How to disable line wrap in a terminal?

Question

I need to view large logs files using a bash shell. I was using less to open the files, but since the lines are too lengthy there is some kind of line/word wrapping going on.

Since the files are Log4J logs, and there is a pattern in the beginning of each line, having lines wrapped makes it difficult to analyze the output, so I started using less -S which chops long lines.

But now I need to use tail -f, and it also line wraps the output. Is it possible to disable line wrap in a bash shell for all the commands?

Note: there is an answer to a different question that mentions the escape sequence echo -ne '\e[?7l', but it seems to not work on bash.

Answer 1

Try:

less -S +F filename

=

less --chop-long-lines +F filename

And then:

• Press Ctrlc to stop tailing and now you can move left and right using cursor keys.
• Press Shiftf to resume tailing
• Press Ctrlc, q to quit

less manual: + If a command line option begins with +, the remainder of that option is taken to be an initial command to less.

For example, +F tells less to scroll forward, and keep trying to read when the end of file is reached

Answer 2

Found a good answer from superuser, that works out of the box for gnome-terminal, and probably for other terminals as well:

setterm -linewrap off

Answer 3

You can temporarily disable line wrapping by entering this command::

tput rmam

To restore line wrapping use this command:

tput smam

Answer 4

Supposing you have the COLUMNS variable defined, you can execute

tail -f your-app.log | cut -c -$COLUMNS

otherwise substitute $COLUMNS with the columns width of the terminal, as obtained by stty -a.

Answer 5

Do you actually need tail -f or would something like less +F do? Since it sounds like you still want an interactive pager, it seems to me it would be much easier to stick with less than to reimplement one yourself.

A final note: have you considered tail -f file | less?

Answer 6

Two good answers/examples here

http://www.commandlinefu.com/commands/view/1710/tail-a-log-file-with-long-lines-truncated

tail -f logfile.log | cut -b 1-80

tail -f logfile.log | cut -b -$(tput cols)

One caveat: at least on the built in terminal on my Mac cut does not seem to handle tab characters very well. It seems it displays them with e.g., 8 spaces but just calculates them as 4 space wide or something like that. In other words, if your terminal is 80 characters wide and your output contains several tabs per line you must set the width to maybe 60 or something like that. YMMV.

Answer 7

The terminator (http://software.jessies.org/terminator/) terminal emulator allow to not wrap long lines and has horizontal scrolling (but is written in Java).

Answer 8

There are a lot of comments which stray from the question. OP's question was

But now I need to use tail -f, and it also line wraps the output. Is it possible to disable line wrap in a bash shell for all the commands?

Some comments were made about the autowrap feature, stating that not all terminals have it. Perhaps. But (aside from terminator, whose developers document no terminal description) all of the examples given were xterm, rxvt and some look-alike or descendent. Those are all related.

The +aw option in xterm corresponds to the autoWrap resource. Consulting the manual, it says that

   autoWrap (class AutoWrap)
           Specifies  whether  or  not  auto-wraparound should be enabled.
           This is the same as the VT102 DECAWM.  The default is "true".

and in XTerm Control Sequences it says

CSI ? Pm h
          ...
          DEC Private Mode Set (DECSET).
            Ps = 7  -> Wraparound Mode (DECAWM).

which certainly does not "depend on your choice of terminal", since any terminal with VT100-compatibility supports the feature. xterm and rxvt do this, for example. The others do as well.

Whether the feature would be useful to OP is debatable. Suppressing line-wrapping is only one aspect of the problem:

• The shell knows the width of the terminal—but that can be overridden by setting COLUMNS to a "large" value.
• Of course that means that applications will spend a lot of time writing on the right-margin (and some, getting it wrong, will start a new line anyway).
• OP probably assumed that the application would scroll left/right to make the wide terminal usable. (terminator does this — partly — but its other drawbacks cancel that out, except for those who only use the terminal for cat'ing a logfile to the screen).
• what OP actually is looking for is a set of tools that can be told to disable line-wrap, especially for viewing logfiles. If the terminal works well enough for general use, it is irrelevant to the choice of tools which one uses within the terminal.

There are pagers which can do what is needed, e.g., multitail which lists in its features

Line wrapping can be switched off, after that one can scroll to the left/right with the cursor keys

Being ncurses-based, it should work on any of the cited terminals.

Answer 9

There are a few examples on this page piping tail with -f ... from my tests it doesn't work properly, if you really need piping (eg. if you need to pipe something more, like grep) you may use something like:

watch -n 1 'tail -n $(($LINES-3)) file.log | cut -c -$COLUMNS'

not the best for performance probably but works... else if no extra pipping required you may use something different like:

less -S +F file.log

Answer 10

Use below options with less. It will disable word wrap and preserve text colors, if specified.

less -SR +F filename

Answer 11

vi

inside vi type

:set nowrap

I beleive there is also a plugin for vi that will give you tail like behaviour.

Answer 12

If you really want to see the full lines you can copy and paste the text into a text editor like Atom or Notepad++ and disable line wraps in there.