bash编码注意的好习惯

不可改变的全局变量

尽量少用全局变量
以大写命名
只读声明
用全局变量来代替隐晦的$0,$1等
在我的程序中常使用的全局变量:

readonly PROGNAME=$(basename $0)
readonly PROGDIR=$(readlink -m $(dirname $0))
readonly ARGS=”$@”

readonly PROGNAME=$(basename $0)
readonly PROGDIR=$(readlink -m $(dirname $0))
readonly ARGS=”$@”
一切皆是局部的

所有变量都应为局部的。

change_owner_of_file() {
local filename=$1
local user=$2
local group=$3

chown $user:$group $filename
}

change_owner_of_file() {
local filename=$1
local user=$2
local group=$3

chown $user:$group $filename
}

change_owner_of_files() {
local user=$1; shift
local group=$1; shift
local files=$@
local i

for i in $files
do
chown $user:$group $i
done
}

change_owner_of_files() {
local user=$1; shift
local group=$1; shift
local files=$@
local i

for i in $files
do
chown $user:$group $i
done
}
自注释(self documenting)的参数
通常作为循环用的变量i,把它声明为局部变量是很重要的。
局部变量不作用于全局域。

kfir@goofy ~ $ local a
bash: local: can only be used in a function
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kfir@goofy ~ $ local a
bash: local: can only be used in a function
main()

有助于保持所有变量的局部性
直观的函数式编程
代码中唯一的全局命令是:main

main() {
local files=”/tmp/a /tmp/b”
local i

for i in $files
do
change_owner_of_file kfir users $i
done
}
main

main() {
local files=”/tmp/a /tmp/b”
local i

for i in $files
do
change_owner_of_file kfir users $i
done
}
main
一切皆是函数

唯一全局性运行的代码是:
– 不可变的全局变量声明
– main()函数
保持代码整洁
过程变得清晰

main() {
local files=$(ls /tmp | grep pid | grep -v daemon)
}
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main() {
local files=$(ls /tmp | grep pid | grep -v daemon)
}

temporary_files() {
local dir=$1

ls $dir \
| grep pid \
| grep -v daemon
}

main() {
local files=$(temporary_files /tmp)
}

temporary_files() {
local dir=$1

ls $dir \
| grep pid \
| grep -v daemon
}

main() {
local files=$(temporary_files /tmp)
}
第二个例子好得多。查找文件是temporary_files()的问题而非main()的。这段代码用temporary_files()的单元测试也是可测试的。
如果你一定要尝试第一个例子,你会得到查找临时文件以和main算法的大杂烩。

test_temporary_files() {
local dir=/tmp

touch $dir/a-pid1232.tmp
touch $dir/a-pid1232-daemon.tmp

returns “$dir/a-pid1232.tmp” temporary_files $dir

touch $dir/b-pid1534.tmp

returns “$dir/a-pid1232.tmp $dir/b-pid1534.tmp” temporary_files $dir
}

test_temporary_files() {
local dir=/tmp

touch $dir/a-pid1232.tmp
touch $dir/a-pid1232-daemon.tmp

returns “$dir/a-pid1232.tmp” temporary_files $dir

touch $dir/b-pid1534.tmp

returns “$dir/a-pid1232.tmp $dir/b-pid1534.tmp” temporary_files $dir
}
如你所见,这个测试不关心main()。
调试函数

带-x标志运行程序:

bash -x my_prog.sh
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bash -x my_prog.sh
只调试一小段代码,使用set-x和set+x,会只对被set -x和set +x包含的当前代码打印调试信息。

temporary_files() {
local dir=$1

set -x
ls $dir \
| grep pid \
| grep -v daemon
set +x
}
1

temporary_files() {
local dir=$1

set -x
ls $dir \
| grep pid \
| grep -v daemon
set +x
}
打印函数名和它的参数:

temporary_files() {
echo $FUNCNAME $@
local dir=$1

ls $dir \
| grep pid \
| grep -v daemon
}

temporary_files() {
echo $FUNCNAME $@
local dir=$1

ls $dir \
| grep pid \
| grep -v daemon
}
调用函数:

temporary_files /tmp
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temporary_files /tmp
会打印到标准输出:

temporary_files /tmp
1
temporary_files /tmp
代码的清晰度

这段代码做了什么?

