Afterdeclaring a string variable, use the-zoperator in anif statementto check whether a string is empty or not: MY_STRING="" if [ -z $MYSTRING ] then echo "String is empty" else echo "String is not empty" fi For more Shell scripting tips,check out or Bash/Shell scripting articles!
-z is the second supported bash string comparison operator used to check if a string is empty or not. The -z operator functions similarly like -n operator. Below is an example: Most importantly, you should add spaces around the square brackets. If there are no spaces, bash will complain ...
# remove the last character in string and return it in $rval if [ -z "$1" ]; then # empty string rval="" return fi # wc puts some space behind the output this is why we need sed: numofchar=`echo -n "$1" | wc -c | sed 's/ //g' ` if [ "$numofchar" = "1" ]...
#文件测试操作-d FILE_NAM # TrueifFILE_NAM is a directory-e FILE_NAM # TrueifFILE_NAM exists-f FILE_NAM # TrueifFILE_NAM existsandis a regular file-r FILE_NAM # TrueifFILE_NAM is readable-s FILE_NAM # TrueifFILE_NAM existsandisnotempty...
A null or empty ("") String will return false. StringUtils.contains(null, *) = false StringUtils.contains("", *) = false StringUtils.contains("abc", 'a') = true StringUtils.contains("abc", 'z') = false Parameters: str - the String to check, may be null ...
# empty string rval="" return fi # wc puts some space behind the output this is why we need sed: numofchar=`echo -n "$1" | wc -c | sed 's/ //g' ` if [ "$numofchar" = "1" ]; then # only one char in string
the variable X is not the empty string 为何?这是因为shell将$X展开为空字符串,表达式[-n]返回真值(因为改表达式没有提供参数)。再看这个脚本: 1 2 3 4 5 #!/bin/bash X="" if[ -n"$X"];then# -n 用来检查变量是否非空 echo"the variable X is not the empty string" ...
Matches the empty string at the beginning of a line. $ Matches the empty string at the end of a line. [a-d] Matches any one character in the range a-d. Loops and Conditions A loop is a statement in a bash programming language that allows code to be repeatedly executed. You can set...
The -n and -z will also check for a string length. The -n option check for a non-zero length and the -z option check for a zero-length string. Those primaries may be useful if you intend is to check if a variable is empty or not. Though be careful if your shell script runs wi...
Unsetting BASH_XTRACEFD or assigning it the empty string causes the trace output to be sent to the standard error. Note that setting BASH_XTRACEFD to 2 (the standard error file descriptor) and then unsetting it will result in the standard error being closed. COLUMNS Used by the select ...