we have initialized a file variable “F” holding a path to a file “new.txt” as “/home/linux/new.txt”. The “if-then” statement of bash has been utilized here to check if the file “new.txt” exists or not. The “if” clause is started with the keyword “test” followed...
3. By comparing a variable to an empty string As the name suggests, in this method, I will be comparing the variable to an empty string using the[]operator. Here's the simple script: #!/bin/bash if [ "$variable" = "" ]; then echo "Variable is empty." else echo "Variable is ...
在Bash Shell中,可以使用复合条件来在一个if语句中检查多个条件。复合条件主要有两种形式:逻辑与(&&)和逻辑或(||)。 1. 逻辑与(&&): - 概念:逻辑与用于同时检查多个条件...
Checking If Variable Is Empty in Bash There are multiple ways to check if a variable is empty or not. Before moving towards those methods, knowing when a variable is called empty is necessary. In Bash, a variable is called empty if: A variable is declared without assigning any value to ...
Example Bash script: if getent passwd "$username" >/dev/null; then echo "User $username exists" else echo "User $username does not exist" fi Replace the variable$usernamewith the name of the user you want to check. If you want to check if a username does not exist, you can negate ...
if getent group "$groupname" >/dev/null; then echo "Group $groupname exists" fi Replace$groupnamewith the name of the group you want to check. If you like to check if the group does not exist (e.g. because you like to create it in this case, then you can negate the command us...
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
# Check if file is empty if["$file_size"-gt"$size_threshold"] then echo"File exists and is not empty" else echo"File exists but is empty" fi else echo"File does not exist" fi In this bash script example, we first set the filename, the size_threshold variable and then check if ...
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# Check requirementsforcmdincurl jshonexpr;doif! `which${cmd}1>/dev/null`;thenecho"UNKNOWN: ${cmd} does not exist, please check if command exists and PATH is correct"exit ${STATE_UNKNOWN}fidone### # Checkforpeoplewhoneed help - aren't we all nice ;-)if["${1}"="--help"-o"...