If you are interested in finding out whether a variable has been declared regardless of its value, then using the in operator is the safest way to go. Consider this example:
// global scope\nvar theFu; // theFu has been declared, but its value is undefined\ntypeof theFu; // "undefined"\n But this may not be the intended result for some cases, since the variable or property was declared but just not initialized. Use the in operator for a more robust check.
"theFu" in window; // true\n"theFoo" in window; // false\n If you are interested in knowing whether the variable hasn\'t been declared or has the value undefined, then use the typeof operator, which is guaranteed to return a string:
if (typeof myVar !== 'undefined')\n Direct comparisons against undefined are troublesome as undefined can be overwritten.
window.undefined = "foo";\n"foo" == undefined // true\n As @CMS pointed out, this has been patched in ECMAScript 5th ed., and undefined is non-writable.
if (window.myVar) will also include these falsy values, so it\'s not very robust:
\nfalse\n0\n\"\"\nNaN\nnull\nundefined\n\n\n
Thanks to @CMS for pointing out that your third case - if (myVariable) can also throw an error in two cases. The first is when the variable hasn\'t been defined which throws a ReferenceError.
// abc was never declared.\nif (abc) {\n // ReferenceError: abc is not defined\n} \nThe other case is when the variable has been defined, but has a getter function which throws an error when invoked. For example,
\n\n// or it's a property that can throw an error\nObject.defineProperty(window, "myVariable", { \n get: function() { throw new Error("W00t?"); }, \n set: undefined \n});\nif (myVariable) {\n // Error: W00t?\n}\n--Anurag
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\nconvert input.jpg -rotate <angle in degrees> out.jpg\n\n
To rotate 90 degrees clockwise:
\nconvert input.jpg -rotate 90 out.jpg\nTo save the file with the same name:
\nconvert file.jpg -rotate 90 file.jpg\nTo rotate all files:
\nfor photo in *.jpg ; do convert $photo -rotate 90 $photo ; done\n Alternatively, you can also use the mogrify command line tools (the best tool) recommended by @don-crissti:
mogrify -rotate 90 *.jpg\n--GAD3R
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