SWIFT

Swift 4.2

textfield.addTarget(self, action: #selector(ViewController.textFieldDidChange(_:)), for: .editingChanged)
and

@objc func textFieldDidChange(_ textField: UITextField) {

}
SWIFT 3 & swift 4.1

textField.addTarget(self, action: #selector(ViewController.textFieldDidChange(_:)), for: .editingChanged)
and

func textFieldDidChange(_ textField: UITextField) {

}
SWIFT 2.2

textField.addTarget(self, action: #selector(ViewController.textFieldDidChange(_:)), forControlEvents: UIControlEvents.EditingChanged)
and

func textFieldDidChange(textField: UITextField) {
//your code
}
OBJECTIVE-C

[textField addTarget:self action:@selector(textFieldDidChange:) forControlEvents:UIControlEventEditingChanged];
and textFieldDidChange method is

-(void)textFieldDidChange :(UITextField *) textField{
//your code
}

I had this same error, but I had already checked "Automatically manage signing".

The solution was to uncheck it, then check it again and reselect the Team. Xcode then fixed whatever was causing the issue on its own.

In addition to Nick's answer about Xcode 4.2, you may also need to review your info.plist file. It seems as if new projects started in Xcode 4.2 by default specify 'armv7' in the 'Required Device Capabilities'. You'll need to remove this if wanting to support devices that run armv6 (e.g. the iPhone 3G).
Delete armv7 from the 'Required device capabilities' in yourProjectName-Info.plist

Objective-C:
***
UIView *bgColorView = [[UIView alloc] init];
bgColorView.backgroundColor = [UIColor redColor];
[cell setSelectedBackgroundView:bgColorView];
***
Swift:
***
let bgColorView = UIView()
bgColorView.backgroundColor = UIColor.red
cell.selectedBackgroundView = bgColorView
***

It forces applications to use the default language for output:
***
$ LC_ALL=es_ES man
¿Qué página de manual desea?

$ LC_ALL=C man
What manual page do you want?
***
and forces sorting to be byte-wise:
***
$ LC_ALL=en_US sort <<< $'a\nb\nA\nB'
a
A
b
B

$ LC_ALL=C sort <<< $'a\nb\nA\nB'
A
B
a
b
***

There is a vi available on every unix system (or almost), however you can't say this about any other editor. This is the #1 reason, imo, to learn and familiarize yourself with vi (please note 'vi' not 'vim'). I've never seen Emacs be available in a default install.

I'm not saying don't use Emacs or this is the only reason to use Vim, but when you want to be able to use Unix systems that aren't yours... vi is part of the universal language.

One simple use case for using dirs stack what you cannot do by just cd is:

pushd . adds current directory XX to dirs stack. Afterwards, you can move around using cd, and to return to XX you just do popd regardless of how "far away" are you in the directory tree (can jump over multiple levels, sideways etc). Especially useful in bash scripts.

One of the following 2 should work:
***
$ nohup redshift &
***
or
***
$ redshift &
$ disown
***
See the following for a bit more information on how this works:

man nohup

help disown

The self maintenance method is to vacuum the logs by size or time.

Retain only the past two days:
***
journalctl --vacuum-time=2d
***
Retain only the past 500 MB:
***
journalctl --vacuum-size=500M
***

bash and zsh have an array variable that holds the exit status of each element (command) of the last pipeline executed by the shell.

If you are using bash, the array is called PIPESTATUS (case matters!) and the array indicies start at zero:
***
$ false | true
$ echo "${PIPESTATUS[0]} ${PIPESTATUS[1]}"
1 0
***
If you are using zsh, the array is called pipestatus (case matters!) and the array indices start at one:
***
$ false | true
$ echo "${pipestatus[1]} ${pipestatus[2]}"
1 0
***
To combine them within a function in a manner that doesn't lose the values:
***
$ false | true
$ retval_bash="${PIPESTATUS[0]}" retval_zsh="${pipestatus[1]}" retval_final=$?
$ echo $retval_bash $retval_zsh $retval_final
1 0
***
Run the above in bash or zsh and you'll get the same results; only one of retval_bash and retval_zsh will be set. The other will be blank. This would allow a function to end with return $retval_bash $retval_zsh (note the lack of quotes!).

The main differences are:

wget's major strong side compared to curl is its ability to download recursively.
wget is command line only. There's no lib or anything, but curl's features are powered by libcurl.
curl supports FTP, FTPS, HTTP, HTTPS, SCP, SFTP, TFTP, TELNET, DICT, LDAP, LDAPS, FILE, POP3, IMAP, SMTP, RTMP and RTSP. wget supports HTTP, HTTPS and FTP.
curl builds and runs on more platforms than wget.
wget is released under a free software copyleft license (the GNU GPL). curl is released under a free software permissive license (a MIT derivate).
curl offers upload and sending capabilities. wget only offers plain HTTP POST support.

You can specify a slash at the end to match only directories:
***
for d in */ ; do
echo "$d"
done
***