main() {
local dir=/tmp

[[ -z $dir ]] \
&& do_something…

[[ -n $dir ]] \
&& do_something…

[[ -f $dir ]] \
&& do_something…

[[ -d $dir ]] \
&& do_something…
}
main

main() {
local dir=/tmp

[[ -z $dir ]] \
&& do_something…

[[ -n $dir ]] \
&& do_something…

[[ -f $dir ]] \
&& do_something…

[[ -d $dir ]] \
&& do_something…
}
main
让你的代码说话:

is_empty() {
local var=$1

[[ -z $var ]]
}

is_not_empty() {
local var=$1

[[ -n $var ]]
}

is_file() {
local file=$1

[[ -f $file ]]
}

is_dir() {
local dir=$1

[[ -d $dir ]]
}

main() {
local dir=/tmp

is_empty $dir \
&& do_something…

is_not_empty $dir \
&& do_something…

is_file $dir \
&& do_something…

is_dir $dir \
&& do_something…
}
main

is_empty() {
local var=$1

[[ -z $var ]]
}

is_not_empty() {
local var=$1

[[ -n $var ]]
}

is_file() {
local file=$1

[[ -f $file ]]
}

is_dir() {
local dir=$1

[[ -d $dir ]]
}

main() {
local dir=/tmp

is_empty $dir \
&& do_something…

is_not_empty $dir \
&& do_something…

is_file $dir \
&& do_something…

is_dir $dir \
&& do_something…
}
main
每一行只做一件事

用反斜杠\来作分隔符。例如:

temporary_files() {
local dir=$1

ls $dir | grep pid | grep -v daemon
}

temporary_files() {
local dir=$1

ls $dir | grep pid | grep -v daemon
}
可以写得简洁得多:

temporary_files() {
local dir=$1

ls $dir \
| grep pid \
| grep -v daemon
}

temporary_files() {
local dir=$1

ls $dir \
| grep pid \
| grep -v daemon
}
符号在缩进行的开始
符号在行末的坏例子:(译注:原文在此例中用了temporary_files()代码段,疑似是贴错了。结合上下文,应为print_dir_if_not_empty())

print_dir_if_not_empty() {
local dir=$1

is_empty $dir && \
echo “dir is empty” || \
echo “dir=$dir”
}

print_dir_if_not_empty() {
local dir=$1

is_empty $dir && \
echo “dir is empty” || \
echo “dir=$dir”
}
好的例子:我们可以清晰看到行和连接符号之间的联系。

print_dir_if_not_empty() {
local dir=$1

is_empty $dir \
&& echo “dir is empty” \
|| echo “dir=$dir”
}

print_dir_if_not_empty() {
local dir=$1

is_empty $dir \
&& echo “dir is empty” \
|| echo “dir=$dir”
}
打印用法

不要这样做:

echo “this prog does:…”
echo “flags:”
echo “-h print help”
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echo “this prog does:…”
echo “flags:”
echo “-h print help”
它应该是个函数:

usage() {
echo “this prog does:…”
echo “flags:”
echo “-h print help”
}

usage() {
echo “this prog does:…”
echo “flags:”
echo “-h print help”
}
echo在每一行重复。因此我们得到了这个文档:

usage() {
cat <<- EOF usage: $PROGNAME options Program deletes files from filesystems to release space. It gets config file that define fileystem paths to work on, and whitelist rules to keep certain files. OPTIONS: -c --config configuration file containing the rules. use --help-config to see the syntax. -n --pretend do not really delete, just how what you are going to do. -t --test run unit test to check the program -v --verbose Verbose. You can specify more then one -v to have more verbose -x --debug debug -h --help show this help --help-config configuration help Examples: Run all tests: $PROGNAME --test all Run specific test: $PROGNAME --test test_string.sh Run: $PROGNAME --config /path/to/config/$PROGNAME.conf Just show what you are going to do: $PROGNAME -vn -c /path/to/config/$PROGNAME.conf EOF } usage() { cat <<- EOF usage: $PROGNAME options Program deletes files from filesystems to release space. It gets config file that define fileystem paths to work on, and whitelist rules to keep certain files. OPTIONS: -c --config configuration file containing the rules. use --help-config to see the syntax. -n --pretend do not really delete, just how what you are going to do. -t --test run unit test to check the program -v --verbose Verbose. You can specify more then one -v to have more verbose -x --debug debug -h --help show this help --help-config configuration help Examples: Run all tests: $PROGNAME --test all Run specific test: $PROGNAME --test test_string.sh Run: $PROGNAME --config /path/to/config/$PROGNAME.conf Just show what you are going to do: $PROGNAME -vn -c /path/to/config/$PROGNAME.conf EOF } 注意在每一行的行首应该有一个真正的制表符‘\t’。 在vim里,如果你的tab是4个空格,你可以用这个替换命令: :s/^ /\t/ 1 :s/^ /\t/ 命令行参数 这里是一个例子,完成了上面usage函数的用法。我从Kirk’s blog post – bash shell script to use getopts with gnu style long positional parameters得到这段代码 cmdline() { # got this idea from here: # http://kirk.webfinish.com/2009/10/bash-shell-script-to-use-getopts-with-gnu-style-long-positional-parameters/
local arg=
for arg
do
local delim=””
case “$arg” in
#translate –gnu-long-options to -g (short options)
–config) args=”${args}-c “;;
–pretend) args=”${args}-n “;;
–test) args=”${args}-t “;;
–help-config) usage_config && exit 0;;
–help) args=”${args}-h “;;
–verbose) args=”${args}-v “;;
–debug) args=”${args}-x “;;
#pass through anything else
*) [[ “${arg:0:1}” == “-” ]] || delim=”\””
args=”${args}${delim}${arg}${delim} “;;
esac
done

