Implement Exists Builtin Command (#504)

examples/exists.ion

@@ -0,0 +1,96 @@
+# Same tests as in src/builtins/exists.rs:test_evaluate_arguments()
+# TODO: find a better way than to write "echo $?" between each test cases
+exists
+echo $?
+exists foo bar
+echo $?
+
+exists --help
+echo $?
+exists --help unused params
+echo $?
+
+
+exists ""
+echo $?
+exists string
+echo $?
+exists "string with spaces"
+echo $?
+exists "-startswithdash"
+echo $?
+
+
+exists -a
+echo $?
+let emptyarray = []
+echo @emptyarray
+exists -a emptyarray
+echo $?
+let array = [ "element" ]
+echo @array
+exists -a array
+echo $?
+exists -a array
+echo $?
+
+
+exists -b
+echo $?
+let OLDPATH = $PATH
+let PATH = testing/
+echo "PATH = $PATH"
+ls -1 $PATH
+exists -b executable_file
+echo $?
+exists -b empty_file
+echo $?
+exists -b file_does_not_exist
+echo $?
+let PATH = $OLDPATH
+echo "Reset PATH to old path"
+
+exists -d
+echo $?
+exists -d testing/
+echo $?
+exists -d testing/empty_file
+echo $?
+exists -d does/not/exist
+echo $?
+
+
+exists -f
+echo $?
+exists -f testing/
+echo $?
+exists -f testing/empty_file
+echo $?
+exists -f does-not-exist
+echo $?
+
+fn testFunc a
+  echo $a
+end
+exists --fn testFunc
+echo $?
+
+exists -s
+echo $?
+let emptyvar = ""
+echo "emptyvar = $emptyvar"
+exists -s emptyvar
+echo $?
+let testvar = "foobar"
+echo "testvar = $testvar"
+exists -s testvar
+echo $?
+drop testvar
+echo "testvar = $testvar"
+exists -s testvar
+echo $?
+
+exists --foo
+echo $?
+exists -x
+echo $?

examples/exists.out

@@ -0,0 +1,152 @@
+1
+0
+NAME
+    exists - check whether items exist
+
+SYNOPSIS
+    exists [EXPRESSION]
+
+DESCRIPTION
+    Checks whether the given item exists and returns an exit status of 0 if it does, else 1.
+
+OPTIONS
+    -a ARRAY
+        array var is not empty
+
+    -b BINARY
+        binary is in PATH
+
+    -d PATH
+        path is a directory
+        This is the same as test -d
+
+    -f PATH
+        path is a file
+        This is the same as test -f
+
+    --fn FUNCTION
+        function is defined
+
+    -s STRING
+        string var is not empty
+
+    STRING
+        string is not empty
+        This is the same as test -n
+
+EXAMPLES
+    Test if the file exists:
+        exists -f FILE && echo "The FILE exists" || echo "The FILE does not exist"
+
+    Test if some-command exists in the path and is executable:
+        exists -b some-command && echo "some-command exists" || echo "some-command does not exist"
+
+    Test if variable exists AND is not empty
+        exists -s myVar && echo "myVar exists: $myVar" || echo "myVar does not exist or is empty"
+        NOTE: Don't use the '$' sigil, but only the name of the variable to check
+
+    Test if array exists and is not empty
+        exists -a myArr && echo "myArr exists: @myArr" || echo "myArr does not exist or is empty"
+        NOTE: Don't use the '@' sigil, but only the name of the array to check
+
+    Test if a function named 'myFunc' exists
+        exists --fn myFunc && myFunc || echo "No function with name myFunc found"
+
+AUTHOR
+    Written by Fabian Würfl.
+    Heavily based on implementation of the test builtin, which was written by Michael Murph.
+0
+NAME
+    exists - check whether items exist
+
+SYNOPSIS
+    exists [EXPRESSION]
+
+DESCRIPTION
+    Checks whether the given item exists and returns an exit status of 0 if it does, else 1.
+
+OPTIONS
+    -a ARRAY
+        array var is not empty
+
+    -b BINARY
+        binary is in PATH
+
+    -d PATH
+        path is a directory
+        This is the same as test -d
+
+    -f PATH
+        path is a file
+        This is the same as test -f
+
+    --fn FUNCTION
+        function is defined
+
+    -s STRING
+        string var is not empty
+
+    STRING
+        string is not empty
+        This is the same as test -n
+
+EXAMPLES
+    Test if the file exists:
+        exists -f FILE && echo "The FILE exists" || echo "The FILE does not exist"
+
+    Test if some-command exists in the path and is executable:
+        exists -b some-command && echo "some-command exists" || echo "some-command does not exist"
+
+    Test if variable exists AND is not empty
+        exists -s myVar && echo "myVar exists: $myVar" || echo "myVar does not exist or is empty"
+        NOTE: Don't use the '$' sigil, but only the name of the variable to check
+
+    Test if array exists and is not empty
+        exists -a myArr && echo "myArr exists: @myArr" || echo "myArr does not exist or is empty"
+        NOTE: Don't use the '@' sigil, but only the name of the array to check
+
+    Test if a function named 'myFunc' exists
+        exists --fn myFunc && myFunc || echo "No function with name myFunc found"
+
+AUTHOR
+    Written by Fabian Würfl.
+    Heavily based on implementation of the test builtin, which was written by Michael Murph.
+0
+1
+0
+0
+0
+0
+
+1
+element
+0
+0
+0
+PATH = testing/
+empty_file
+executable_file
+file_with_text
+symlink
+0
+1
+1
+Reset PATH to old path
+0
+0
+1
+1
+0
+1
+0
+1
+0
+0
+emptyvar = 
+1
+testvar = foobar
+0
+testvar = 
+1
+0
+0

examples/glob.out

@@ -5,7 +5,7 @@ Cargo.toml
 Cargo.lock Cargo.toml
 Cargo.toml
 Cargo.toml
-examples/else_if.ion examples/fail.ion examples/fibonacci.ion examples/fn.ion examples/for.ion examples/function_piping.ion
+examples/else_if.ion examples/exists.ion examples/fail.ion examples/fibonacci.ion examples/fn.ion examples/for.ion examples/function_piping.ion
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