Scripting – Use Less Without ESC Escape Characters

escape-characterslessscripting

When I use less at the command line the output is like

but when I use less from within a bash script I get:

How can I use less in a bash script and not get all the escape characters and have it work like it does at the interactive command line?

Best Answer

Use -R flag:

-r or --raw-control-chars

Causes "raw" control characters to be displayed. The default is to display control characters using the caret notation; for example, a control-A (octal 001) is displayed as "^A". Warning: when the -r option is used, less cannot keep track of the actual appearance of the screen (since this depends on how the screen responds to each type of control character). Thus, various display problems may result, such as long lines being split in the wrong place.

-R or --RAW-CONTROL-CHARS

Like -r, but only ANSI "color" escape sequences are output in "raw" form. Unlike -r, the screen appearance is maintained correctly in most cases. ANSI "color" escape sequences are sequences of the form:
           ESC [ ... m
where the "..." is zero or more color specification characters For the purpose of keeping track of screen appearance, ANSI color escape sequences are assumed to not move the cursor. You can make less think that characters other than "m" can end ANSI color escape sequences by setting the environment variable LESSANSIENDCHARS to the list of characters which can end a color escape sequence. And you can make less think that characters other than the standard ones may appear between the ESC and the m by setting the environment variable LESSANSIMIDCHARS to the list of characters which can appear.

From less man page.

Related Solutions

Shell – Escape sequences in output of script called from ncurses application

The reason why an event-script fails to send a "growler" message is that mcabber closes the standard input, output and error streams when it runs an event command. You can see this in hooks.c:

  if ((pid=fork()) == -1) {
    scr_LogPrint(LPRINT_LOGNORM, "Fork error, cannot launch external command.");
    g_free(datafname);
    return;   
  }    
  if (pid == 0) { // child
    // Close standard file descriptors
    close(STDIN_FILENO);
    close(STDOUT_FILENO);
    close(STDERR_FILENO);
    if (execl(extcmd, extcmd, arg_type, arg_info, bjid, arg_data,
              (char *)NULL) == -1) {
      // scr_LogPrint(LPRINT_LOGNORM, "Cannot execute external command.");
      exit(1);
    }
  }
  g_free(datafname);

That makes the event script run without interfering with the streams used by mcabber.

There is no special ncurses mode intercepting the message (after all, tmux is already running as a terminfo application). You can probably work around the problem by redirecting your echo (preferably printf) to /dev/tty, e.g.,

#!/bin/sh
printf '\033Ptmux;\033\033]9;foobar\007\033\\' >/dev/tty

Bash – Is it possible to use ANSI color escape codes in Bash here-documents

In your script, these assignments

normal='\e[0m'
yellow='\e[33m'

put those characters literally into the variables, i.e., \e[0m, rather than the escape sequence. You can construct an escape character using printf (or some versions of echo), e.g.,

normal=$(printf '\033[0m')
yellow=$(printf '\033[33m')

but you would do much better to use tput, as this will work for any correctly set up terminal:

normal=$(tput sgr0)
yellow=$(tput setaf 3)

Looking at your example, it seems that the version of printf you are using treats \e as the escape character (which may work on your system, but is not generally portable to other systems). To see this, try

yellow='\e[33m'
printf 'Yellow:%s\n' $yellow

and you would see the literal characters:

Yellow:\e[33m

rather than the escape sequence. Putting those in the printf format tells printf to interpret them (if it can).

Best Answer

Related Solutions

Shell – Escape sequences in output of script called from ncurses application

Bash – Is it possible to use ANSI color escape codes in Bash here-documents

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