The-zoperator returnstrueif a string variable is null or empty. How the use the-zBash Operator 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 "...
当然,无法在bash中转换null和false情况,因此省略它们. function empty { local var="$1" # Return true if: # 1. var is a null string ("" as empty string) # 2. a non set variable is passed # 3. a declared variable or array but without a value is passed # 4. an empty array is pa...
# Return true if: # 1. var is a null string ("" as empty string) # 2. a non set variable is passed # 3. a declared variable or array but without a value is passed # 4. an empty array is passed if test -z"$var" then [[ $( echo"1" ) ]] return # Return true if var...
if ps ax | grep oracle > /dev/null 2>&1 ; then ... fi 首先, 这是合法的, 它的目的是想知道进程列表中有没有与oracle相关的东西, 当然, 如果你够牛, 就能看出这种做法有另外的问题. 但这不是我想说的重点. 我想说的是, 你前面被教导的这种if 语句的语法模型, 如何解释这个, [ 与 ] 又不...
ZSH_THEME="pure" ZSH_THEME="ys" # Set list of themes to pick from when loading at random # Setting this variable when ZSH_THEME=random will cause zsh to load # a theme from this variable instead of looking in ~/.oh-my-zsh/themes/ # If set to an empty array, this variable will...
How to check if a variable exists or is “null”? How to check if a file exists? How to check if a directory exists? How to check if a command succeeds or failed? How to do string comparison and check if a string equals to a value? How to check if a string is in an array?
# Create the variable name. $ var="world" $ ref="hello_$var" # Print the value of the variable name stored in 'hello_$var'. $ printf '%s\n' "${!ref}" value 1. 2. 3. 4. 5. 6. 7. 8. 9. 或者,在bash4.3+上:
Bash behaves as if the following command were exe- cuted: if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi but the value of the PATH variable is not used to search for the file name. If bash is invoked with the name sh, it tries to mimic the startup behavior of historical ...
Then, the if statement checks if the $count variable is zero. If the $count variable is zero, the grep output was empty, passed to the wc-1 because the pattern was not matched. The script then outputs the message No match found. to the console using the echo command. That’s all ab...
echo ${Variable/Some/A} # 会把 Variable 中首次出现的 "some" 替换成 “A”。 # 变量的截取 Length=7 echo ${Variable:0:Length} # 这样会仅返回变量值的前7个字符 # 变量的默认值 echo ${Foo:-"DefaultValueIfFooIsMissingOrEmpty"} #对 null (Foo=) 和空串 (Foo="") 起作用; 零(Foo=0)时...