Bash速查表

例

#!/usr/bin/env bash

NAME="John"
echo "Hello $NAME!"

變量

NAME="John"
echo $NAME
echo "$NAME"
echo "${NAME}!"

字符串引號

NAME="John"
echo "Hi $NAME"  #=> Hi John
echo 'Hi $NAME'  #=> Hi $NAME

條件執行

git commit && git push
git commit || echo "Commit failed"

功能

get_name() {
  echo "John"
}

echo "You are $(get_name)"

Shell執行

echo "I'm in $(pwd)"
echo "I'm in `pwd`"
# Same

條件語句

if [[ -z "$string" ]]; then
  echo "String is empty"
elif [[ -n "$string" ]]; then
  echo "String is not empty"
fi

擴展

echo {A,B}.js
{A,B}    與...同樣 A B
{A,B}.js    與...同樣 A.js B.js
{1..5}    與...同樣 1 2 3 4 5

嚴格的模式

set -euo pipefail
IFS=$'\n\t'

參數擴展

基本

name="John"
echo ${name}
echo ${name/J/j}    #=> "john" (substitution)
echo ${name:0:2}    #=> "Jo" (slicing)
echo ${name::2}     #=> "Jo" (slicing)
echo ${name::-1}    #=> "Joh" (slicing)
echo ${name:(-1)}   #=> "n" (slicing from right)
echo ${name:(-2):1} #=> "h" (slicing from right)
echo ${food:-Cake}  #=> $food or "Cake"

length=2
echo ${name:0:length}  #=> "Jo"

STR="/path/to/foo.cpp"
echo ${STR%.cpp}    # /path/to/foo
echo ${STR%.cpp}.o  # /path/to/foo.o

echo ${STR##*.}     # cpp (extension)
echo ${STR##*/}     # foo.cpp (basepath)

echo ${STR#*/}      # path/to/foo.cpp
echo ${STR##*/}     # foo.cpp

echo ${STR/foo/bar} # /path/to/bar.cpp
STR="Hello world"
echo ${STR:6:5}   # "world"
echo ${STR:-5:5}  # "world"
SRC="/path/to/foo.cpp"
BASE=${SRC##*/}   #=> "foo.cpp" (basepath)
DIR=${SRC%$BASE}  #=> "/path/to/" (dirpath)

代換

${FOO%suffix}    刪除後綴
${FOO#prefix}    刪除前綴
${FOO%%suffix}    刪除長後綴
${FOO##prefix}    刪除長前綴
${FOO/from/to}    替換第一場比賽
${FOO//from/to}    所有替換
${FOO/%from/to}    替換後綴
${FOO/#from/to}    替換前綴

長度

${#FOO}    的長度 $FOO

解釋

# Single line comment
: '
This is a
multi line
comment
'

子

${FOO:0:3}    子串（位置，長度）
${FOO:-3:3}    來自右邊的子串

默認值

${FOO:-val}    $FOO，或者val若是沒有設置
${FOO:=val}    設置$FOO到val若是沒有設置
${FOO:+val}    val若是$FOO設置
${FOO:?message}    顯示錯誤消息，若是$FOO未設置則退出

循環

循環基礎

for i in /etc/rc.*; do
  echo $i
done

for循環

for ((i = 0 ; i < 100 ; i++)); do
  echo $i
done

for i in {1..5}; do
    echo "Welcome $i"
done
步長
for i in {5..50..5}; do
    echo "Welcome $i"
done

死循環

while true; do
  ···
done

行循環

< file.txt | while read line; do
  echo $line
done

函數

定義函數

myfunc() {
    echo "hello $1"
}
# Same as above (alternate syntax)
function myfunc() {
    echo "hello $1"
}
myfunc "John"

參數

$#    參數數量
$*    全部參數
$@    全部參數，從第一個開始
$1    第一個參數

返回

myfunc() {
    local myresult='some value'
    echo $myresult
}
result="$(myfunc)"

提出錯誤

myfunc() {
  return 1
}
if myfunc; then
  echo "success"
else
  echo "failure"
fi

條件

條件

[[ -z STRING ]]    空字符串
[[ -n STRING ]]    不是空字符串
[[ STRING == STRING ]]    等於
[[ STRING != STRING ]]    不平等
[[ NUM -eq NUM ]]    等於
[[ NUM -ne NUM ]]    不相等
[[ NUM -lt NUM ]]    少於
[[ NUM -le NUM ]]    小於等於
[[ NUM -gt NUM ]]    大於
[[ NUM -ge NUM ]]    大於或等於
[[ STRING =~ STRING ]]    正則表達式
(( NUM < NUM ))   數字條件
[[ -o noclobber ]]    若是啓用了OPTIONNAME
[[ ! EXPR ]]    非
[[ X ]] && [[ Y ]]    與
[[ X ]] || [[ Y ]]    或

文件條件

[ -e FILE ]]    存在
[[ -r FILE ]]    可讀
[[ -h FILE ]]    符號連接
[[ -d FILE ]]    目錄
[[ -w FILE ]]    可寫
[[ -s FILE ]]    大小> 0字節
[[ -f FILE ]]    文件
[[ -x FILE ]]    可執行文件
[[ FILE1 -nt FILE2 ]]    1比2更新
[[ FILE1 -ot FILE2 ]]    2比1更近
[[ FILE1 -ef FILE2 ]]    相同的文件

例

if ping -c 1 google.com; then
  echo "It appears you have a working internet connection"
fi

if grep -q 'foo' ~/.bash_history; then
  echo "You appear to have typed 'foo' in the past"
fi

