![\"Bash](\"https:\/\/linuxadmin.io\/wp-content\/uploads\/2017\/07\/bash_scripting_introduction.png\")
<\/p>\n<\/p>\n
Essentially bash scripting is just linking commands together. You can perform many tasks consistently using predefined scripts allowing them to become repeatable and standardized. If you are looking for more information you can check out the bash man page<\/a>.<\/p>\n Each script should start with a \u201cshebang\u201d telling which environment to interpret the script, bash scripts start with<\/p>\n #!\/bin\/bash<\/p>\n In CentOS\/RHEL 7 , \/bin\/sh is symlinked to \/bin\/bash<\/p>\n To make a script execute, you can either call it via the interpreter<\/p>\n \/bin\/bash myscript.sh<\/p>\n Or change the permissions to make it executable<\/p>\n chmod ug+x myscript.sh<\/p>\n and then execute it directly<\/p>\n .\/myscript.sh<\/p>\n Test comparison operators are use to compare two pieces of information.<\/p>\n Are used to compare to strings together<\/p>\n $x = $y \u2013 if $x is equal to $y, this will be true<\/em> Integer tests are used to compare to integers together<\/p>\n $x -eq $y \u2013 if $x is equal to $y this will be true.<\/em> Test operators are used to test if a condition is true.<\/p>\n -d FILE \u2013 True if file is a directory.<\/em> To utilize the above test operators, you will need to use \u2018if\u2019 statements<\/p>\n To use a comparison:<\/p>\n if [ $x -eq $y ]; then To use a test operator:<\/p>\n if [ -d \/home ]; then Loops can be utilized to do the same task multiple times<\/p>\n for i in ; do The output will be<\/p>\n I have a apple These are done, while something is true perform the following task<\/p>\n i=0 The output will be:<\/p>\n i is currently at 0 You can use arguments to pass stored data into a script and store it as a variable. The first argument is stored as $1, the second argument is stored as $2 and so on.<\/p>\n if [ $1 -eq $2 ]; then The output would be<\/p>\n .\/compare_arguments 3 5 .\/compare_arguments 4 4 You can also require a certain number of arguments be entered by using $#<\/p>\n if [ $# -ne 2 ]; then Which indicates if the number of required arguments is not 2, then exit.<\/p>\n Jul 16, 2017LinuxAdmin.io<\/p>\nBash Test Comparison Operators<\/h2>\n
String Tests:<\/h3>\n
\n$x != $y \u2013 if $x is not equal to $y, this will be true<\/em><\/p>\nInteger Tests:<\/h3>\n
\n$x -ne $y \u2013 if $x is not equal to $y, this will be true.<\/em>
\n$x -ge $y \u2013 if $x is greater than or equal to $y, this will be true.<\/em>
\n$x -gt $y \u2013 if $x is greater than $y, this will be true.<\/em>
\n$x -le $y -if $x is less than or equal to $y, this will be true.<\/em>
\n$x -lt $y \u2013 if $x is less then $y, this will be true.<\/em><\/p>\nBash Test Operators<\/h3>\n
\n-e FILE \u2013 True if file exists.<\/em>
\n-f FILE \u2013 True if exists and is a file.<\/em>
\n-r FILE \u2013 True if file exists and is readable.<\/em>
\n-w FILE \u2013 True if file exists and is granted write permissions.<\/em>
\n-x FILE \u2013 True if file exists and is granted execute permissions.<\/em><\/p>\nBash If Statements<\/h2>\n
\necho “x equals y”;
\nelse
\necho “x does not equal y”;
\nfi<\/p>\n
\necho “\/home exists”;
\nelse
\necho “\/home does not exist”;
\nfi<\/p>\nBash Loops<\/h2>\n
For Loops<\/h3>\n
\necho “I have a $”;
\ndone<\/p>\n
\nI have a orange
\nI have a watermelon<\/p>\nWhile Loops<\/h3>\n
\nwhile [ $i -le 5 ]
\ndo
\necho “i is currently at $”;
\n((i++))
\ndone<\/p>\n
\ni is currently at 1
\ni is currently at 2
\ni is currently at 3
\ni is currently at 4
\ni is currently at 5<\/p>\nBash Script Arguments<\/h2>\n
\necho “The arguments are equal”;
\nelse
\necho “The arguments are not equal”
\nfi<\/p>\n
\nThe arguments are not equal<\/p>\n
\nThe arguments are equal<\/p>\n
\necho “the number of required arguments is 2”;
\nexit;
\nfi<\/p>\n