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--- syntax:ccmd:case [2012/07/31 10:56]
ormaaj [Portability considerations]
+++ syntax:ccmd:case [2013/04/14 12:33]
thebonsai Don't tread version 4 special - it has been around for a long time now
@@ Line 15: / Line 15: @@
 The ''case''-statement can execute commands based on a [[syntax:pattern | pattern matching]] decision. The word ''<WORD>'' is matched against every pattern ''<PATTERNn>'' and on a match, the associated [[syntax:basicgrammar#lists | list]] ''<LISTn>'' is executed. Every commandlist is terminated by ''<nowiki>;;</nowiki>'', this rule is optional for the very last commandlist (i.e. you can omit the ''<nowiki>;;</nowiki>'' before the ''esac'').
-:V4: Bash 4 introduces two new action terminators. The classic behavior using '';;'' is to execute only the list associated with the first matching pattern, then break out of the ''case'' block. The '';&'' terminator causes ''case'' to also execute the next block without testing its pattern. The '';;&'' operator is like '';;'', except the case statement doesn't terminate after executing the associated list - Bash just continues testing the next pattern as though the previous pattern didn't match. Using these terminators, a ''case'' statement can be configured to test against all patterns, or to share code between blocks, for example.
+Bash 4 introduces two new action terminators. The classic behavior using '';;'' is to execute only the list associated with the first matching pattern, then break out of the ''case'' block. The '';&'' terminator causes ''case'' to also execute the next block without testing its pattern. The '';;&'' operator is like '';;'', except the case statement doesn't terminate after executing the associated list - Bash just continues testing the next pattern as though the previous pattern didn't match. Using these terminators, a ''case'' statement can be configured to test against all patterns, or to share code between blocks, for example.
 The word ''<WORD>'' is expanded using //tilde//, //parameter// and //variable expansion//; //arithmetic//, //command// and //process substitution//; and //quote removal//. **No word splitting, brace, or pathname expansion is done**, which means you can leave expansions unquoted without problems:
@@ Line 27: / Line 27: @@
 This is similar to the behavior of the [[syntax:ccmd:conditional_expression | conditional expression command ("new test command")]] (also no word splitting for expansions).
-Unlike the C-case-statement, only the matching list and nothing else is executed. If more patterns match the word, only the first match is taken. (**Note** the comment about :V4: Bash v4 changes above.)
+Unlike the C-case-statement, only the matching list and nothing else is executed. If more patterns match the word, only the first match is taken. (**Note** the comment about Bash v4 changes above.)
 Multiple ''|''-delimited patterns can be specified for a single block. This is a POSIX-compatable equivalent to the ''@(pattern-list)'' extglob construct.
@@ Line 36: / Line 36: @@
 Another one of my stupid examples...
 <code>
-read -rp "Which fruit do you like most? " fruit
+printf '%s ' 'Which fruit do you like most?'
+read -${BASH_VERSION+e}r fruit
-case "$fruit" in
+case $fruit in
-  apple)              echo "Mmmmh... I like those!"
+    apple)
-                      ;;
+        echo 'Mmmmh... I like those!'
-  banana)             echo "Hm, a bit awry, no?"
+        ;;
-                      ;;
+    banana)
-  orange|tangerine)   echo "Eeeks! I don't like those!"
+        echo 'Hm, a bit awry, no?'
-                      echo "Go away!"
+        ;;
-                      exit 1
+    orange|tangerine)
-                      ;;
+        echo $'Eeeks! I don\'t like those!\nGo away!'
-  *)                  echo "Unknown fruit - sure it isn't toxic?"
+        exit 1
-                      ;;
+        ;;
+    *)
+        echo "Unknown fruit - sure it isn't toxic?"
 esac
+</code>
+Here's a practical example showing a common pattern involving a ''case'' statement. If the first argument is one of a valid set of alternatives, then perform some sysfs operations under Linux to control a video card's power profile. Otherwise, show a usage synopsis, and print the current power profile and GPU temperature.
+<code bash>
+# Set radeon power management
+function clk {
+	typeset base=/sys/class/drm/card0/device
+	[[ -r ${base}/hwmon/hwmon0/temp1_input && -r ${base}/power_profile ]] || return 1
+	case $1 in
+		low|high|default)
+			printf '%s\n' "temp: $(<${base}/hwmon/hwmon0/temp1_input)C" "old profile: $(<${base}/power_profile)"
+			echo "$1" >${base}/power_profile
+			echo "new profile: $(<${base}/power_profile)"
+			;;
+		*)
+			echo "Usage: $FUNCNAME [ low | high | default ]"
+			printf '%s\n' "temp: $(<${base}/hwmon/hwmon0/temp1_input)C" "current profile: $(<${base}/power_profile)"
+	esac
+}
 </code>
 A template for experiments with ''case'' logic, showing shared code between blocks using '';&'', and the non-short-circuiting '';;&'' operator:
-<code>
+<code bash>
 #!/usr/bin/env bash