# String
if [[ -z "$string" ]]; then
  echo "String is empty"
elif [[ -n "$string" ]]; then
  echo "String is not empty"
fi
# Combinations
if [[ X ]] && [[ Y ]]; then
  ...
fi
# Equal
if [[ "$A" == "$B" ]]
# Regex
if [[ "A" =~ "." ]]
if (( $a < $b )); then
   echo "$a is smaller than $b"
fi
if [[ -e "file.txt" ]]; then
  echo "file exists"
fi

數組

定義數組

Fruits=('Apple' 'Banana' 'Orange')
Fruits[0]="Apple"
Fruits[1]="Banana"
Fruits[2]="Orange"

使用數組

echo ${Fruits[0]}           # Element #0
echo ${Fruits[@]}           # All elements, space-separated
echo ${#Fruits[@]}          # Number of elements
echo ${#Fruits}             # String length of the 1st element
echo ${#Fruits[3]}          # String length of the Nth element
echo ${Fruits[@]:3:2}       # Range (from position 3, length 2)

操做

Fruits=("${Fruits[@]}" "Watermelon")    # Push
Fruits+=('Watermelon')                  # Also Push
Fruits=( ${Fruits[@]/Ap*/} )            # Remove by regex match
unset Fruits[2]                         # Remove one item
Fruits=("${Fruits[@]}")                 # Duplicate
Fruits=("${Fruits[@]}" "${Veggies[@]}") # Concatenate
lines=(`cat "logfile"`)                 # Read from file

迭代

for i in "${arrayName[@]}"; do
  echo $i
done

字典

定義

declare -A sounds
sounds[dog]="bark"
sounds[cow]="moo"
sounds[bird]="tweet"
sounds[wolf]="howl"

使用詞典

echo ${sounds[dog]} # Dog's sound
echo ${sounds[@]}   # All values
echo ${!sounds[@]}  # All keys
echo ${#sounds[@]}  # Number of elements
unset sounds[dog]   # Delete dog

迭代

迭代value

for val in "${sounds[@]}"; do
  echo $val
done

迭代鍵

for key in "${!sounds[@]}"; do
  echo $key
done

選項

選項

set -o noclobber  # Avoid overlay files (echo "hi" > foo)
set -o errexit    # Used to exit upon error, avoiding cascading errors
set -o pipefail   # Unveils hidden failures
set -o nounset    # Exposes unset variables

全局選項

set -o nullglob    # Non-matching globs are removed  ('*.foo' => '')
set -o failglob    # Non-matching globs throw errors
set -o nocaseglob  # Case insensitive globs
set -o globdots    # Wildcards match dotfiles ("*.sh" => ".foo.sh")
set -o globstar    # Allow ** for recursive matches ('lib/**/*.rb' => 'lib/a/b/c.rb')

歷史

命令

history    顯示歷史
shopt -s histverify    不要當即執行擴展結果

操做

!!    再次執行最後一個命令
!!:s/<FROM>/<TO>/    在最近的命令中替換第一次出現的<FROM>to<TO>
!!:gs/<FROM>/<TO>/    在最近的命令中替換全部出現的<FROM>to<TO>
!$:t    僅從最近命令的最後一個參數擴展basename
!$:h    從最近命令的最後一個參數擴展目錄
!!而且!$能夠替換爲任何有效的擴展。

展開

!$    展開最近命令的最後一個參數
!*    展開最近命令的全部參數
!-n    展開n最近的命令
!n    n在歷史記錄中展開命令
!<command>    展開最近的命令調用 <command>

!!:n    僅從n最近的命令擴展該令牌（命令是0;第一個參數是1）
!^    從最近的命令擴展第一個參數
!$    從最近的命令擴展最後一個標記
!!:n-m    從最近的命令擴展標記範圍
!!:n-$    n從最近的命令擴展令牌到最後

雜項

數值計算

$((a + 200))      # Add 200 to $a
$((RANDOM%=200))  # Random number 0..200

檢查命令

command -V cd
#=> "cd is a function/alias/whatever"

錯誤

trap 'echo Error at about $LINENO' ERR
要麼

traperr() {
  echo "ERROR: ${BASH_SOURCE[1]} at about ${BASH_LINENO[0]}"
}

set -o errtrace
trap traperr ERR

相對路徑

source "${0%/*}/../share/foo.sh"

腳本目錄

DIR="${0%/*}"

定界符

cat <<END
hello world
END

閱讀輸入

echo -n "Proceed? [y/n]: "
read ans
echo $ans
read -n 1 ans    # Just one character

轉到上一個目錄

pwd # /home/user/foo
cd bar/
pwd # /home/user/foo/bar
cd -
pwd # /home/user/foo

子shell

(cd somedir; echo "I'm now in $PWD")
pwd # still in first directory

重定向

python hello.py > output.txt   # stdout to (file)
python hello.py >> output.txt  # stdout to (file), append
python hello.py 2> error.log   # stderr to (file)
python hello.py 2>&1           # stderr to stdout
python hello.py 2>/dev/null    # stderr to (null)
python hello.py &>/dev/null    # stdout and stderr to (null)
python hello.py < foo.txt      # feed foo.txt to stdin for python

案例/開關

case "$1" in
  start | up)
    vagrant up
    ;;

  *)
    echo "Usage: $0 {start|stop|ssh}"
    ;;
esac

打印

printf "Hello %s, I'm %s" Sven Olga
#=> "Hello Sven, I'm Olga

得到選擇

while [[ "$1" =~ ^- && ! "$1" == "--" ]]; do case $1 in
  -V | --version )
    echo $version
    exit
    ;;
  -s | --string )
    shift; string=$1
    ;;
  -f | --flag )
    flag=1
    ;;
esac; shift; done
if [[ "$1" == '--' ]]; then shift; fi

特殊變量

$?    退出上次任務的狀態
$!    最後一個後臺任務的PID
$$    shell的PID