if/else test equivalents for case control statement in bash
if/else test equivalents for case control statement in bash
I am writing a script in bash to easily loop some software, and depending on the inputs select a different strategy to use for a particular run. For example whether or not to run on all the files in a directory or just a subset, and whether files are paired or independent. (I'm working with fastq files if you an tell)
Usually I prefer to write case control statement whenever I have 3 or more options because I find it is easier to interpret and maintain. However I want to be able to test if certain files exist similar to when if/else statements in bash do if [ -e $foo ]; then etc That got me wondering if case control statements have any equivalent test options to if/else statements example
if [ -e $foo ]; then etc
More specifically I want to know if its possible to test for the existence of a file with a case statement
1 Answer
1
if doesn't have any test options; the test command (also spelled [) does. if and case do two separate things. case compares a single value to a number of patterns to see which matches. if and elif checks the exit status of a command. It just happens that test/[ is far and away the most command command used with an if statement.
if
test
[
if
case
case
if
elif
test
[
if
Each test like -e, -d, etc, corresponds to a call to a system call named stat which returns far more information than any one test actually uses; that information is just discarded. You could run an external program wrapper around stat (also called stat) yourself manually, then pattern match on its output with a case statement. That is a little less efficient, since it involves running an external program just to access the system call. However, the bash distribution does come with a stat built-in that you could to compile and enable yourself to mitigate that problem.
-e
-d
stat
stat
stat
case
bash
stat
(The change log for bash 5 mentions a new loadable builtin for stat—among other commands—, but it doesn't seem any different than the one that I though has been available for a while.)
bash
stat
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