Differences

This shows you the differences between two versions of the page.

--- linux:bash [2022/02/28 14:15] – [Arguments] mh
+++ linux:bash [2026/01/11 11:57] (current) – [Control Operators] mh
@@ Line 113: / Line 113: @@
 ----
+=== 2>/dev/null || true ===
+<code bash>
+$ something 2>/dev/null || true
+</code>
+This means:
+Try something, but if it errors (exit code ≠ 0):
+  * silence the error message (send to ''/dev/null'')
+  * immediately run ''true'' ( || operator passes along to second part)
+  * Overall ''exit'' status becomes success (exit code = 0)
+In plain English:
+“Try to do the cleanup.
+If there’s nothing to clean, that’s fine. Move on.”
+This pattern is **not appropriate** when:
+  * Failure is meaningful
+  * You want to be alerted
+  * Data loss is possible
+  * You are debugging
+In those cases, we want ''stderr'' and non-zero exits.
+So this is not about hiding problems.
+It’s about acknowledging expected non-problems.
+----
+=== && AND Operator ===
+This control operator tells bash to run a second command **only if the first command before it succeeded**.
+If the first command fails, the second command is entirely skipped.
+**Example**
+<code bash>
+$ rm hello.txt && echo "Deleted file."
+rm: cannot remove 'hello.txt': No such file or directory
+</code>
+Because the file did not exist, the ''echo'' command was not run.
 ===== Arguments =====
@@ Line 203: / Line 247: @@
 There can be **no whitespace** around the = operator !
-If a whitespace is required in the variable, use '' quotes to create a literal
+If a whitespace is required in the variable, use 'single quotes' to create a literal
 </WRAP>
@@ Line 343: / Line 387: @@
 As a result, both file descriptors are connected to the same stream.
+Be careful not to write something like ''$ ls -l a b >myfiles.ls 2>myfiles.ls'' as due to the way streams are handled they will most likely end up mixing up and garbling the file 'myfiles.ls'
 </WRAP>