bash shell test條件測試[[ ]]和[ ]異同小結

test 命令非常強大，但是很難滿足其轉義需求以及字串和算術比較之間的區別。

大於	小於	等於	不等於
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”))

字串比較

大於	小於	等於	不等於
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
字串比較	>	\>	-
=(or ==)	=	-
!=	!=	-
運算式組合	&&	-a	[[ -n $var && -f $var ]] && echo “$var is a file”
||	-o	-
模式比對 (Pattern matching)	=(or ==)	木有	[[ $name = "a*" ]] -> the string “a*”
正則匹配(RegularExpression matching)	=~	木有	[[ $(date) =~ ^Fri\ ...\ 13 ]] && echo “It’s Friday the 13th!”

特性		例子
檔案或檔案夾存在	-e	[[ -e $config ]] && echo ”config file exists: $config”
檔案新舊比較	-nt/-ot	[[ $file0 -nt $file1 ]] && echo ”$file0 is newer than $file1″
同一個檔案	-ef	[[ $input -ef $output ]] \ && { echo ”will not overwrite input file: $input”; exit 1; }
否定	!	-

邏輯組合判斷的一些例子：
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.

大於	小於	等於	不等於
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”))

字串比較

大於	小於	等於	不等於
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
字串比較	>	\>	-
=(or ==)	=	-
!=	!=	-
運算式組合	&&	-a	[[ -n $var && -f $var ]] && echo “$var is a file”
||	-o	-
模式比對 (Pattern matching)	=(or ==)	木有	[[ $name = "a*" ]] -> the string “a*”
正則匹配(RegularExpression matching)	=~	木有	[[ $(date) =~ ^Fri\ ...\ 13 ]] && echo “It’s Friday the 13th!”

特性		例子
檔案或檔案夾存在	-e	[[ -e $config ]] && echo ”config file exists: $config”
檔案新舊比較	-nt/-ot	[[ $file0 -nt $file1 ]] && echo ”$file0 is newer than $file1″
同一個檔案	-ef	[[ $input -ef $output ]] \ && { echo ”will not overwrite input file: $input”; exit 1; }
否定	!	-

邏輯組合判斷的一些例子：
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.