Use the if-else statement with the -v option to check if an environment variable is set in bash. The echo command in the if block will be executed if the will
$ unset x $ showvar $x is not set $ x=3 $ showvar $x is not set $ export x $ showvar $x = 3 $ x= ## in bash, reassignment doesn't remove a variable from the environment $ showvar $x is set but empty 注意 showvar不是一个 bash 命令,而是一个如清单 5-1 所示的脚本,...
而if [ ! -z err]||[!−eapk ]; then 没问题; 整数比较 : -eq 等于,如:if [ "a"−eq"b" ] -ne 不等于,如:if [ "a"−ne"b" ] -gt 大于,如:if [ "a"−gt"b" ] -ge 大于等于,如:if [ "a"−ge"b" ] -lt 小于,如:if [ "a"−lt"b" ] -le 小于等于,如:if...
You can assign data to a variable using the equals sign (=). The data you store in a variable can either be a string or a number. Let’s create a variable now on the command line: chapter_number=5 The variable name is on the left hand side of the equals sign, and the data whic...
The operator return an exit code 0 (True) if the strings match the regular expression regex. The $BASH_REMATCH environment variable is a read-only Bash Array containing the values matched by the extended regular expression at the right side of the =~ binary operator in a double-bracket [[...
if [[ ! -f $FILE ]] then echo "The file ${FILE} does not exist!" fi done Save your script and add the “bin” folder you just created to your PATH environment variable. $ export PATH="~/bin:$PATH" $ printenv PATH ~/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin...
Method 1: Theif [ -d $directory ]Command ([Operator) Theif [ -d $directory ]command can be used to check for the existence of a directory. If the specified directory exists, the command will return an exit status of0(true). If the directory does not exist, the command will return ...
The proper way to handle errors is to check if the program finished successfully or not, using return codes. It sounds obvious but return codes, an integer number stored in bash$?or$!variable, have sometimes a broader meaning. Thebash man pagetells you: ...
When bash is started non-interactively, to run a shell script, for example, it looks for the variable BASH_ENV in the environment, expands its value if it appears there, and uses the expanded value as the name of a file to read and execute. Bash behaves as if the following command ...
Associative arrays first appeared in Bash version 4. Check the Bash version on your system using the following environment variable: echo $BASH_VERSION TheBASH_VERSIONvariable stores the currently running Bash shell version. If the command does not print any output, Bash is either not running on...