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Merge pull request koalaman#1026 from PeterDaveHello/patch-1
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Enable syntax highlight in README.md code block
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@koalaman
koalaman authored Oct 16, 2017
2 parents 1491402 + 76ad5db commit 5d9cb81
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200 changes: 112 additions & 88 deletions README.md
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Expand Up @@ -148,8 +148,10 @@ On Solus:

From Docker Hub:

docker pull koalaman/shellcheck:latest # Or :v0.4.6 for a release version
docker run -v "$PWD:/mnt" koalaman/shellcheck myscript
```sh
docker pull koalaman/shellcheck:latest # Or :v0.4.6 for a release version
docker run -v "$PWD:/mnt" koalaman/shellcheck myscript
```

or use `koalaman/shellcheck-alpine` if you want a larger Alpine Linux based image to extend.

Expand Down Expand Up @@ -209,12 +211,16 @@ This will compile ShellCheck and install it to your `~/.cabal/bin` directory.

Add this directory to your `PATH` (for bash, add this to your `~/.bashrc`):

export PATH="$HOME/.cabal/bin:$PATH"
```sh
export PATH="$HOME/.cabal/bin:$PATH"
```

Log out and in again, and verify that your PATH is set up correctly:

$ which shellcheck
~/.cabal/bin/shellcheck
```sh
$ which shellcheck
~/.cabal/bin/shellcheck
```

On native Windows, the `PATH` should already be set up, but the system
may use a legacy codepage. In `cmd.exe`, `powershell.exe` and Powershell ISE,
Expand Down Expand Up @@ -242,129 +248,147 @@ So what kind of things does ShellCheck look for? Here is an incomplete list of d

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
```sh
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 $(..)
[[ "$$file" == *.jpg ]] # Comparisons that can't succeed
(( 1 -lt 2 )) # Using test operators in ((..))
```sh
[[ n != 0 ]] # Constant test expressions
[[ -e *.mpg ]] # Existence checks of globs
[[ $foo==0 ]] # Always true due to missing spaces
[[ -n "$foo " ]] # Always true due to literals
[[ $foo =~ "fo+" ]] # Quoted regex in =~
[ foo =~ re ] # Unsupported [ ] operators
[ $1 -eq "shellcheck" ] # Numerical comparison of strings
[ $n && $m ] # && in [ .. ]
[ grep -q foo file ] # Command without $(..)
[[ "$$file" == *.jpg ]] # Comparisons that can't succeed
(( 1 -lt 2 )) # Using test operators in ((..))
```

### 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 $1 /backup' # Defining aliases with arguments
tr -cd '[a-zA-Z0-9]' # [] around ranges in tr
exec foo; echo "Done!" # Misused 'exec'
find -name \*.bak -o -name \*~ -delete # Implicit precedence in find
f() { whoami; }; sudo f # External use of internal functions
```sh
grep '*foo*' file # Globs in regex contexts
find . -exec foo {} && bar {} \; # Prematurely terminated find -exec
sudo echo 'Var=42' > /etc/profile # Redirecting sudo
time --format=%s sleep 10 # Passing time(1) flags to time builtin
while read h; do ssh "$h" uptime # Commands eating while loop input
alias archive='mv $1 /backup' # Defining aliases with arguments
tr -cd '[a-zA-Z0-9]' # [] 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
array=( [index] = value ) # Incorrect index initialization
echo "Argument 10 is $10" # Positional parameter misreference
if $(myfunction); then ..; fi # Wrapping commands in $()
else if othercondition; then .. # Using 'else if'
```sh
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
array=( [index] = value ) # Incorrect index initialization
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 $[1+2] # 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
```sh
[[ -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 $[1+2] # 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
declare -A arr=(foo bar) # Associative arrays without index
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 $bar # Assignments in subshells
```sh
args="$@" # Assigning arrays to strings
files=(foo bar); echo "$files" # Referencing arrays as strings
declare -A arr=(foo bar) # Associative arrays without index
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
```sh
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
[ $UID = 0 ] # Variable undefined in dash/sh
local var=value # local is undefined in sh
time sleep 1 | sleep 5 # Undefined uses of 'time'
```sh
echo {1..$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
time sleep 1 | sleep 5 # Undefined uses of 'time'
```
### Miscellaneous
ShellCheck recognizes a menagerie of other issues:
PS1='\e[0;32m\$\e[0m ' # PS1 colors not in \[..\]
PATH="$PATH:~/bin" # Literal tilde in $PATH
rm “file” # Unicode quotes
echo "Hello world" # Carriage return / DOS line endings
echo hello \ # Trailing spaces after \
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
```sh
PS1='\e[0;32m\$\e[0m ' # PS1 colors not in \[..\]
PATH="$PATH:~/bin" # Literal tilde in $PATH
rm “file” # Unicode quotes
echo "Hello world" # Carriage return / DOS line endings
echo hello \ # Trailing spaces after \
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
```
## Testimonials
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