Bash 간단한 내용 정리

 

출처 : http://invisiblepixels.org/lang/bash.html

 

Contents:

1. History
2. Built in Variables
3. Logical Comparisons
4. Loops and Decisions
5. Gathering Input
6. Exit Codes
7. Redirection
8. Variable Manipulation
9. File Permissions
10. Functions
11. Arrays

History

!$	just the last word of the previous command
!!	previous command (same as up arrow)
!string	most recent command starting with string
!?string	most recent entry containing string
^str1^str2	rerun last command replacing str1 with str2

---

Built-in Variables

$#	no of args passed to the prog
$*	reference all args passed as $1, $2, $3
$@	same as $* but references as individual string "$1" "$2" "$3"
$0	is the name of the programme
$$	process id of programme being executed
$!	process id of last prog sent to background for execution
$?	exit status of last command not in bg
$-	current shell options in effect. see SET
IFS	Internal Field Separator. What separates words (doesn't have to be a space)

---

Logical Comparisons

String Tests = equals != not equal to < Sorts lower > Sorts higher -z zero characters long -n 1 more characters long string string is not null

Integer Tests -eq equals -ne not equal to -lt less than < -gt greater than > -le less than or equal to -ge greater than or equal to

Logic && logical AND || logical OR -a boolean and -o boolean or

File Tests -e exists at all -f is ordinary file -d is directory -r file is readable -w file is writable -x file is executable -s non empty

File Comparisons -nt is file newer (checks modification date) -ot is file older (checks modification date)

---

Loops and Decisions

if case if decision then     statements elif decision     then         statements else     statements fi case string in regexp)     statements ;; regexp)     statements ;; *)     statements esac

for for var in list do     statements done while while decision do     statements done until until decision do     statements done

---

Gathering Input read
getopts

---

Exit Codes Success: $? = 0
Failure: $? != 0

---

Redirection

** 1 = STDOUT    2 = STDERR **
command 2>filename	redirects STDERROR
command >&2	redirect *to* STDERROR. ie echo hello >&2 sends hello to stderror
command >foo 2>&1	redirects STDOUT to foo and STDERROR to STDOUT (which in this case is foo)
>&-	causes STDOUT to go nowhere (cyberspace)
<&-	causes input to come from nowhere. ie there is no input

---

Variable Manipulation

${var}	curlies delimit var name
${var:-string}	returns the string if var is empty
${var:=string}	returns the string if var empty AND var is assigned the value of string
${#var}	returns the length of the contents of var. or if #@ then returns no of elements in $@
${var:?string}	returns string if var empty. also prints the name of var
${var:+string}	returns string if variable is set. otherwise returns blank

---

File Permissions

perm octal notes r 4   w 2   x 1   s-- 4--- SetUid. -s- 2--- SetGid. --t 1--- StickyBit.

Who function What u g o a + (add to existing) - (remove from existing) = (replace existing) r w x s t

---

Functions

functionname() {
local var1

statements
}

can pass parameters to it when calling it. ie functionname a b c
to terminate a function use the return n command, not exit. exit will kill the whole programme.

---

Arrays

Declare:

• (Note: in that the first two examples, because you have declared the indices, you can list the elements in any random order)
  

  days[0]=Sunday
  days[1]=Monday
  days[2]=Tuesday
  

• months=([01]=Jan [02]=Feb [03]=Mar)

• With no indices declared, the elements are automatically assigned consecutive indices starting from [0].
  If you assign one of the elements an index, for example if you give autumn the index of [8]=autumn,
  all the entries following autumn will be given consecutive indices, starting from that point.

  seasons=(summer autumn winter spring)

Accessing:

• for counter in 1 2 3 4
  do
      echo "${seasons[$counter]}"
  done
  

• echo ${seasons[@]} or echo $seasons[*]
  The @ and * work the same way they do as $@ and $* (see top of page)

Length / Number of Elements:

• To find out the number of non-null elements in an array: length=${#array[@]}

  If you've set up an array like this: seasons=(summer autumn [6]=winter spring),
  even though winter has an index of [6] and spring [7], ${#array[@]} will only return a value of 4.

• To find out the length of an individual element: length=${#array[5]}

 

 

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