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_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 abash: local: can only be used in a function
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)}
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}
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}
打印函数名和它的参数:
temporary_files() { echo $FUNCNAME $@ local dir=$1 ls $dir \ | grep pid \ | grep -v daemon}
调用函数:
temporary_files /tmp
会打印到标准输出:
temporary_files /tmp
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
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
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}
可以写得简洁得多:
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"}
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"}
打印用法
不要这样做:
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"}
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}
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/
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}
你像这样,使用我们在头上定义的不可变的ARGS变量:
main() { cmdline $ARGS}main
单元测试在更高级的语言中很重要。使用shunit2做单元测试
test_config_line_paths() { local s='partition cpm-all, 80-90,' returns "/a" "config_line_paths '$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
这里是另一个使用df命令的例子:
DF=dfmock_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。原文:http://www.kfirlavi.com/blog/2012/11/14/defensive-bash-programming/译文:http://blog.jobbole.com/73257/