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" ]...
ls #文件列表wc –l filewc -w filewc -c sourcefile #计算文件行数计算文件中的单词数计算文件中的字符数cp sourcefile destfile #文件拷贝mv oldname newname #重命名文件或移动文件rm file #删除文件grep'pattern'sourcefile #在文件内搜索字符串比如:grep'se...
Check a file exists 1 2 3 4 5 6 7 1. 2. 3. 4. 5. 6. 7. #!/bin/bashif [[ -e /tmp/adb.log ]]then echo "Exists"else echo "Not Exists"fi 1. Check Empty String 1 2 3 4 5 6 1. 2. 3. 4. 5. 6. if [[ -z "$emptyString" ]]then echo "Empty"else echo "Not...
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 ...
echo "INT is empty." >&2 exit 1 fi if [ $INT -eq 0 ]; then echo "INT is zero." else if [ $INT -lt 0 ]; then echo "INT is negative." else echo "INT is positive." fi if [ $((INT % 2)) -eq 0 ]; then echo "INT is even." else echo "INT is odd." fi fi上面...
# 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
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 ...
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 specific conditions during the script execution. Loops Expla...