给大家介绍一个shell代码检查工具
首先关于shellcheck的安装，有三种方法：
1、直接copy相应shellcheck的可执行文件到bin目录下
2、更换带有shellcheck软件包的源(/etc/apt)，然后apt-get update，安装即可
3、进行编译安装，因为shellcheck是用Cabal管理和建立的，所以使用apt-get 安装cabal-install进行编译安装
而关于shellcheck的具体作用：
#### Quoting(引号)
ShellCheck can recognize several types of incorrect quoting:
echo $1 # Unquoted variables
find . -name *.ogg # Unquoted find/grep patterns
rm "~/my file.txt" # Quoted tilde expansion
v='--verbose="true"'; cmd $v # Literal quotes in variables
for f in "*.ogg" # Incorrectly quoted 'for' loops
touch $@ # Unquoted $@
echo 'Don't forget to restart!' # Singlequote closed by apostrophe
echo 'Don\'t try this at home' # Attempting to escape ' in ''
echo 'Path is $PATH' # Variables in single quotes
trap "echo Took ${SECONDS}s" 0 # Prematurely expanded trap
#### Conditionals
ShellCheck can recognize many types of incorrect test statements.
[[ n != 0 ]] # Constant test expressions
[[ -e *.mpg ]] # Existence checks of globs
[[ $foo==0 ]] # Always true due to missing spaces
[[ -n "$foo " ]] # Always true due to literals
[[ $foo =~ "fo+" ]] # Quoted regex in =~
[ foo =~ re ] # Unsupported [ ] operators
[ $1 -eq "shellcheck" ] # Numerical comparison of strings
[ $n && $m ] # && in [ .. ]
[ grep -q foo file ] # Command without $(..)
#### Frequently misused commands
ShellCheck can recognize instances where commands are used incorrectly:
grep '*foo*' file # Globs in regex contexts
find . -exec foo {} && bar {} \;# Prematurely terminated find -exec
sudo echo 'Var=42' > /etc/profile # Redirecting sudo
time --format=%s sleep 10 # Passing time(1) flags to time builtin
while read h; do ssh "$h" uptime# Commands eating while loop input
alias archive='mv $1 /backup' # Defining aliases with arguments
tr -cd '' # [] around ranges in tr
exec foo; echo "Done!" # Misused 'exec'
find -name \*.bak -o -name \*~ -delete# Implicit precedence in find
f() { whoami; }; sudo f # External use of internal functions
#### Common beginner's mistakes
ShellCheck recognizes many common beginner's syntax errors:
var = 42 # Spaces around = in assignments
$foo=42 # $ in assignments
for $var in *; do ... # $ in for loop variables
var$n="Hello" # Wrong indirect assignment
echo ${var$n} # Wrong indirect reference
var=(1, 2, 3) # Comma separated arrays
echo "Argument 10 is $10" # Positional parameter misreference
if $(myfunction); then ..; fi # Wrapping commands in $()
else if othercondition; then .. # Using 'else if'
#### Style
ShellCheck can make suggestions to improve style:
[[ -z $(find /tmp | grep mpg) ]]# Use grep -q instead
a >> log; b >> log; c >> log # Use a redirection block instead
echo "The time is `date`" # Use $() instead
cd dir; process *; cd ..; # Use subshells instead
echo $ # Use standard $((..)) instead of old $[]
echo $(($RANDOM % 6)) # Don't use $ on variables in $((..))
echo "$(date)" # Useless use of echo
cat file | grep foo # Useless use of cat
#### Data and typing errors
ShellCheck can recognize issues related to data and typing:
args="$@" # Assigning arrays to strings
files=(foo bar); echo "$files" # Referencing arrays as strings
printf "%s\n" "Arguments: $@." # Concatenating strings and arrays.
[[ $# > 2 ]] # Comparing numbers as strings
var=World; echo "Hello " var # Unused lowercase variables
echo "Hello $name" # Unassigned lowercase variables
cmd | read bar; echo $bar # Assignments in subshells
#### Robustness
ShellCheck can make suggestions for improving the robustness of a script:
rm -rf "$STEAMROOT/"* # Catastrophic rm
touch ./-l; ls * # Globs that could become options
find . -exec sh -c 'a && b {}' \; # Find -exec shell injection
printf "Hello $name" # Variables in printf format
for f in $(ls *.txt); do # Iterating over ls output
export MYVAR=$(cmd) # Masked exit codes
#### Portability
ShellCheck will warn when using features not supported by the shebang. For example, if you set the shebang to `#!/bin/sh`, ShellCheck will warn about portability issues similar to `checkbashisms`:
echo {1..$n} # Works in ksh, but not bash/dash/sh
echo {1..10} # Works in ksh and bash, but not dash/sh
echo -n 42 # Works in ksh, bash and dash, undefined in sh
trap 'exit 42' sigint # Unportable signal spec
cmd &> file # Unportable redirection operator
read foo < /dev/tcp/host/22 # Unportable intercepted files
foo-bar() { ..; } # Undefined/unsupported function name
[ $UID = 0 ] # Variable undefined in dash/sh
local var=value # local is undefined in sh
#### Miscellaneous
ShellCheck recognizes a menagerie of other issues:
PS1='\e
PATH="$PATH:~/bin" # Literal tilde in $PATH
echo {1..$n} # Works in ksh, but not bash/dash/sh
echo {1..10} # Works in ksh and bash, but not dash/sh
echo -n 42 # Works in ksh, bash and dash, undefined in sh
trap 'exit 42' sigint # Unportable signal spec
cmd &> file # Unportable redirection operator
read foo < /dev/tcp/host/22 # Unportable intercepted files
foo-bar() { ..; } # Undefined/unsupported function name
[ $UID = 0 ] # Variable undefined in dash/sh
local var=value # local is undefined in sh
#### Miscellaneous
echo {1..$n} # Works in ksh, but not bash/dash/sh
echo {1..10} # Works in ksh and bash, but not dash/sh
echo -n 42 # Works in ksh, bash and dash, undefined in sh
trap 'exit 42' sigint # Unportable signal spec
cmd &> file # Unportable redirection operator
read foo < /dev/tcp/host/22 # Unportable intercepted files
foo-bar() { ..; } # Undefined/unsupported function name
[ $UID = 0 ] # Variable undefined in dash/sh
local var=value # local is undefined in sh
#### Miscellaneous
ShellCheck recognizes a menagerie of other issues:
PS1='\e
PATH="$PATH:~/bin" # Literal tilde in $PATH
rm “file” # Unicode quotes
echo "Hello world" # Carriage return / DOS line endings
var=42 echo $var # Expansion of inlined environment
#!/bin/bash -x -e # Common shebang errors
echo $((n/180*100)) # Unnecessary loss of precision
ls *[:digit:].txt # Bad character class globs
sed 's/foo/bar/' file > file # Redirecting to input
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