-n is one of the supported bash string comparison operators used for checking null strings in a bash script. When -n operator is used, it returns true for every case, but that’s if the string contains characters. On the other hand, if the string is empty, it won’t return true. -...
isvalidip() #@ USAGE: isvalidip DOTTED-QUAD { case $1 in ## reject the following: ## empty string ## anything other than digits and dots ## anything not ending in a digit "" | *[!0-9.]* | *[!0-9]) return 1 ;; esac ## Change IFS to a dot, but only in this functio...
Afterdeclaring a string variable, use the-zoperator in anif statementto check whether a string is empty or not: MY_STRING="" if [ -z $MYSTRING ] then echo "String is empty" else echo "String is not empty" fi For more Shell scripting tips,check out or Bash/Shell scripting articles!
grep 'pattern' file: 在文件内搜索字符串比如:grep 'searchstring' file.txt cut -b colnum file: 指定欲显示的文件内容范围,并将它们输出到标准输出设备比如:输出每行第5个到第9个字符cut -b5-9 file.txt千万不要和cat命令混淆,这是两个完全不同的命令 cat file.txt: 输出文件内容到标准输出设备(屏幕)...
BashBites:Check Files Check a file exists 1 2 3 4 5 6 7 1. 2. 3. 4. 5. 6. 7. #!/bin/bashif [[ -e /tmp/adb.log ]]then echo "Exists"else echo "Not Exists"fi 1. Check Empty String 1 2 3 4 5 6 1. 2. 3.
the variable X is not the empty string 为何?这是因为shell将$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" ...
is readable-s FILE_NAM # TrueifFILE_NAM existsandisnotempty-w FILE_NAM # TrueifFILE_NAM has write permission-x FILE_NAM # TrueifFILE_NAM is executable#字符串测试操作-z STRING # TrueifSTRING is empty-n STRING # TrueifSTRING isnotemptySTRING1...
How To Bash Shell Find Out If a Variable Is Empty Or Not #!/bin/bashJAIL="/nginx"HINT=""# Do three possibilities for $JAIL ##for i in 1 2 3 docase $i in1) JAIL="/nginx/jail"; HINT="value set";;2) JAIL=""; HINT="value set to empty string";;3) unset JAIL; HINT="...
# Check if the string is empty if [ -z "$input_str" ]; then echo "The string is empty" else echo "The string is not empty" fi Output: The string is empty Explanation: In the exercise above, The variable 'input_str' is defined as an 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...