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 | - | |
| (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 || $condition2 ]] # Also works.
#The &&, ||, operators work within a [[ ]] test, despite giving an error within a [ ] construct.
| 大于 | 小于 | 等于 | 不等于 |
| if [ "$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 | - | |
| (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.
总结
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