bash test 总结

Q: “glob expansion”和”pattern matching”什么区别??
A: Glob is “Unix style pathname pattern expansion”.

test [[ ]] [] 总结表格如下：

整数比较

大于	小于	等于	不等于
if [ "$a" -gt "$b" ]	if [ "$a" -gt "$b" ]	if [ "$a" -eq "$b" ]	if [ "$a" -ne "$b" ]
if [[ "$a" -gt "$b" ]]	if [[ "$a" -gt "$b" ]]	if [[ "$a" -eq "$b" ]]	if [[ "$a" -ne "$b" ]]
if ((“$a” > “$b”))	if ((“$a” < “$b”))	if ((“$a” == “$b”))	if ((“$a” != “$b”))

字符串比较

大于	小于	等于	不等于
if [ "$a" \> "$b" ]	if [ "$a" \< "$b" ]	if [ "$a" = "$b" ] if [ "$a" == "$b" ]	if [ "$a" != "$b" ]
if [[ "$a" > "$b" ]]	if [[ "$a" < "$b" ]]	if [[ "$a" = "$b" ]] if [[ "$a" == "$b" ]]	if [[ "$a" != "$b" ]]

[[]]与[]的比较表格

功能	[[ ]]	[ ]	例子
字符串比较	>	\>	-
	=(or ==)	=	-
	!=	!=	-
表达式组合	&&	-a	[[ -n $var && -f $var ]] && echo “$var is a file”
	||	-o	-
模式匹配 (Pattern matching)	=(or ==)	木有	[[ $name = "a*" ]] -> the string “a*”
正则匹配(RegularExpression matching)	=~	木有	[[ $(date) =~ ^Fri\ ...\ 13 ]] && echo “It’s Friday the 13th!”

很多情况下(视实现而定)[[]]有的而[]没有的特性

特性		例子
文件或文件夹存在	-e	[[ -e $config ]] && echo ”config file exists: $config”
文件新旧比较	-nt/-ot	[[ $file0 -nt $file1 ]] && echo ”$file0 is newer than $file1″
同一个文件	-ef	[[ $input -ef $output ]] \ && { echo ”will not overwrite input file: $input”; exit 1; }
否定	!	-

还有一些很细微的区别：
1.在[[ ]]中不处理含空格的字符串(No WordSplitting)和通配符字符串匹配(glob expansion)。因此很多参数不需要用双引号包含(need not be quoted).
file=”file name”
[[ -f $file ]] && echo “$file is a file”
file=”file name”
[ -f "$file" ] && echo “$file is a file”
2.括号()在[[ ]]中不需要用\转义(need not to be escaped).
[[ -f $file1 && ( -d $dir1 || -d $dir2) ]]
[ -f "$file1" -a \( -d "$dir1" -o -d "$dir2" \) ]

逻辑组合判断的一些例子：
if [ $condition1 ] && [ $condition2 ]
if [ $condition1 -a $condition2 ]
if [[ $condition1 && $condition2 ]]
if [ $condition1 ] || [ $condition2 ]
if [ $condition1 -o $condition2 ]
if [[ $condition1 || $condition2 ]] # Also works.
#The &&, ||, operators work within a [[ ]] test, despite giving an error within a [ ] construct.

 
mainly from:  
http://mywiki.wooledge.org/BashFAQ/031 
http://tldp.org/LDP/abs/html/comparison-ops.html