1, commonly used grammar test conditions
| test test expression | Use test commands conditional test expression, at least one space between the command and the test expression test |
| [Test expression] | Test conditions for expression by [] brackets, [] at least one space between the boundary and the test expression in brackets |
| [[Test expression]] | The condition is tested by expression [[]] double brackets, [[]] at least one space between the double brackets test expression |
| ((Test expression)) | By (()) bis test expression conditions parentheses, ()) bis ends parentheses space is not required, commonly used in Comparative integer |
Description:
- Double brackets [[]] may be a wildcard match, which is different from that of several other places grammar
- &&, ||, <,> operator can be used like double brackets [[]] in, but not to [], the general use -a, -o, -lt, -gt instead in []
For example:
1 test -f /tmp/test.txt && echo 1 || echo 0 2 [ -f /tmp/test.txt ] && echo 1 || echo 0 3 [[ -f /tmp/test.txt ]] && echo 1 || echo 0 4 ((3>2)) && echo 1 || echo 0
2, the test expression usage
2.1, file test expression
| -d file | File exists and is a directory was true |
| -f file | File exists and is a regular file True |
| -e file | True file exists, is not figuring directory or file |
| -s file | File exists and the file size is not 0 True |
| -r file | True exists and is readable, and execution of the script file is also related to user rights |
| -w file | File exists and is writable True, with user permission to execute the script also related |
| -x file | True file exists and is executable, and user permission to execute the script also related |
| -L file | File exists and is linked files True |
| f1 -nt f2 | True New file f1 f2 than the file modification time is calculated based on the file |
| f1 f2 -ot | File f1 true, according to the file modification time than file f2 old was calculated |
2.2, the string test expression
| -n "string" | If the string length is not 0, True |
| -z "string" | If the length of the string of 0 True |
| "串1" = "串2" | If the string is equal to 1 True string 2, it can be used "==" instead of "=" |
| "串1" != "串2" | If the string is not equal to 1 True 2 strings available! "==" instead of "! =" |
note:
- For string comparison, definitely more than you want to add quotation marks after the string. Such as [-n "$ string"]
- = And! = String can be used to determine whether two identical
2.3, the integer operator
| In [] and the test | In [[]] (()) and | Explanation |
| -eq | == or = | Equal, spelling is equal |
| -nq | != | Is not equal, spelling is not equal |
| -gt | > | Is greater than, is greater than spelling |
| -give | >= | Greater than or equal, is greater equal spelling |
| -lt | < | Less than, is less than spelling |
| -the | <= | Or less, is less equal spelling |
2.4 Logical Operators
| In [] and the test | In [[]] (()) and | Explanation |
| -a | && | and, with both ends are true, the result is true |
| -O | || | or, or, both ends is true, the result is true |
| ! | ! | Not, non, the opposite ends, the result is true |
2.5, the test expression differences summary
| Test expression symbol | test | [ ] | [[ ]] | (( )) |
| Whether boundary space is required | need | need | need | Do not need |
| Logical Operators | !,-to | !,-to | !、&&、|| | !、&&、|| |
| Integer Comparison operators | -eq, -ne, -lt, -gt, -ge, -the | -eq, -ne, -lt, -gt, -ge, -the | -eq, -ne, -lt, -gt, -ge, -le or =、!=、<、>、>=、<= |
=、!=、<、>、>=、<= |
| String comparison operators | =、==、!= | =、==、!= | =、==、!= | =、==、!= |
| Supports wildcards | not support | not support | stand by | not support |