[Linux] How to find all files containing specific text on Linux?

grep -rnw '/path/to/somewhere/' -e 'pattern'

• -r or -R is recursive,
• -n is line number, and
• -w stands for match the whole word.
• -l (lower-case L) can be added to just give the file name of matching files.

P.S. example: to find "if ["

grep -rnw '/path/to/somewhere/' -e 'if \['




[Linux] Create encrypted (password protected) zip/upzip file

 - zip 

This will prompt for a password:

zip --encrypt file.zip files

This is more insecure, as the password is entered/shown as plain text:

zip --password (password) file.zip files

Warning, the standard zip encryption is very weak and is easily cracked.

- unzip 

unzip -P (password) file.zip

[Linux] How can I get what my main function has returned

Most shells store the exit code of the previous run command in $? so you can store or display it.

$ ./a.out
$ echo $?     # note - after this command $? contains the exit code of echo!

or

$ ./a.out
$ exit_code=$?    # save the exit code in another shell variable.

[Linux] Checking if a directory exists in Unix (system call)

#include <sys/stat.h>

struct stat sb;

if (stat(pathname, &sb) == 0 && S_ISDIR(sb.st_mode))
{
    ...it is a directory...
}

[Xcode] Fixed: Build error that it import Objective-C codes in the .cpp?

Build error: (NSObjCRuntime.h & NSObject)

/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/System/Library/Frameworks/Foundation.framework/Headers/NSObjCRuntime.h:371:1: Expected unqualified-id

/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/System/Library/Frameworks/Foundation.framework/Headers/NSObjCRuntime.h:373:19: Unknown type name 'NSString'
...

/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/usr/include/objc/NSObject.h:11:1: Expected unqualified-id
...


[Solution]
rename extension name from .cpp into .mm

[Xcode] Fixed: _CMAudioFormatDescriptionGetStreamBasicDescription", referenced from: -[captureNSObject init] in captureNSObject.o

I have a project to build some code,  and then it has error in the follow:

Undefined symbols for architecture x86_64:

  "_CMAudioFormatDescriptionGetStreamBasicDescription", referenced from:

      -[captureNSObject init] in captureNSObject.o

  "_CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer", referenced from:

      -[captureNSObject captureOutput:didOutputSampleBuffer:fromConnection:] in captureNSObject.o

  "_CMSampleBufferGetNumSamples", referenced from:

      -[captureNSObject captureOutput:didOutputSampleBuffer:fromConnection:] in captureNSObject.o

ld: symbol(s) not found for architecture x86_64

clang: error: linker command failed with exit code 1 (use -v to see invocation)

[Solution]

Add CoreMedia.framework into "Linked Frameworks and Libraries".

[Xcode] Enable/disable a button

@property (retain, nonatomic) IBOutlet UIButton *btnButton;

enable/disable like this in .m file:

btnButton.enabled = NO; // disable button
btnButton.enabled = YES; // enable button