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syntax:ccmd:case [2013/02/01 13:27] ormaaj [Examples] A practical example to show off my video power function. |
syntax:ccmd:case [2017/02/08 15:04] (current) fgrose [Description] describe the separation of PATTERNn from surroundings |
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| ===== Description ===== | ===== Description ===== | ||
| - | 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''). | + | 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''). Every ''<PATTERNn>'' is separated from it's associated ''<LISTn>'' by a '')'', and is optionally preceded by a ''(''. |
| - | :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: | 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: | ||
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| This is similar to the behavior of the [[syntax:ccmd:conditional_expression | conditional expression command ("new test command")]] (also no word splitting for expansions). | 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. | Multiple ''|''-delimited patterns can be specified for a single block. This is a POSIX-compatable equivalent to the ''@(pattern-list)'' extglob construct. | ||