Linux shell script-1

introduction of
the shell script
basic sh and shell script usage
2013 usagi@WonderRabbitProject.net CC0

what's the shell script?
● it's a language
○ script language // like a C style
■ procedural model
■ function is available
■ variable is available
■ type system is not available // so text based
■ can call an external routine // system call
● it's as same the shell-self
○ APIs are commands on the system

if you learned a C style language
● control statements
○ loop
■ `for`
■ `while` // and ùntil`
○ conditional branching
■ ìf`
■ `case` // equiv switch
● function and variable
○ `f(){}` // equiv `void f(void){}`
■ how to use input params and a return? --> next!
○ ÀBC=hoge` // equiv `char* ABC = "hoge"`
■ and more --> next!!

how to use function
● how to get input params?
○ f(){ echo $1; echo $2; echo $3; }
■ it's equiv in C style:
void f(char* a, char* b, char* c)
{ puts(a); puts(b); puts(c); }
● how to put return value?
○ n/a // shell script has not C style return value!
■ but, it has return code as same the system call
● how call function?
○ f hoge fuga piyo
■ it's equiv in C style
f("hoge", "fuga", "piyo")

return value of function call
● n/a
● but, can use static variables and a trick
○ trick
# define // it's line comment use the char of `#`
f(){ echo "it's return value!"; }
# call and get return value trick with backquote '`'
RETURN_VALUE = `f`
# and print
echo $RETURN_VALUE
■ what's `$` token?
● --> it's a variable to next!

how to use a variable?
● define a variable
○ HOGE=hogehogehoge
FUGA=fugafugafuga
num_of_my_awesome_defition=123456
● reference a variable
○ echo $HOGE
echo "$HOGE-$FUGA"
echo $num_of_my_awesome_definition >> $hoge

variable tips-1
● a variable is only string type
○ abc=1234 # quiv to abc="1234"
# it's not a number
● writing rules
○ standard definition
■ abc=hogehoge # it's ok
■ abc = fugafuga # ERROR! it's a function call
# $1='=', $2='fugafuga'; hint is white-space.
○ explicit value
■ def='#abc $abc @abc' # equiv: #abc $abc @abc
■ def="#abc $abc @abc'
# equiv: #abc fugafuga @abc

variable tips-2
● implicit defined special values
○ $1 $2 $3 ...
it's params by a function call or run a script with
params.
# f(){ echo $1; }
// int main(int ac, char** params) { }
○ $#
it's number of params
# f(){ echo $#; }
// int main(int ac, char** params) { }
○ $?
it's a last result code (success or else)
# echo $?

let's run a shell script
> pwd
/home/myname
> # it's comment line
> my_awesome_variable=1234
> echo $my_awesome_variable
1234
> my_awesome_function(){ echo $1; }
> my_awesome_function hoge
hoge

save to file a shell script
> echo 'echo $1' > my_awesome.sh
> cat my_awesome.sh
echo $1

you can write with the Vim or the other text
editor as you like if you want to use.

> vim my_aersome2.sh

run a shell script from a file
● run the other process on the process
> sh my_awesome.sh hoge
hoge
> bash my_awesome.sh fuga
fuga
● run in the process
> source my_awesome.sh piyo
piyo

environment variable
● variable
○ shell-variable
it's only visible from the shell process.
> abc=hoge
> sh <-- run a child process
>> echo $abc <-- it's put the empty string
>> exit
> echo $abc <-- it's puts 'hoge'
○ environment-varialbe
it's visible from the shell and child processes.
> export abc=hoge
> sh
>> echo $abc <-- it's puts 'hoge'

shebang and executable-file
● shebang
○ > vim hoge.sh
#!/bin/sh <-- it's shebang liine
echo $1
● executable-file
○ set the executable flag
> chmod +x hoge.sh
○ run
> ./hoge.sh <-- don't forget path before filename!
■ hint: see the $PATH environment variable. it's
search path for a command on your system. and
think with a security policy.

shebang for any script-files
● shell script
#!/bin/sh
● node.js script
#!/usr/bin/node
● python script
#!/usr/bin/python
● php script
#!/usr/bin/php
● haskell script
#!/usr/bin/runhaskell
hint: > file hoge.sh

`for` statement
and an array like variable
# it's like an array separated by the space char
values='aaa bbb ccc'

# like the foreach in Java or for-in in JS
for value in $values
do
echo $value
done

`seq` command
> seq 8
1
2
3
4
5
6
7
8

`...` <-- it's the back-quote pair,
not a single-quote pair('...')
# if use the single-quote pair
> echo 'seq 512 64 768'
seq 512 64 768
# if use the back-quote pair
> echo `seq 512 64 768`
512 576 640 704 768 <-- it's like an array string

the back-quote pattern is like an eval() in JS.
it's run a text as a script code. be cautious!

`for` statement
with `seq` command and ` pattern
it's give a loop with a numeric sequence.

for value in `seq 0 15`
do
echo $value
done

`while` and ùntil` statements
● while <-- if true then loop
while true
do
echo '＼(ô^)／'
done
● until <-- if false then loop
until false
do
echo '／(ô^)＼'
done

`test` command for comparison
> test 3 -eq 4 <-- equiv (3 == 4)
> echo $?
1 <-- so false in shell-script
> test 3 -ne 4 <-- equiv (3 != 4)
> echo $?
0 <-- so true in shell-script
> test 3 -gt 4 <-- equiv (3 > 4)
> echo $?
1 <-- so false in shell-script

`test` command for file check
> test -f /proc/cpuinfo <-- is the file available
> echo $?
0
> test -d /boot <-- is the directory available
> echo $?
0

`expr` command
for calc a number from a string
# it's ng, not calc
> echo 1 + 2 + 4

# it's ok, calc
> echo `expr 1 + 2 + 4`
7
> expr 5 + ( 5 - 5 ) * 5 / 5 % 5
5
# note: ( ) * <-- need escape-sequence.

ùntil` statement
with `test`, èxpr` and ` pattern
it's give a loop with a numeric counter.

counter=15
until `test $counter -eq 0`
do
echo $counter
counter=èxpr $counter - 1`
done

`if` statement
# if.sh > source if.sh
f(){
>f0
if test $1 -lt 0
then zero
echo 'negative' >f1
elif test $1 -gt 0 positive
then
echo 'positive'
> f -1
else negative
echo 'zero'
fi
}

`case` statement
# case.sh > source case.sh
f(){
>f0
case $1 in
0) zerp
echo 'zero';; >f5
1) two-nine
echo 'one';;
[2-9])
> f -1
echo 'two-nine';; ????
default)
echo '????'
esac
}

where are more information?
all of the information is
available on the man
pages. see the man pages.
man page is the best
unified answerer for all
GNU/Linux users.

> man sh

Linux shell script-1

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