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--- ops102:bash_scripting_1 [2025/03/08 02:55] – [Setting a Variable] chris
+++ ops102:bash_scripting_1 [2025/03/11 15:11] (current) – chris
@@ Line 38: / Line 38: @@
   The current date and time is:
   Sat Mar  6 12:03:32 EST 2038
+===== Comments =====
+A comment in a bash script starts with a sharp symbol (#) and is ignored by the shell interpreter:
+<code># test script #1
+# written by Jason Bourne</code>
+A comment may also be just one portion of a line:
+<code>cd - # change to the user's previous working directory</code>
+Note that a shbang line is a comment from the point of view of the shell interpreter -- it's there for the kernel to use, not the shell!
 ===== Variables =====
@@ Line 55: / Line 68: @@
 Unlike some computer languages such as C, variables do not need to be declared. Variables are not typed -- they may be used as strings, integers, or decimal values.
+Note that there must not be a space on either side of the equal sign.
 ==== Accessing a Variable ====
@@ Line 103: / Line 117: @@
   Hello $B
-You should always double-quote variables that may contain a space in their value when using them as command arguments.
+You should always double-quote variables that may contain a space in their value when using them as command arguments. This is especially true for filenames -- you never know when a user is going to put a space in a filename! Many scripts work find with opaque filenames (those containing no whitespace) but fail with non-opaque names.
+Here is an example -- the difference between the first ''ls'' statement (which does not double-quote the variable) and the second ''ls'' statement (where the variable expansion is double-quoted):
-This is especially true for filenames -- you never know when a user is going to put a space in a filename! Many scripts work find with opaque filenames (those containing no whitespace) but fail with non-opaque names.
+  $ touch "red maple"
+  $ FILE="red maple"
+  $ ls $FILE
+  ls: cannot access 'red': No such file or directory
+  ls: cannot access 'maple': No such file or directory
+  $ ls "$FILE"
+  'red maple'
 === Backslashes ===