When I enter text on stdin in an OS X Terminal, a single line is limited to 1024 characters. For example, cat > /dev/null beeps after I type (or paste) a line longer than this, and refuses to accept more characters. A problematic example is when I want to count characters from pasted text with cat | wc -c: the cat blocks at the first long line.

This seems to be a general problem with pasting to stdin. Can this observed stdin limitation of 1024 characters per line be removed or pushed to a higher limit?

I need this because I want to paste text that has lines longer than 1024 characters.

I could also use a "heredoc" << EOT and paste my long lines without any problem, but then the text appears in my shell history, which I don't want.

  • That's annoying. I guess the Heredoc approach is a tolerable work-around, since you can tell the shell to not add a command line that starts with a space. See Is there any way to keep a command from being added to your history? for details for various shells, including zsh. – PM 2Ring May 21 '15 at 13:16
  • This is a badly phrased question. In the Z shell the limit is not 1024 characters. You're actually talking about a limit that is not implemented by the Z Shell, nor in force when the Z shell is the program that is reading input from the terminal. In this case, it is cat that is doing the reading, and the Z shell isn't involved. This ground has been covered before, with cat, at unix.stackexchange.com/questions/131105 . – JdeBP May 21 '15 at 18:12
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    Call pbpaste instead of pasting. (That's on OSX; under X11, call xsel or xclip.) – Gilles 'SO- stop being evil' May 21 '15 at 23:17
  • @JdeBP My question was obviously not about zsh but about the cat command not working like I needed: I was giving details about my environment (zsh, OS X Terminal), in case they mattered. – Eric O Lebigot May 22 '15 at 2:49
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    @mikeserv Thank you for the ideas. The less - f /dev/tty does not work, for me, unfortunately. Another idea, though, for remote host pasting, is to uuencode first (so as to get short lines). – Eric O Lebigot May 22 '15 at 5:01

Probably a limit of the terminal device line discipline internal line editor buffer.

You should be able to enter long lines by pressing Ctrl+D in the middle of it (so the currently entered part be sent to cat and the line editor flushed), or by disabling that line editor altogether.

For instance, if using zsh:

STTY=-icanon cat > file

Note that then you can't use Backspace or any other editing capability. You'd also need to press Ctrl-C to stop cat.

With other shells:

s=$(stty -g); stty -icanon; cat > file

Followed by:

stty "$s"

Or just:

stty -icanon; cat > file
stty sane

Of course, things like

cat | wc -l


wc -l

won't work. Because Ctrl+C kills all the processes in the foreground process group.

You could do:

STTY=-icanon cat | (trap '' INT; wc -l)

Or as suggested by @mikeserv:

STTY='eol " "' wc -l

That way, the buffer will be flushed every time you enter space. You're still in canonical mode, so you can still edit words (as opposed to lines) and use Ctrl+D to signify EOF.


STTY='-icanon min 0 time 30' wc -l

EOF will come 3 seconds after you stop typing. Or:

STTY=-icanon sed -n '/^EOF$/q;p' | wc -l

And enter EOF (the 3 letters on a line on its own) to end the input.

As suggested by Gilles, where possible (as in generally not a telnet/ssh session for instance), use pbpaste instead of pasting. (That's on OSX; under X11, call xsel or xclip.):

pbpaste | wc -l

That will also avoid problems with some control characters (like ^C) that may be found in the copy-paste buffer.

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  • This does indeed allow me to paste long lines. However, it does not work for the general case of pasting to stdin: for example, STTY=-icanon cat | wc -c does not produce any result (I guess that the necessary Ctrl-C kills wc). – Eric O Lebigot May 22 '15 at 3:02
  • @EOL - the CTRL-C isn't necessary - use the eof char - CTRL-D by default. Actually, nevermind CTRL-D - but you can use CTRL-J to end the line. Alternatively - and probably not a great idea - set noflsh. If you use dd rather than cat you'll always get your (byte) count anyway - and dd always writes on a SIGINT as well. – mikeserv May 22 '15 at 3:52
  • @mikeserv I am not sure what you mean, about "Ctrl-C not being necessary". How do you indicate the end of the input, with STTY=-icanon cat | wc -c?? (The solution in the answer seems to be to kill cat, but this prevents wc from running, apparently.) – Eric O Lebigot May 22 '15 at 5:03
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    @EOL - Well, i figured wc was waiting on the end of a line. INT and TSTP will both flush i/o - but TSTP can be recovered. CTRL-Z + fg may help - but can you not just do CTRL-J? (it's the newline char). Alternatively you can: cat | ( trap '' INT; wc -c), but that assumes wc is well-behaved enough to die at the end of its input - probably a safe-assumption, though, given its purpose. dd, as mentioned, will always write on INT, and tee can be told to -ignore interrupts. Honestly, your heredoc idea was best, though - look at HIST_NO_STORE in man zshall. shly: set -o nolog. – mikeserv May 22 '15 at 5:22
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    @EOL - I wrote an answer here about how the stty eol setting might be used in some situations to overcome a canonical line-discipline's maximum line-length. It may be applicable to your problem as well. – mikeserv May 23 '15 at 0:35

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