#Reset the positional parameters to the short options
eval set — $args

while getopts “nvhxt:c:” OPTION
do
case $OPTION in
v)
readonly VERBOSE=1
;;
h)
usage
exit 0
;;
x)
readonly DEBUG=’-x’
set -x
;;
t)
RUN_TESTS=$OPTARG
verbose VINFO “Running tests”
;;
c)
readonly CONFIG_FILE=$OPTARG
;;
n)
readonly PRETEND=1
;;
esac
done

if [[ $recursive_testing || -z $RUN_TESTS ]]; then
[[ ! -f $CONFIG_FILE ]] \
&& eexit “You must provide –config file”
fi
return 0
}

cmdline() {
# got this idea from here:
# http://kirk.webfinish.com/2009/10/bash-shell-script-to-use-getopts-with-gnu-style-long-positional-parameters/
local arg=
for arg
do
local delim=””
case “$arg” in
#translate –gnu-long-options to -g (short options)
–config) args=”${args}-c “;;
–pretend) args=”${args}-n “;;
–test) args=”${args}-t “;;
–help-config) usage_config && exit 0;;
–help) args=”${args}-h “;;
–verbose) args=”${args}-v “;;
–debug) args=”${args}-x “;;
#pass through anything else
*) [[ “${arg:0:1}” == “-” ]] || delim=”\””
args=”${args}${delim}${arg}${delim} “;;
esac
done

#Reset the positional parameters to the short options
eval set — $args

while getopts “nvhxt:c:” OPTION
do
case $OPTION in
v)
readonly VERBOSE=1
;;
h)
usage
exit 0
;;
x)
readonly DEBUG=’-x’
set -x
;;
t)
RUN_TESTS=$OPTARG
verbose VINFO “Running tests”
;;
c)
readonly CONFIG_FILE=$OPTARG
;;
n)
readonly PRETEND=1
;;
esac
done

if [[ $recursive_testing || -z $RUN_TESTS ]]; then
[[ ! -f $CONFIG_FILE ]] \
&& eexit “You must provide –config file”
fi
return 0
}
你像这样,使用我们在头上定义的不可变的ARGS变量:

main() {
cmdline $ARGS
}
main

main() {
cmdline $ARGS
}
main
单元测试

在更高级的语言中很重要。
使用shunit2做单元测试

test_config_line_paths() {
local s=’partition cpm-all, 80-90,’

returns “/a” “config_line_paths ‘$s /a, ‘”
returns “/a /b/c” “config_line_paths ‘$s /a:/b/c, ‘”
returns “/a /b /c” “config_line_paths ‘$s /a : /b : /c, ‘”
}

config_line_paths() {
local partition_line=”$@”

echo $partition_line \
| csv_column 3 \
| delete_spaces \
| column 1 \
| colons_to_spaces
}

source /usr/bin/shunit2

test_config_line_paths() {
local s=’partition cpm-all, 80-90,’

returns “/a” “config_line_paths ‘$s /a, ‘”
returns “/a /b/c” “config_line_paths ‘$s /a:/b/c, ‘”
returns “/a /b /c” “config_line_paths ‘$s /a : /b : /c, ‘”
}

config_line_paths() {
local partition_line=”$@”

echo $partition_line \
| csv_column 3 \
| delete_spaces \
| column 1 \
| colons_to_spaces
}

source /usr/bin/shunit2
这里是另一个使用df命令的例子:

DF=df

mock_df_with_eols() {
cat <<- EOF Filesystem 1K-blocks Used Available Use% Mounted on /very/long/device/path 124628916 23063572 100299192 19% / EOF } test_disk_size() { returns 1000 "disk_size /dev/sda1" DF=mock_df_with_eols returns 124628916 "disk_size /very/long/device/path" } df_column() { local disk_device=$1 local column=$2 $DF $disk_device \ | grep -v 'Use%' \ | tr '\n' ' ' \ | awk "{print \$$column}" } disk_size() { local disk_device=$1 df_column $disk_device 2 } DF=df mock_df_with_eols() { cat <<- EOF Filesystem 1K-blocks Used Available Use% Mounted on /very/long/device/path 124628916 23063572 100299192 19% / EOF } test_disk_size() { returns 1000 "disk_size /dev/sda1" DF=mock_df_with_eols returns 124628916 "disk_size /very/long/device/path" } df_column() { local disk_device=$1 local column=$2 $DF $disk_device \ | grep -v 'Use%' \ | tr '\n' ' ' \ | awk "{print \$$column}" } disk_size() { local disk_device=$1 df_column $disk_device 2 } 这里我有个例外,为了测试,我在全局域中声明了DF为非只读。这是因为shunit2不允许改变全局域函数

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