Differences

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--- bash:brackets [2021/01/09 13:53] – [Comparisons between [ and [[] peter
+++ bash:brackets [2021/01/09 13:59] (current) – [Rule of Thumb] peter
@@ Line 145: / Line 145: @@
 |RegularExpression matching|<nowiki>=~</nowiki>|(not available)|<nowiki>[[ $(date) =~ ^Fri\ ...\ 13 ]] && echo "It's Friday the 13th!"</nowiki>|
-  * (*) This is an extension to the POSIX standard; some shells may have it, others may not.
+  * **<nowiki>(*)</nowiki>** This is an extension to the POSIX standard; some shells may have it, others may not.
-  * (**) The -a and -o operators, and ( ... ) grouping, are defined by POSIX but only for strictly limited cases, and are marked as deprecated. Use of these operators is discouraged; you should use multiple <nowiki>[</nowiki> commands instead:
+  * **<nowiki>(**)</nowiki>** The -a and -o operators, and ( ... ) grouping, are defined by POSIX but only for strictly limited cases, and are marked as deprecated.
-    *  if [ "$a" = a ] && [ "$b" = b ]; then ...
+    * Use of these operators is discouraged; you should use multiple <nowiki>[</nowiki> commands instead:
-    *  if [ "$a" = a ] || { [ "$b" = b ] && [ "$c" = c ];}; then ...
+      *  if [ "$a" = a ] && [ "$b" = b ]; then ...
+      *  if [ "$a" = a ] || { [ "$b" = b ] && [ "$c" = c ];}; then ...
 ----
@@ Line 197: / Line 198: @@
 </code>
-As of bash 4.1, string comparisons using < or > respect the current locale when done in <nowiki>[[</nowiki>, but not in <nowiki>[</nowiki> or test. In fact, <nowiki>[</nowiki> and test have never used locale collating order even though past man pages said they did. Bash versions prior to 4.1 do not use locale collating order for <nowiki>[[</nowiki> either.
+As of bash 4.1, string comparisons using < or > respect the current locale when done in **<nowiki>[[</nowiki>**, but not in **<nowiki>[</nowiki>** or test.
+In fact, **<nowiki>[</nowiki>** and test have never used locale collating order even though past man pages said they did.
+Bash versions prior to 4.1 do not use locale collating order for **<nowiki>[[</nowiki>** either.
 ----
@@ Line 203: / Line 208: @@
 ===== Rule of Thumb =====
-As a rule of thumb, [[ is used for strings and files.
+As a rule of thumb, **[[** is used for strings and files.
 If you want to compare numbers, use an ArithmeticExpression, e.g.
@@ Line 213: / Line 218: @@
 </code>
-When should the new test command <nowiki>[[</nowiki> be used, and when the old one <nowiki>[</nowiki>?  If portability/conformance to POSIX or the Bourne Shell is a concern, the old syntax should be used.  If on the other hand the script requires BASH, Zsh, or KornShell, the new syntax is usually more flexible, but not necessarily backwards compatible.
+When should the new test command <nowiki>[[</nowiki> be used, and when the old one <nowiki>[</nowiki>?
+  * If portability/conformance to POSIX or the Bourne Shell is a concern, the old syntax should be used.
+  * If on the other hand the script requires BASH, Zsh, or KornShell, the new syntax is usually more flexible, but not necessarily backwards compatible.
-For reasons explained in the theory section below, any problem with an operator used with <nowiki>[[</nowiki> is an unhandleable parse-time error that will cause bash to terminate, even if the command is never evaluated.
+<WRAP info>
+**NOTE:**  Any problem with an operator used with **<nowiki>[[</nowiki>** resulting in an unhandleable parse-time error will cause bash to terminate, even if the command is never evaluated.
+</WRAP>