```bash
$ f 2134567890
```
```bash
large!
```
---
# control structures: while/do/done
```bash
$ function f() {
local -i i=0
local args=($@)
while [ ${i} -lt $# ]; do
echo "${i}: ${args[${i}]}"
i=i+1
done
}
```
```bash
$ f foo bar baz
```
```bash
0: foo
1: bar
2: baz
```
---
# control structures: case/in/esac
```bash
$ function nth() {
case ${1: -1} in
1) echo "${1}st" ;;
2) echo "${1}nd" ;;
3) echo "${1}rd" ;;
[4-9]) echo "${1}th" ;;
*) echo "not a number" ;;
esac
}
```
```bash
$ nth 3
```
```bash
3rd
```
---
# control structures: case/in/esac
```bash
$ function nth() {
case ${1: -1} in
1) echo "${1}st" ;;
2) echo "${1}nd" ;;
3) echo "${1}rd" ;;
[4-9]) echo "${1}th" ;;
*) echo "not a number" ;;
esac
}
```
```bash
$ nth 105
```
```bash
105th
```
---
# control structures: case/in/esac
```bash
$ function nth() {
case ${1: -1} in
1) echo "${1}st" ;;
2) echo "${1}nd" ;;
3) echo "${1}rd" ;;
[4-9]) echo "${1}th" ;;
*) echo "not a number" ;;
esac
}
```
```bash
$ nth foo
```
```bash
not a number
```
---
# control structures: for/do/done
```bash
$ for((i=1; i<=5; ++i)); do
echo ${i}
done
```
```bash
1
2
3
4
5
```
---
# control structures: for/in/do/done
```bash
$ for number in 1 2 3 4 5; do
echo ${number}
done
```
```bash
1
2
3
4
5
```
---
# control structures: for/in/do/done
```bash
$ names=("Alice" "Bob jr." "Carol" "Dave")
```
```bash
$ for name in ${names[@]}; do # careful!
echo ${name}
done
```
```bash
Alice
Bob
jr.
Carol
Dave
```
---
# control structures: for/in/do/done
```bash
$ names=("Alice" "Bob jr." "Carol" "Dave")
```
```bash
$ for name in "${names[@]}"; do
echo ${name}
done
```
```bash
Alice
Bob jr.
Carol
Dave
```
---
# command substitution
```bash
$ date +%s
```
```bash
1412160589
```
```bash
$ seconds=$(date +%s)
```
```bash
$ echo ${seconds}
```
```bash
1412160713
```
---
# command substitution
```bash
$ cat /etc/hostname
```
```bash
echrgys-laptop
```
```bash
$ hostname=$(cat /etc/hostname) # slow!
```
```bash
$ hostname=$(</etc/hostname)
```
```bash
$ echo ${hostname}
```
```bash
echrgys-laptop
```
---
# compound commands: group
```bash
$ { echo a; echo b }
```
```bash
a
b
```
```bash
$ f=file.txt
$ [ -f ${f} ] || { echo "creating file"; touch ${f}; }
```
---
# compound commands: subshell
```bash
$ pwd
/home/chris
```
```bash
$ (cd /tmp; touch temp.txt)
```
```bash
$ pwd
/home/chris
```
```bash
$ ls /tmp/*.txt
/tmp/temp.txt
```
---
# compound commands: subshell
```bash
$ i=1
```
```bash
$ (i=2)
```
```bash
$ echo $i
```
```bash
1
```
---
# pipelines
```bash
$ (echo abc; echo def; echo ghi)
```
```bash
abc
def
ghi
```
```bash
$ (echo abc; echo def; echo ghi) | tac
```
```bash
ghi
def
abc
```
---
# pipelines
```bash
$ (echo abc; echo def; echo ghi) | tac | rev
```