bash shell test条件测试[[ ]]和[ ]异同小结

test 命令非常强大，但是很难满足其转义需求以及字符串和算术比较之间的区别。

大于	小于	等于	不等于
if [ "$a" -gt "$b" ]	if [ "$a" -lt "$b" ]	if [ "$a" -eq "$b" ]	if [ "$a" -ne "$b" ]
if [[ "$a" -gt "$b" ]]	if [[ "$a" -lt "$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" ]]

[[ ]] and []

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!”

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	!	-

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.