Bash

manual, refs

• Mendel Cooper - Advanced Bash-Scripting Guide (aka. ABS) (한글판)
• Bash Reference Manual
• bash features
• BASH Programming - Introduction HOW-TO ★
• Bash Guide for Beginners
• Bash scripting Tutorial

\$SHLVL

The variable tracks your shell nesting level

\$ echo \$SHLVL
1
\$ bash
\$ echo \$SHLVL
2
\$ exit
\$ echo \$SHLVL
1

http://stackoverflow.com/a/4511483/766330

Regular expression match test

Use double bracket and =~

if [[ \$gg =~ ^....grid.*\$ ]] ; then echo \$gg; fi

[1]

if you want use a wildcard, do like this

[[ sed-4.2.2.tar.bz2 == *tar.bz2 ]] && echo matched

[2]

! is a negation. Like this,

[[ ! sed-4.2.2.tar.bz2 == *tar.bz2 ]]

getopt

long options

use getopt(not getopts) [3]
getopts가 builtin이다. getopt는 쓰지 않는것을 권장한(다는 얘기도 있고 아니라는 얘기도 있고 그렇)다. ref) getopt vs getopts

multiple arguments with one flag

깔끔한 방법이 없어보임. [4]

-o a1 -o a2 -o a3

이런식으로 계속 주는 수밖에 없는듯

simple example

http://www.bahmanm.com/blogs/command-line-options-how-to-parse-in-bash-using-getopt

default option getopt

 $ getopt -s bash -o l:: -l list:: -- -ltest
  -l 'test' --
 $ getopt -s bash -o l:: -l list:: -- --list foo
  --list '' -- 'foo'
 $ getopt -s bash -o l:: -l list:: -- --list=foo
  --list 'foo' --

::을 쓰면 되지만, optional argument를 명시할 때는 short option의 경우 option뒤에 바로 붙여야 하고 long option의 경우 =을 꼭 써주어야 한다. [5]

긴 옵션만 쓸 때 주의

\$ getopt -l test: -- --test abc
 'abc' --
\$ getopt -o x -l test: -- --test abc
 --test 'abc' --

매뉴얼에 보면,

If no '-o' or '--options' option is found in the first part, the first parameter of the second part is used as the short options string.

결론: 헷갈리고 싶지 않으면 -o로 암거나 넣을것.

About eval set --

getopt(s)다음에 eval set을 하는 이유 참고. Bash: Preserving Whitespace Using set and eval
set뒤에 오는것은 argument가 되고, eval은 말그대로 eval. 여기서는 tricky하게 쓰이는 것으로 side effect가깝다. set만 쓰면 아예 아무것도 하지 않은 것과 동일한 결과를 보여준다.

stty

터미널이 제정신이 아닌것 같다 싶으면 그냥

stty sane

이 외 다양한 옵션에 관해서는 링크참고

bash expansion : ranges

\$ echo {d..h}
d e f g h

\$ echo {d..Z}
d c b a _ ^ ]  [ Z

For more information, refer wiki.bash-hackers.org.

redirection

### cp file1 file2와 같다
\$ cat < file1 > file2

string : $''

\$ # Single quotation in single qoute
\$ # http://stackoverflow.com/a/16605140/766330
\$ echo \'sdlfkjsldf\' | sed \$'s/\'//'
sdlfkjsldf'
\$ #   \$'string' : this is special.
\$ #   below line won't work.
\$ #   echo \'sdlfkjsldf\' | sed 's/\'//‘

[6]

or

\$ # 'or' 
\$ if [ -z "$1" ] || [ -z "$2" ]; then
>    echo "Usage: `basename $0` rslt_file target_folder"
> fi

ref. expressions used with if

extract tar archive from stdin

use - as the input file

cat largefile.tgz.aa largefile.tgz.ab | tar zxf -

[7]

find out what is using TCP port 80

# netstat -tulpn | grep :80

-p : You should be root

[8]

read from file or stdin (default argument)

while read line 
do
  echo "$line"
done < "${1:-/dev/stdin}"

${1:-…} takes $1 if defined otherwise the file name of the standard input of the own process is used

http://stackoverflow.com/a/7045517/766330

default value syntax

${1:-foo}

\$1이 unset이거나 null이면 foo가 된다.

${1-foo}

\$1으로 empty string(=null)이 가능하다. set 여부만 체크

https://stackoverflow.com/a/9333006/766330

emulating do while loop

Place the body of your loop after the while and before the test.

while 
    check_if_file_present
    #do other stuff
    (( current_time <= cutoff ))
do
    :
done

http://stackoverflow.com/a/16491478/766330

no op

:

$ if true; then :; else echo; fi

[9]

Default .bashrc

/etc/skel/.bashrc

[10]

Tar the output on the fly

The same -f - option works for tarring as well.

tar -cf - something | tar -C somefolder -xvf -

GNU tar uses stdio by default:

tar -c something | tar -C somefolder -xv

[11]

Useful date format

 
 $ date +%D
 04/11/17
 $ date +%F
 2017-04-11
 $ date +%R
 18:15
 $ date +%T
 18:15:47

max numeric value

$ echo $((2**63 -1))
9223372036854775807
$ echo $((2**63 ))
-9223372036854775808

https://superuser.com/a/1030129/108174

Get the name of the caller

The \$PPID variable holds the parent process ID. So you could parse the output from ps to get the command.

PARENT_COMMAND="$(ps -o comm= $PPID)"

Replace comm= with args=to get the full command line (command + arguments). The = alone is used to suppress the headers. http://stackoverflow.com/a/26985984/766330

Count occurrences of a character

use grep -o

 needle=","
 var="text,text,text,text"

 number_of_occurrences=$(grep -o "$needle" <<< "$var" | wc -l)

http://stackoverflow.com/a/16679459/766330
About <<< sign, refer here strings

head and tail of a file ★

(head; tail) < file.txt

http://stackoverflow.com/a/8624829/766330

To pipe stderr, and not stdout

First redirect stderr to stdout — the pipe; then redirect stdout to /dev/null (without changing where stderr is going):

command 2>&1 >/dev/null | grep 'something’

순서를 바꾸면 안된다. 2>&1이 먼저 와야 한다.

https://stackoverflow.com/a/2342841/766330

nohup to already-running process

1

c-z
bg
disown -h job#
            eg. %1, %2, ...

jobs command shows this number.

2

c-z
# @ another terminal
kill -20 PID #SIGTSTP : suspend process
kill -18 PID #SIGCONT

inspecting a text file

xxd
hexdump -C
cat -v
sed -n l

Array

declare, add:

AR[idx]=VAL

zero base.

declare -a AR
AR=(V1 V2 V3 VN)

 echo ${AR[*]}
=echo ${AR[@]}

unset AR[1]

해당 index가 비는 것. rearrange되지 않는다.

Comparing strings

String 비교시 =앞 뒤 공백 주의. 붙여쓰면 assign.

String의 경우 =와 ==는 같다.

Regex: Match NOT curved or square bracket

\\[[^\\[\\]]+\\]

https://stackoverflow.com/a/15221304/766330